Table of contents

A correction has been made to equation (3) of this paper. Please see the PDF file for details.

Corrections have been made to some equations in this paper. Please see the PDF file for details.

We investigate the emergence of target waves in a cyclic predator–prey model incorporating a periodic current of the three competing species in a small area situated at the center of a square lattice. The periodic current acts as a pacemaker, trying to impose its rhythm on the overall spatiotemporal evolution of the three species. We show that the pacemaker is able to nucleate target waves that eventually spread across the whole population, whereby three routes leading to this phenomenon can be distinguished depending on the mobility of the three species and the oscillation period of the localized current. First, target waves can emerge due to the synchronization between the periodic current and oscillations of the density of the three species on the spatial grid. The second route is similar to the first, the difference being that the synchronization sets in only intermittently. Finally, the third route toward target waves is realized when the frequency of the pacemaker is much higher than that characterizing the oscillations of the overall density of the three species. By considering the mobility and frequency of the current as variable parameters, we thus provide insights into the mechanisms of pattern formation resulting from the interplay between local and global dynamics in systems governed by cyclically competing species.

Based on single-photon spin–orbit entanglement, we propose in this paper an experimental scheme to sort orbital angular momentum (OAM) by cascading conventional polarizing beam splitters. An economical algorithm, taking advantage of the pair's complementary notation of OAM numbers, is designed to separate a mixture of definite OAM. Our scheme provides an alternative technique to encode OAM onto multiple spin states based on a Huffman tree and its potential in optical communication is demonstrated.

Ultracold dipolar Fermi gases represent relatively unexplored, strongly correlated systems arising from long-range and anisotropic interactions. We demonstrate the possibility of a spontaneous symmetry breaking biaxial phase in these systems, which may be realized in, e.g., gases of ultracold polar molecules or strongly magnetic atoms. This biaxial nematic phase is manifest in a spontaneous distortion of the Fermi surface perpendicular to the axis of polarization. We describe these dipolar interaction induced phases using Landau Fermi liquid theory.

We realize a deterministic single-photon source from one and the same calcium ion interacting with a high-finesse optical cavity. Photons are created in the cavity with efficiency 88±17%, a tenfold improvement over previous cavity-ion sources. Results of the second-order correlation function are presented, demonstrating a high suppression of two-photon events limited only by background counts. The cavity photon pulse shape is obtained, with good agreement between experiment and simulation. Moreover, theoretical analysis of the temporal evolution of the atomic populations provides relevant information about the dynamics of the process and opens the way to future investigations of a coherent atom–photon interface.

We use detrended fluctuation analysis (DFA) to study the dynamics of blood pressure oscillations and its feedback control in rats by analyzing systolic pressure time series before and after a surgical procedure that interrupts its control loop. We found, for each situation, a crossover between two scaling regions characterized by exponents that reflect the nature of the feedback control and its range of operation. In addition, we found evidence of adaptation in the dynamics of blood pressure regulation a few days after surgical disruption of its main feedback circuit. Based on the paradigm of antagonistic, bipartite (vagal and sympathetic) action of the central nerve system, we propose a simple model for pressure homeostasis as the balance between two nonlinear opposing forces, successfully reproducing the crossover observed in the DFA of actual pressure signals.

We measured a spatio-temporal distribution of particle size and a spatial growth rate in a capacitively coupled silane plasma using in situ multi-pass laser light scattering. The two-dimensional measurement was accomplished using a low power He–Ne laser and a set of spherical mirrors across the plasma that enables us to span multiple beam paths over the plasma region in the vertical direction from the electrode sheath to the bulk plasma. In temporal, the measurement result shows two particle growth periods in which the fast particle growth (nucleation) is followed by the slow particle growth (coagulation). In spatial, the fastest particle growth occurred at the highest vertical position that corresponds to the furthest position from the sheath. The particle coagulation modeling indicates that it is consistent with the largest proto particle creation rate in the plasma bulk.

The Karlsruhe Tritium Neutrino (KATRIN) experiment aims to determine the absolute mass of the electron antineutrino from a precise measurement of the tritium β-spectrum near its endpoint at 18.6 keV with a sensitivity of 0.2 eV c⁻². KATRIN uses an electrostatic retardation spectrometer of MAC-E filter type for which it is crucial to monitor high voltages of up to 35 kV with a precision and long-term stability at the ppm level. Since devices capable of this precision are not commercially available, a new high voltage divider for direct voltages of up to 35 kV has been designed, following the new concept of the standard divider for direct voltages of up to 100 kV developed at the Physikalisch-Technische Bundesanstalt (PTB)PTB is the German National Metrology Institute providing scientific and technical services.. The electrical and mechanical design of the divider, the screening procedure for the selection of the precision resistors, and the results of the investigation and calibration at the PTB are reported here. During the latter, uncertainties at the low ppm level have been deduced for the new divider, thus qualifying it for the precision measurements of the KATRIN experiment.

In the endeavour to scale up the number of qubits in an ion-based quantum computer several groups have started to develop miniaturized ion traps for extended spatial control and manipulation of the ions. Shuttling and separation of ion strings have been the foremost issues in linear-trap arrangements and some prototypes of junctions have been demonstrated for the extension of ion motion to two dimensions (2D). While junctions require complex trap structures, small extensions to the 1D motion can be accomplished in simple linear trap arrangements. Here, control of the extended field in a planar, linear chip trap is used to shuttle ions in 2D. With this approach, the order of ions in a string is deterministically reversed. Optimized potentials are theoretically derived and simulations show that the reordering can be carried out adiabatically. The control over individual ion positions in a linear trap presents a new tool for ion-trap quantum computing. The method is also expected to work with mixed crystals of different ion species and as such could have applications for sympathetic cooling of an ion string.

Surface exciton polaritons (SEPs) were mostly expected in materials displaying sharp excitonic absorptions. Using electron energy-loss spectroscopy with a spatial resolution of 0.2–2 nm and associated calculations, we demonstrated SEPs upon rather weak excitonic oscillator strengths (broad interband transitions) in insulating, monoclinic HfO₂ above its optical band gap. Broad interband transitions exist in many semiconductors and insulators above the band gap, and our work could stimulate future explorations of SEPs in a wide spectrum of materials and corresponding applications in optics.

The physical processes in an Ar/O₂ magnetron discharge used for the reactive sputter deposition of TiO_x thin films were simulated with a 2d3v particle-in-cell/Monte Carlo collisions (PIC/MCC) model. The plasma species taken into account are electrons, Ar⁺ ions, fast Ar_f atoms, metastable Ar_m^* atoms, Ti⁺ ions, Ti atoms, O⁺ ions, O₂⁺ ions, O⁻ ions and O atoms. This model accounts for plasma–target interactions, such as secondary electron emission and target sputtering, and the effects of target poisoning. Furthermore, the deposition process is described by an analytical surface model. The influence of the O₂/Ar gas ratio on the plasma potential and on the species densities and fluxes is investigated. Among others, it is shown that a higher O₂ pressure causes the region of positive plasma potential and the O⁻ density to be more spread, and the latter to decrease. On the other hand, the deposition rates of Ti and O are not much affected by the O₂/Ar proportion. Indeed, the predicted stoichiometry of the deposited TiO_x film approaches x=2 for nearly all the investigated O₂/Ar proportions.

We have investigated the evolution of occupied and unoccupied electronic states of tris-(8-hydroxyquinoline) aluminum (Alq₃) molecules adsorbed on Cu(100) using ultraviolet photoelectron spectroscopy and interferometric time-resolved two-photon photoemission (ITR-2PPE). The adsorption of Alq₃ lowers the work function of the surface, which allows an unambiguous observation of Cu(100) surface resonance coupled with d-band state and molecular interband transition in our ITR-2PPE setup. No evidence of an anion state, which used to be formed by dynamic charge transfer from metal to a molecular unoccupied state, is identified. Analysis of relaxation dynamics of the transiently occupied electronic states shows that the lifetimes for those excited states at this surface are independent of the Alq₃ thickness. These results indicate that the Alq₃–Cu(100) interface is described as a weak van der Waals interaction.

Kinetic Boltzmann equations are used to describe electron emission spectra obtained after irradiation of noble-gas clusters with intense vacuum ultraviolet (VUV) radiation from a free-electron-laser (FEL). The experimental photoelectron spectra give a complementary and more detailed view of nonlinear processes within atoms and clusters in an intense laser field compared to mass spectroscopy data. Results from our model obtained in this study confirm the experimental and theoretical findings on the differing ionization scenarios at longer (100 nm) and shorter (32 nm) VUV radiation wavelengths. At the wavelength of 100 nm the thermoelectronic electron emission dominates the emission spectra. This indicates the plasma formation and the inverse bremsstrahlung (IB) heating of electrons inside the plasma. This effect is clearly visible for xenon (with the fitted temperature of 6–7 eV), and less visible for argon (with the fitted temperature of 2–3 eV). The two-photon-ionization rate for argon that initiates the cluster ionization, is much lower than the single-photoionization rate for xenon. Also, more of the photoelectrons created within an argon cluster are able to leave it, as they are more energetic than those released from a xenon cluster. Therefore, the IB heating of plasma electrons in argon is less efficient than in xenon, as the density of the electrons remaining within the cluster is lower.

At a wavelength of 32 nm the dominant ionization mechanism identified from the electron spectra of argon clusters is the direct multistep ionization. The signature of the thermalization of electrons is also observed. However, as the heating of electrons due to the inverse bremsstrahlung process is weak at these radiation wavelengths and pulse fluences, the increase of the electron temperature with the pulse intensity is mainly due to the increasing photoionization rate within the irradiated sample.

We disclose the basic mechanism of agglomeration of nano-sized particles. While for weakly coupled, mono-dispersed particles the electrostatic agglomeration has always been found to be unlikely, in strongly coupled complex (dusty) plasmas the occupation of positive states for small particles is relevant, leading to electrostatic attraction between differently charged particles. The occupation of positively charged states is further enhanced by dispersed distribution of size. The smaller particles are trapped by the larger, the accretion of which gives a positive feedback on the probability of positively charged small grains and then further accretion. Experiments on growth of carbon particles from sputtered graphite in RF and dc Argon plasma confirm the general theoretical prediction when the energy of the ions corresponds to plasma boundaries.

Pressure-induced structural and electronic variations of Se helical chains confined in nano-channels of zeolite single crystals are studied. Raman and optical absorption spectra provide us with evidence of softened vibration modes and band gap reduction under high pressure. We reveal that the Se chains elongate under hydrostatic compression by ab initio calculations. The changes in morphology lead to a softening of phonons and narrowing of energy gaps consistent with observations from optical measurements. The present investigation demonstrates negative compressibility of Se chains in one-dimensional channels of a zeolite framework.

Hard and soft x-ray photoelectron spectroscopies (called HAXPES and SXPES) were performed at ∼8 and ∼1.25 keV for the metal–insulator transitions (MIT) system VO₂. From the sharp difference between HAXPES and SXPES in the O 1s spectra, it was found that the clean surface of the metal VO₂ is covered with a less itinerant surface layer. Clear changes of the spectral shapes were observed in HAXPES on MIT for the V 1s, 2p, 3s, 3p and O 1s core levels. The enhanced intensity of these core levels in the low-binding-energy (E_B) region of the main peak in the metal phase is due to the non-local or long range screening effects. The V 3d valence band in the metal phase is composed of coherent and incoherent parts. The prominent peak near 0.9 eV in the insulator phase has an incoherent tail in the high-E_B region and the peak and its lower E_B components are understood to have a noticeable coherent component. It is experimentally confirmed that both electron correlation and band changes induced by lattice distortion are responsible for the spectral changes on MIT in VO₂.

We experimentally generate and characterize a six-photon polarization entangled state, which is usually called 'Ψ₆⁺'. This is realized with a filtering procedure of triple emissions of entangled photon pairs from a single source, which does not use any interferometric overlaps. The setup is very stable and we observe the six-photon state with high fidelity. The observed state can be used for demonstrations of telecloning and secret sharing protocols.

We have studied the delivery of a colloidal particle in the presence of an oscillating, spatially periodic, optical potential. The average particle velocity relative to the fluid velocity in this potential depends greatly on the oscillation amplitude and frequency. The results of both our simulations and experiments show that for some combinations of these parameters, the average particle transportation velocity can be enhanced due to the synchronization of the particle's movement with the oscillating potential.

The purpose of this paper is twofold: (i) to advance and extend the statistical two-point models of pair dispersion and particle clustering in isotropic turbulence that were previously proposed by Zaichik and Alipchenkov (2003 Phys. Fluids15 1776–87; 2007 Phys. Fluids 19, 113308) and (ii) to present some applications of these models. The models developed are based on a kinetic equation for the two-point probability density function of the relative velocity distribution of two particles. These models predict the pair relative velocity statistics and the preferential accumulation of heavy particles in stationary and decaying homogeneous isotropic turbulent flows. Moreover, the models are applied to predict the effect of particle clustering on turbulent collisions, sedimentation and intensity of microwave radiation as well as to calculate the mean filtered subgrid stress of the particulate phase. Model predictions are compared with direct numerical simulations and experimental measurements.

Identifying the many-body Hamiltonian of a large quantum system is essential in understanding many physical phenomena, yet extremely difficult in general. We show that coupling strengths in networks of spin-1/2 particles can be estimated indirectly through a gateway, provided that the coupling topology is known. The criterion for the feasibility of identification is described only by a simple topological property concerning how the gateway is connected to the entire network. We also address the issues of process efficiency and how degeneracies of the system can be lifted.

Numerical simulations, based on a finite-difference-time-domain (FDTD) method, of infrared light propagation for add/drop filtering in two-dimensional (2D) metal–insulator–metal (Ag–SiO₂–Ag) resonators are reported to design 2D Y-bent plasmonic waveguides with possible applications in telecommunication wavelength demultiplexing (WDM). First, we study optical transmission and reflection of a nanoscale SiO₂ waveguide coupled to a nanocavity of the same insulator located either inside or on the side of a linear waveguide sandwiched between Ag. According to the inside or outside positioning of the nanocavity with respect to the waveguide, the transmission spectrum displays peaks or dips, respectively, which occur at the same central frequency. A fundamental study of the possible cavity modes in the near-infrared frequency band is also given. These filtering properties are then exploited to propose a nanoscale demultiplexer based on a Y-shaped plasmonic waveguide for separation of two different wavelengths, in selection or rejection, from an input broadband signal around 1550 nm. We detail coupling of the 2D add/drop Y connector to two cavities inserted on each of its branches. Selection or rejection of a pair of different wavelengths depends on the inside or outside locations (respectively) of each cavity in the Y plasmonic device.

We experimentally investigate electromagnetically induced transparency (EIT) created on an inhomogeneously broadened 5S_1/2–5P_1/2 transition in rubidium vapor using a control field of a complex temporal shape. A comb-shaped transparency spectrum enhances the delay-bandwidth product and the light storage capacity for a matched probe pulse by a factor of about 50 compared to a single EIT line (Yavuz 2007 Phys. Rev. A 75 031801). If the temporal mode of the control field is slowly changed while the probe is propagating through the EIT medium, the probe will adiabatically follow, providing a means to perform frequency conversion and optical routing.

Cylindrical and spherical dust-acoustic (DA) shock waves propagating in a strongly coupled dusty plasma are theoretically investigated. The generalized hydrodynamic model, in which highly charged dust are treated as strongly coupled, but electrons and ions are treated as weakly coupled, is employed. The modified Burgers equation, which is derived by using the reductive perturbation technique, is numerically solved to examine the effects of nonplanar cylindrical and spherical geometries on the basic features of the DA shock waves that are formed due to a strong correlation among highly negatively charged dust. It is shown that the effects of nonplanar cylindrical and spherical geometries significantly modify the basic properties of the DA shock structures. The implications of our results in laboratory dusty plasma experiments are briefly discussed.

Entangled states of quantum systems can give rise to measurement correlations of separated observers that cannot be described by local hidden variable theories. Usually, it is assumed that entanglement between particles is generated due to some distance-dependent interaction. Yet anyonic particles in two dimensions have a nontrivial interaction that is purely topological in nature. In other words, it does not depend on the distance between two particles, but rather on their exchange history. The information encoded in anyons is inherently non-local even in the single subsystem level making the treatment of anyons non-conventional. We describe a protocol to reveal the non-locality of anyons in terms of correlations in the outcomes of measurements in two separated regions. This gives a clear operational measure of non-locality for anyonic states and it opens up the possibility to test Bell inequalities in quantum Hall liquids or spin lattices.

We report a high fidelity tomographic reconstruction of the quantum state of photon pairs generated by parametric down-conversion with orbital angular momentum (OAM) entanglement. Our tomography method allows us to estimate an upper and lower bound for the entanglement between the down-converted photons. We investigate the two-dimensional state subspace defined by the OAM states ±ℓ and superpositions thereof, with ℓ=1, 2, ..., 30. We find that the reconstructed density matrix, even for OAMs up to around ℓ=20, is close to that of a maximally entangled Bell state with a fidelity in the range between F=0.979 and F=0.814. This demonstrates that, although the single count-rate diminishes with increasing ℓ, entanglement persists in a large dimensional state space.

Using Gutzwiller's semiclassical periodic-orbit theory, we demonstrate universal behavior of the two-point correlator of the density of levels for quantum systems whose classical limit is fully chaotic. We go beyond previous work in establishing the full correlator such that its Fourier transform, the spectral form factor, is determined for all times, below and above the Heisenberg time. We cover dynamics with and without time-reversal invariance (from the orthogonal and unitary symmetry classes). A key step in our reasoning is to sum the periodic-orbit expansion in terms of a matrix integral, like the one known from the sigma model of random matrix theory.

We study the concentration dependence of the superconducting critical temperature T_c in a boron-doped diamond. We evaluate the density of states at Fermi level N₀ within the dynamical cluster approximation obtaining higher values than from the coherent potential approximation. We discuss T_c as a function of N₀ within the BCS, the McMillan and the Belitz theory. The simplified Belitz theory gives the best agreement with experimental data. Since the density of states follows a simple power law for accessible doping concentrations x, the present theory offers an analytical formula for T_c(x).

Using atomistic simulations and an embedded-atom interatomic potential, which is capable of describing the martensite (fcc → bcc) transition in Fe, we compare the Bain and Nishiyama–Wassermann transformation paths. We calculate the minimum-energy paths for these two transformations at 0 K. For finite temperature, we study the evolution of the free energy along the two paths, calculated via the method of metric scaling, which shows only small differences. However, the variation of the elements of the stress tensor, and of the atomic volume, show clear differences: the Bain path leads to by a factor of five higher compressive pressures compared to the Nishiyama–Wassermann path. This means that the Bain path requires additional work applied on the system in order to accomplish it, and gives atomistic evidence that the martensite transformation rather follows the Nishiyama–Wassermann path in reality.

Using nonlinear system theory and numerical simulations, we map out the static and dynamic phase diagrams in the zero applied field of a spin torque nano device with a tilted polarizer (TP). We find that for sufficiently large currents, even very small tilt angles (β>1°) will lead to steady free layer precession in zero field. Within a rather large range of tilt angles, 1°<β<19°, we find coexisting static states and hysteretic switching between these using only current. In a more narrow window (1°<β<5°) one of the static states turns into a limit cycle (precession). The coexistence of current-driven static and dynamic states in the zero magnetic field is unique to the TP device and leads to large hysteresis in the upper and lower threshold currents for its operation. The nano device with TP can facilitate the generation of large amplitude mode of spin torque signals without the need for cumbersome magnetic field sources and thus should be very important for future telecommunication applications based on spin transfer torque effects.

We have presented a novel family of paraxial laser beams, which are called Airy complex variable function Gaussian (ACVF–Gaussian) beams. The ACVF–Gaussian beams are formed by the product of an Airy complex variable function and a Gaussian function. Unlike Airy–Gaussian beams, which are nondiffracting, the ACVF–Gaussian beams, which have a rotating phase term are diffracting and rotating. The rotating velocity decreases when the propagation distance increases. We have analyzed the evolution of the Poynting vector and angular momentum density of the ACVF–Gaussian beams as they propagate in free space.

In this work, we use inelastic scattering of light to study the response of inhomogeneous Mott-insulator gases to external excitations. The experimental setup and procedure to probe the atomic Mott states are presented in detail. We discuss the link between the energy absorbed by the gases and accessible experimental parameters as well as the linearity of the response to the scattering of light. We investigate the excitations of the system in multiple energy bands and a band-mapping technique allows us to identify band and momentum of the excited atoms. In addition, the momentum distribution in the Mott states that is spread over the entire first Brillouin zone enables us to reconstruct the dispersion relation in the high energy bands using a single Bragg excitation with a fixed momentum transfer.

Thermal properties of open-shell metallic nanoparticles of elements that are not magnetic in the bulk are studied within the framework of the local spin density approximation at finite temperature. For bulk ferromagnetic materials, these nanosized objects undergo a second-order critical phenomenon at a temperature that strongly depends on electron correlations and the size of the nanoparticle. The magnetic susceptibility is found to obey the Curie–Weiss law, which is in agreement with recent experimental measurements performed on mass-selected platinum clusters.

The experiments on strongly nonequilibrium symmetry-breaking phase transformations in superfluids and superconductors revealed that the topological defects (e.g. vortices) are produced most efficiently in the systems of microscopic size or low dimensionality (D=1), while in the macroscopic two-dimensional (2D) and 3D samples the efficiency of their formation was substantially suppressed (by a few orders of magnitude) as compared to theoretical predictions. A reasonable explanation for this behaviour is based on the specific thermal correlations between the phases of Bose–Einstein condensates formed in the spatial subregions disconnected during the phase transformation. Such correlations were initially revealed in the multi-Josephson-junction loop experiment (Carmi R et al 2000 Phys. Rev. Lett. 84 4966) and were confirmed recently by the experiments with ultracold atoms in periodic potentials (Hadzibabic Z et al 2006 Nature 441 1118). We begin our theoretical consideration from a phase transformation in the simplest φ⁴-model of the real scalar field and show that, under the presence of the above-mentioned correlations, the final symmetry-broken states are described by the effective Ising model. Its behaviour changes dramatically in passing from finite to infinite size of the system and from the low (D=1) to higher (D⩾2) dimensionality, which is in qualitative agreement with the experimental results.

It is argued that an ultracold quantum degenerate gas of ytterbium ¹⁷³Yb atoms having nuclear spin I=5/2 exhibits an enlarged SU(6) symmetry. Within the Landau Fermi liquid theory, stability criteria against Fermi liquid (Pomeranchuk) instabilities in the spin channel are considered. Focusing on the SU(n>2) generalizations of ferromagnetism, it is shown within mean-field theory that the transition from the paramagnet to the itinerant ferromagnet is generically first order. On symmetry grounds, general SU(n) itinerant ferromagnetic ground states and their topological excitations are also discussed. These SU(n>2) ferromagnets can become stable by increasing the scattering length using optical methods or in an optical lattice. However, in an optical lattice at current experimental temperatures, Mott states with different filling are expected to coexist in the same trap, as obtained from a calculation based on the SU(6) Hubbard model.

In a planar, laterally extended dielectric barrier discharge (DBD) system operated in glow mode, a filamentary discharge is observed. The filaments tend to move laterally and hence tend to cause collisions. Thereby, usually one collision partner becomes destroyed. In this paper, the collision process and especially the preceding time period is investigated. Beside the luminescence density of the filaments, the surface charge density accumulated between the single breakdowns of the DBD is observed via an optical measurement technique based on the linear electro-optical effect (pockels effect). A ring-like substructure of the surface charge distribution of a single filament is found, which correlates to the filament interaction behaviour. Furthermore, a preferred filament distance is found, suggesting the formation of a filamentary quasi-molecule.

We study quantum algorithms implemented within a single harmonic oscillator, or equivalently within a single mode of the electromagnetic field. Logical states correspond to functions of the canonical position, and the Fourier transform to canonical momentum serves as the analogue of the Hadamard transform for this implementation. This continuous variable version of quantum information processing has widespread appeal because of advanced quantum optics technology that can create, manipulate and read Gaussian states of light. We show that, contrary to a previous claim, this implementation of quantum information processing has limitations due to a position–momentum trade-off of the Fourier transform, analogous to the famous time-bandwidth theorem of signal processing.

Total and positronium formation cross sections have been measured for positron scattering from H₂O and HCOOH using a positron beam with an energy resolution of 60 meV (full-width at half-maximum (FWHM)). The energy range covered is 0.5–60 eV, including an investigation of the behavior of the onset of the positronium formation channel using measurements with a 50 meV energy step, the result of which shows no evidence of any channel coupling effects or scattering resonances for either molecule.

Device independent quantum key distribution (QKD) aims to provide a higher degree of security than traditional QKD schemes by reducing the number of assumptions that need to be made about the physical devices used. The previous proof of security by Pironio et al (2009 New J. Phys. 11 045021) applies only to collective attacks where the state is identical and independent and the measurement devices operate identically for each trial in the protocol. We extend this result to a more general class of attacks where the state is arbitrary and the measurement devices have no memory. We accomplish this by a reduction of arbitrary adversary strategies to qubit strategies and a proof of security for qubit strategies based on the previous proof by Pironio et al and techniques adapted from Renner.

We present an ab initio study of the electron–phonon interaction in the surface electronic states on Pd(111). The calculations based on density-functional theory were carried out using a linear response approach and a mixed-basis pseudopotential method. We find that the electron–phonon coupling on Pd(111) both in the surface electronic states and at the Fermi energy is largely determined by bulk electronic states and bulk phonon modes. It is shown that the strength of the electron–phonon interaction and its variation with electron energy and momentum depend first of all on the particular surface energy band. However, the directional anisotropy in the electron–phonon coupling is weak.

We present a novel imaging system for ultracold quantum gases in expansion. After release from a confining potential, atoms fall through a sheet of resonant excitation laser light and the emitted fluorescence photons are imaged onto an amplified CCD camera using a high numerical aperture optical system. The imaging system reaches an extraordinary dynamic range, not attainable with conventional absorption imaging. We demonstrate single-atom detection for dilute atomic clouds with high efficiency where at the same time dense Bose–Einstein condensates can be imaged without saturation or distortion. The spatial resolution can reach the sampling limit as given by the 8 μm pixel size in object space. Pulsed operation of the detector allows for slice images, a first step toward a three-dimensional (3D) tomography of the measured object. The scheme can easily be implemented for any atomic species and all optical components are situated outside the vacuum system. As a first application we perform thermometry on rubidium Bose–Einstein condensates created on an atom chip.

A scheme for creating NOON-states of the quasi-momentum of ultra-cold atoms has recently been proposed (2006 New J. Phys. 8 180). This was achieved by trapping the atoms in an optical lattice in a ring configuration and rotating the potential at a rate equal to half a quantum of angular momentum. In this paper, we present a scheme for confirming that a NOON-state has indeed been created. This is achieved by spectroscopically mapping out the anti-crossing between the ground and first excited levels by modulating the rate at which the potential is rotated. Finally, we show how the NOON-state can be used to make precision measurements of rotation.

We demonstrate that it is possible to lock the radius of an optically trapped salt-water microdroplet to the n=1 whispering gallery resonances (WGRs) at the trapping laser wavelength. The optical properties of the droplet are determined using stimulated Raman scattering. The droplet is in thermodynamic equilibrium with the surrounding vapour and the proposed locking mechanism consists of a balance between bulk heating and WGR heating. Raman measurements allow the size parameter (nka) of the droplet to be determined with a precision of ∼10⁻⁵ and the resonance linewidth to be estimated.

A scheme to obtain brilliant x-ray sources by coherent reflection of a counter-propagating pulse from laser-driven dense electron sheets is theoretically and numerically investigated in a self-consistent manner. A radiation pressure acceleration model for the dynamics of the electron sheets blown out from laser-irradiated ultrathin foils is developed and verified by PIC simulations. The first multidimensional and integral demonstration of the scheme by 2D PIC simulations is presented. It is found that the reflected pulse undergoes Doppler-upshift by a factor 4γ_z², where γ_z=(1- v_z²/c²)^-1/2 is the effective Lorentz factor of the electron sheet along its normal direction. Meanwhile the pulse electric field is intensified by a factor depending on the electron density of the sheet in its moving frame n_e/γ, where γ is the full Lorentz factor.

For random walks on networks (graphs), it is a theoretical challenge to explicitly determine the mean first-passage time (MFPT) between two nodes averaged over all pairs. In this paper, we study the MFPT of random walks using the famous T-graph, linking this important quantity to the resistance distance in electronic networks. We obtain an exact formula for the MFPT that is confirmed by extensive numerical calculations. This interesting quantity is derived through the recurrence relations resulting from the self-similar structure of the T-graph. The obtained closed-form expression shows that the MFPT increases approximately as a power-law function of the number of nodes, with the exponent lying between 1 and 2. Our research may further a deeper understanding of random walks on the T-graph.

A scheme is presented for entangling two separated nanomechanical oscillators by injecting broad band squeezed vacuum light and laser light into the ring cavity. We work in the resolved sideband regime. We find that in order to obtain the maximum entanglement of the two oscillators, the squeezing parameter of the input light should be about 1. We report significant entanglement over a very wide range of power levels of the pump and temperatures of the environment.

On the graphene moiré on Ir(111) a variety of highly perfect cluster superlattices can be grown as shown for Ir, Pt, W and Re. Even materials that do not form cluster superlattices upon room temperature deposition may be grown into such by low-temperature deposition or the application of cluster seeding through Ir as shown for Au, AuIr and FeIr. Criteria for the suitability of a material to form a superlattice are given and largely confirmed. It is proven that at least Pt and Ir form epitaxial cluster superlattices. The temperature stability of the cluster superlattices is investigated and understood on the basis of positional fluctuations of the clusters around their sites of minimum potential energy. The binding sites of Ir, Pt, W and Re cluster superlattices are determined and the ability to cover samples macroscopically with a variety of superlattices is demonstrated.

Transport and magnetic studies are performed on high-quality FeTe_0.60Se_0.40 single crystals to determine the upper critical field (H_c2), lower critical field (H_c1) and the critical current density (J_c). The value of the upper critical field H_c2 is very large, whereas the activation energy determined from the slope of the Arrhenius plots is found to be lower than that in the FeAs122 superconductors. The lower critical field is determined in the 'ab' and 'c' directions of the crystals, and found to have anisotropy Γ(=H_c1∥c/H_c1∥ab)∼4. The magnetic isotherms measured up to 12 T show the presence of fishtail behavior. The critical current density at 1.8 K of the single crystals is found to be almost the same in both the 'ab' and 'c' directions in the low-field regime.

We study the time evolution of N_q two-level atoms (or qubits) interacting with a single mode of a quantized radiation field. In the case of two qubits, we show that for a set of initial conditions the reduced density matrix of the atomic system approaches that of a pure state at , halfway between that start of the collapse and the first mini-revival peak, where t_r is the time of the main revival. The pure state approached is the same for a set of initial conditions and is thus termed an 'attractor state'. The set itself is termed the 'basin of attraction' and we concentrate on its features. Extending to more qubits, we find that attractors are a generic feature of the multiqubit Jaynes–Cummings model (JCM) and we therefore generalize the discovery by Gea–Banacloche for the one-qubit case. We give the 'basin of attraction' for N_q qubits and discuss the implications of the 'attractor' state in terms of the dynamics of N_q-body entanglement. We observe both the collapse and revival and the sudden birth/death of entanglement depending on the initial conditions.

It is well known that there is a total cancellation of factorizable infrared (IR) divergences in unitary interacting field theories, such as quantum electrodynamics (QED) and quantum gravity. In this paper, we show that such a cancellation does not happen in QED with background electric fields that can produce pairs. There is no factorization of IR divergences.

The epitaxial growth of Fe on flat and vicinal Au(111) was investigated with scanning tunneling microscopy (STM) and low-energy electron diffraction (LEED) in a comparative study. Below a critical film thickness we found a pseudomorphic growth behavior of Fe on flat and vicinal Au(111). Above the critical Fe overlayer thickness a phase transition from fcc(111) to bcc(110) occurs on both surfaces. As a result of this phase transition rectangular-shaped crystallites are formed on the surface. The predominant orientation of the crystallites is along all directions for Fe on flat Au(111). For Fe on vicinal Au(111), we observed that no crystallites are orientated along the step edges. For Fe on flat Au(111), we found that the phase transition starts at a higher Fe overlayer thickness but a lower Fe coverage is required before the transition is completed in comparison with Fe on vicinal Au(111). Our results obtained with STM and LEED allow us to directly link the growth directions of the bcc(110) crystallites with twofold symmetry to the crystallographic directions of the substrate surface with hexagonal symmetry.

Single crystals of CeFeAsO, large enough to study the anisotropy of the magnetic properties, were grown by an optimized Sn-flux technique. The high quality of our single crystals is apparent from the highest residual resistivity ratio (RRR)≈12, reported among undoped RFeAsO compounds (R=rare earth) as well as sharp anomalies in resistivity, specific heat, C(T), and thermal expansion at the different phase transitions. The magnetic susceptibility χ(T) presents a large easy-plane anisotropy consistent with the lowest crystal electric field doublet having a dominant Γ₆ character. Curie–Weiss-like susceptibilities for magnetic field parallel and perpendicular to the crystallographic c-axis do not reveal an influence of a staggered field on the Ce site induced by magnetic ordering of the Fe. Furthermore, the standard signatures for antiferromagnetic order of Ce at T_N^4f=3.7 K observed in χ(T) and C(T) are incompatible with a Zeeman splitting Δ≈10 K of the CEF ground state doublet at low temperature due to the Fe-magnetic order as previously proposed. Our results can be reconciled with the earlier observation by assuming a comparatively stronger effect of the Ce–Ce exchange leading to a reduction of this Zeeman splitting below 15 K.

We use drift and diffusion coefficients to reveal interactions between different oscillatory processes underlying a complex signal and apply the method to EEG δ and θ frequencies in the brain. By analysis of data recorded from rats during anæsthesia, we consider the stability and basins of attraction of fixed points in the phase portrait of the deterministic part of the retrieved stochastic process. We show that different classes of dynamics are associated with deep and light anæsthesia, and we demonstrate that the predominant directionality of the interaction is such that θ drives δ.

Two-photon anti-bunching at a beamsplitter is only possible if the photons are entangled in a specific state, anti-symmetric in the spatial modes. Thus, observation of anti-bunching is an indication of entanglement in a degree of freedom, which might not be easily accessible in an experiment. We experimentally demonstrate this concept in the case of the interference of two frequency-entangled photons with continuous frequency detunings. The principle of anti-symmetrization of the spatial part of a wavefunction and subsequent detection of hidden entanglement via anti-bunching at a beamsplitter may facilitate the observation of entanglement in other systems, like atomic ensembles or Bose–Einstein condensates. The analogue for fermionic systems would be to observe bunching.

Biological neuronal networks constitute a special class of dynamical systems, as they are formed by individual geometrical components, namely the neurons. In the existing literature, relatively little attention has been given to the influence of neuron shape on the overall connectivity and dynamics of the emerging networks. The current work addresses this issue by considering simplified neuronal shapes consisting of circular regions (soma/axons) with spokes (dendrites). Networks are grown by placing these patterns randomly in the two-dimensional (2D) plane and establishing connections whenever a piece of dendrite falls inside an axon. Several topological and dynamical properties of the resulting graph are measured, including the degree distribution, clustering coefficients, symmetry of connections, size of the largest connected component, as well as three hierarchical measurements of the local topology. By varying the number of processes of the individual basic patterns, we can quantify relationships between the individual neuronal shape and the topological and dynamical features of the networks. Integrate-and-fire dynamics on these networks is also investigated with respect to transient activation from a source node, indicating that long-range connections play an important role in the propagation of avalanches.

The study of molecular dynamics at the single-molecule level with fluorescence correlation spectroscopy (FCS) and far-field optics has contributed greatly to the functional understanding of complex systems. Unfortunately, such studies are restricted to length scales of >200 nm because diffraction does not allow further reduction of the measurement volume. This sets an upper limit on the applicable concentration of fluorescently labeled molecules and even more importantly, averages out details of nanoscale dynamics. By combining FCS and fluorescence intensity distribution analysis (FIDA) with sub-diffraction–resolution stimulated emission depletion (STED) nanoscopy, we remove this restriction and obtain open measurement volumes of nanoscale dimensions which are tunable in size. As a consequence, single-molecule studies can now be extended to nanoscale dynamics and may be applied to much larger, often endogenous concentrations. In solution, low-brightness signal from axial out-of-focus volume shells was taken into account by using both FCS and FIDA in conjunction to analyze the data. In two-dimensional systems, such as lipid membranes, the background is greatly reduced and measurements feature excellent signal-to-noise ratios. Measurement foci of down to 30 nm in diameter directly reveal anomalous diffusion of lipids in the plasma membrane of living cells and allow for the determination of on/off rates of the binding of lipids to other membrane constituents. Such important insight into the prominent biological question of lipid membrane organization or 'lipid rafts' shows that combining fluctuation analysis with STED-engineered ultra-small measurement volumes is a viable and powerful new approach to probing molecular dynamics on the nanoscale.

We examine the time evolution of cold atoms (impurities) interacting with an environment consisting of a degenerate bosonic quantum gas. The impurity atoms differ from the environment atoms, being of a different species. This allows one to superimpose two independent trapping potentials, each being effective only on one atomic kind, while transparent to the other. When the environment is homogeneous and the impurities are confined in a potential consisting of a set of double wells, the system can be described in terms of an effective spin-boson model, where the occupation of the left or right well of each site represents the two (pseudo)-spin states. The irreversible dynamics of such system is here studied exactly, i.e. not in terms of a Markovian master equation. The dynamics of one and two impurities is remarkably different in respect of the standard decoherence of the spin-boson system. In particular, we show: (i) the appearance of coherence oscillations, (ii) the presence of super and subdecoherent states that differ from the standard ones of the spin-boson model, and (iii) the persistence of coherence in the system at long times. We show that this behaviour is due to the fact that the pseudospins have an internal spatial structure. We argue that collective decoherence also prompts information about the correlation length of the environment. In a one-dimensional (1D) configuration, one can change even more strongly the qualitative behaviour of the dephasing just by tuning the interaction of the bath.

Modern optical networking techniques have the potential to greatly extend the applicability of quantum communications by moving beyond simple point-to-point optical links and by leveraging existing fibre infrastructures. We experimentally demonstrate many of the fundamental capabilities that are required. These include optical-layer multiplexing, switching and routing of quantum signals; quantum key distribution (QKD) in a dynamically reconfigured optical network; and coexistence of quantum signals with strong conventional telecom traffic on the same fibre. We successfully operate QKD at 1310 nm over a fibre shared with four optically amplified data channels near 1550 nm. We identify the dominant impairment as spontaneous anti-Stokes Raman scattering of the strong signals, quantify its impact, and measure and model its propagation through fibre. We describe a quantum networking architecture which can provide the flexibility and scalability likely to be critical for supporting widespread deployment of quantum applications.

The quest for the nature of dark matter has reached a historical point in time, with several different and complementary experiments on the verge of conclusively exploring large portions of the parameter space of the most theoretically compelling particle dark matter models. This focus issue on dark matter and particle physics brings together a broad selection of invited articles from the leading experimental and theoretical groups in the field. The leitmotif of the collection is the need for a multi-faceted search strategy that includes complementary experimental and theoretical techniques with the common goal of a sound understanding of the fundamental particle physical nature of dark matter. These include theoretical modelling, high-energy colliders and direct and indirect searches. We are confident that the works collected here present the state of the art of this rapidly changing field and will be of interest to both experts in the topic of dark matter as well as to those new to this exciting field.

Focus on Dark Matter and Particle Physics Contents

DARK MATTER AND ASTROPHYSICS

Scintillator-based detectors for dark matter searches I S K Kim, H J Kim and Y D Kim

Cosmology: small-scale issues Joel R Primack

Big Bang nucleosynthesis and particle dark matter Karsten Jedamzik and Maxim Pospelov

Particle models and the small-scale structure of dark matter Torsten Bringmann

DARK MATTER AND COLLIDERS

Dark matter in the MSSM R C Cotta, J S Gainer, J L Hewett and T G Rizzo

The role of an e+e- linear collider in the study of cosmic dark matter M Battaglia

Collider, direct and indirect detection of supersymmetric dark matter Howard Baer, Eun-Kyung Park and Xerxes Tata

INDIRECT PARTICLE DARK MATTER SEARCHES:EXPERIMENTS

PAMELA and indirect dark matter searches M Boezio et al

An indirect search for dark matter using antideuterons: the GAPS experiment C J Hailey

Perspectives for indirect dark matter search with AMS-2 using cosmic-ray electrons and positrons B Beischer, P von Doetinchem, H Gast, T Kirn and S Schael

Axion searches with helioscopes and astrophysical signatures for axion(-like) particles K Zioutas, M Tsagri, Y Semertzidis, T Papaevangelou, T Dafni and V Anastassopoulos

The indirect search for dark matter with IceCube Francis Halzen and Dan Hooper

DIRECT DARK MATTER SEARCHES:EXPERIMENTS

Gaseous dark matter detectors G Sciolla and C J Martoff

Search for dark matter with CRESST Rafael F Lang and Wolfgang Seidel

DIRECT AND INDIRECT PARTICLE DARK MATTER SEARCHES:THEORY

Dark matter annihilation around intermediate mass black holes: an update Gianfranco Bertone, Mattia Fornasa, Marco Taoso and Andrew R Zentner

Update on the direct detection of dark matter in MSSM models with non-universal Higgs masses John Ellis, Keith A Olive and Pearl Sandick

Dark stars: a new study of the first stars in the Universe Katherine Freese, Peter Bodenheimer, Paolo Gondolo and Douglas Spolyar

Determining the mass of dark matter particles with direct detection experiments Chung-Lin Shan

The detection of subsolar mass dark matter halos Savvas M Koushiappas

Neutrino coherent scattering rates at direct dark matter detectors Louis E Strigari

Gamma rays from dark matter annihilation in the central region of the Galaxy Pasquale Dario Serpico and Dan Hooper

DARK MATTER MODELS

The dark matter interpretation of the 511 keV line Céline Boehm

Axions as dark matter particles Leanne D Duffy and Karl van Bibber

Sterile neutrinos Alexander Kusenko

Dark matter candidates Lars Bergström

Minimal dark matter: model and results Marco Cirelli and Alessandro Strumia

Shedding light on the dark sector with direct WIMP production Partha Konar, Kyoungchul Kong, Konstantin T Matchev and Maxim Perelstein

Axinos as dark matter particles Laura Covi and Jihn E Kim

The identification of dark matter in our particle physics model is still an open question. Here, we argue that axinos can be successful dark matter candidates in models with supersymmetry and the axion solution of the strong CP problem. Axinos can be the lightest supersymmetric particle (LSP) or can be heavier than the LSP. Axinos can be produced at the right abundance by thermal scattering and, if they are the LSP, also by out of equilibrium decays of the lightest superpartner of SM fields (LSPSMs). On the other hand, heavier (not LSP) axinos can generate a part of the neutralino LSP dark matter. Depending on the nature of the supersymmetric spectrum, and if R-parity is strictly conserved or slightly broken, very different signals of the LSP axino scenario can arise in colliders and in astrophysics.

A weakly interacting massive particle (WIMP) provides an attractive dark matter candidate, and should be within reach of the next generation of high-energy colliders. We consider the process of direct WIMP pair-production, accompanied by an initial-state radiation photon, in electron–positron collisions at the proposed International Linear Collider (ILC). We present a parametrization of the differential cross section for this process which conveniently separates the model-independent information provided by cosmology from the model-dependent inputs from particle physics. As an application, we consider two simple models, one supersymmetric and another of the 'universal extra dimensions' (UED) type. The discovery reach of the ILC and the expected precision of parameter measurements are studied in each model. In addition, for each of the two examples, we also investigate the ability of the ILC to distinguish between the two models through a shape-discrimination analysis of the photon energy spectrum. We show that with sufficient beam polarization the alternative model interpretation can be ruled out in a large part of the relevant parameter space.

We recap the main features of minimal dark matter (MDM) and assess its status in the light of recent experimental data. The theory selects an electroweak 5-plet with hypercharge Y=0 as a fully successful DM candidate, automatically stable against decay and with no free parameters: DM is a fermion with a 9.6 TeV mass. The direct detection cross-section, predicted to be 10⁻⁴⁴ cm², is within reach of next-generation experiments. DM is accompanied by a charged fermion 166 MeV heavier: we discuss how it might manifest. Thanks to an electroweak Sommerfeld enhancement of more than 2 orders of magnitude, DM annihilations into W⁺W⁻ give, in the presence of a modest astrophysical boost factor, an e⁺ flux compatible with the PAMELA excess (but not with the ATIC hint for a peak: MDM instead predicts a quasi-power-law spectrum), a flux concentrated at energies above 100 GeV, and photon fluxes comparable with present limits, depending on the DM density profile.

An overview is given of various dark matter candidates. Among the many suggestions given in the literature, axions, inert Higgs doublet, sterile neutrinos, supersymmetric particles and Kaluza–Klein particles are discussed. The situation has recently become very interesting with new results on antimatter in the cosmic rays having dark matter as one of the leading possible explanations. Problems arising from this explanation and possible solutions are discussed, and the importance of new measurements is emphasized. If the explanation is indeed dark matter, a whole new field of physics, with unusual although not impossible mass and interaction properties, may soon open itself to discovery.

Neutrino masses imply a likely existence of gauge-singlet fermions, which may be very heavy but may also be light. In the latter case, sterile neutrinos appear in the low-energy theory. They can make up all or part of dark matter and can explain the observed velocities of pulsars because they are emitted anisotropically from a cooling neutron star born in a supernova explosion. The most promising detection opportunity is by using x-ray telescopes and searching for monochromatic x-ray photons emitted from decays of these particles in dark-matter-dominated halos.

We overview the current status of axions as dark matter. The axion is the pseudo-Nambu–Goldstone boson which arises from the Peccei–Quinn solution to the strong CP problem. Additionally, cold axion populations that can contribute to the dark matter of the universe will be generated via this mechanism. After reviewing these topics, we focus on constraints from the laboratory, astrophysics and cosmology. We discuss the current status of experimental searches and the consequences of the distribution of dark matter axions in the galactic halo for these searches. The axion remains an excellent candidate for the dark matter and future experiments, particularly the Axion Dark Matter eXperiment (ADMX), will cover a large fraction of the axion parameter space.

The 511 keV high-precision map obtained by the INTEGRAL/SPI experiment suggested a surprisingly large amount of positrons in our galaxy with respect to 'naive' astrophysical expectations. Although an astrophysical origin is not excluded, this signal may shed light on dark matter. Here we discuss a possible MeV dark matter interpretation of the 511 keV line and point out a possible way of validating the MeV dark matter scenario. In particular, we show that the number of electrons generated by MeV annihilating particles would be large enough to lead to a visible Sunyaev–Zel'dovich (SZ) effect signature in clusters of galaxies if their dark matter halo profile behaves as ρ(r)∝1/r^γ with γ>1 in the inner part (i.e. on distances corresponding to a sub-arcsecond resolution for an experiment dedicated to SZ measurement).

In this paper, we review the prospects for the Fermi satellite (formerly known as GLAST) to detect gamma rays from dark matter annihilations in the Central Region of the Milky Way, in particular, in the light of the recent observations and discoveries of Imaging Atmospheric Cherenkov Telescopes. While the existence of significant astrophysical backgrounds in this part of the sky limits Fermi's discovery potential to some degree, this can be mitigated by exploiting the peculiar energy spectrum and angular distribution of the dark matter annihilation signal relative to those of astrophysical backgrounds.

Neutrino-induced recoil events may constitute a background to direct dark matter searches, particularly for those detectors that strive to reach the ton-scale and beyond. This paper discusses the expected neutrino-induced background spectrum due to several of the most important sources, including solar, atmospheric, and diffuse supernova neutrinos. The largest rate arises from ⁸B produced solar neutrinos, providing upwards of ∼10³ events per ton-year over all recoil energies for the heaviest nuclear targets. However the majority of these ⁸B events are expected to be below the recoil threshold of modern detectors. The remaining neutrino sources are found to constitute a background to the weakly interacting massive particles (WIMP)-induced recoil rate only if the WIMP-nucleon cross section is less than 10⁻¹² pb. Finally the sensitivity to the diffuse supernova neutrino flux for non-electron neutrino flavors is discussed, and projected flux limits are compared with existing flux limits.

Dark matter halos of subsolar mass are the first bound objects to form in cold dark matter theories. In this paper, I discuss the present understanding of 'microhalos', their role in structure formation and the implications of their potential presence, in the interpretation of dark matter experiments.

In this paper, I review two data analysis methods for determining the mass (and eventually the spin-independent cross section on nucleons) of weakly interacting massive particles with positive signals from direct dark matter detection experiments: a maximum likelihood analysis with only one experiment and a model-independent method requiring at least two experiments. Uncertainties and caveats of these methods will also be discussed.

We have proposed that the first phase of stellar evolution in the history of the Universe may be dark stars (DSs), powered by dark matter (DM) heating rather than by nuclear fusion. Weakly interacting massive particles, which may be their own antipartners, collect inside the first stars and annihilate to produce a heat source that can power the stars. A new stellar phase results, a DS, powered by DM annihilation as long as there is DM fuel, with lifetimes from millions to billions of years. We find that the first stars are very bright (∼10⁶L_⊙) and cool (T_surf<10 000 K) during the DS phase, and grow to be very massive (500–1000 times as massive as the Sun). These results differ markedly from the standard picture in the absence of DM heating, in which the maximum mass is smaller and the temperatures are much hotter (T_surf> 50 000 K); hence DS should be observationally distinct from standard Pop III stars. Once the DM fuel is exhausted, the DS becomes a heavy main sequence star; these stars eventually collapse to form massive black holes that may provide seeds for supermassive black holes observed at early times as well as explanations for recent ARCADE data and for intermediate black holes.

We discuss the possibilities for the direct detection of neutralino dark matter via elastic scattering in variants of the minimal supersymmetric extension of the Standard Model (MSSM) with non-universal supersymmetry-breaking contributions to the Higgs masses, which may be either equal (NUHM1) or independent (NUHM2). We compare the ranges found in the NUHM1 and NUHM2 with that found in the MSSM with universal supersymmetry-breaking contributions to all scalar masses, the CMSSM. We find that both the NUHM1 and NUHM2 offer the possibility of larger spin-independent dark matter scattering cross sections than in the CMSSM for larger neutralino masses, since they allow the density of heavier neutralinos with large Higgsino components to fall within the allowed range by astrophysics. The NUHM1 and NUHM2 also offer more possibilities than the CMSSM for small cross sections for lower neutralino masses, since they may be suppressed by scalar and pseudoscalar Higgs masses that are larger than in the CMSSM.

The formation and evolution of black holes (BHs) inevitably affects the distribution of dark and baryonic matter in the neighborhood of the BH. These effects may be particularly relevant around Supermassive and Intermediate Mass Black Holes (IMBHs), the formation of which can lead to large dark matter (DM) overdensities, called spikes and mini-spikes, respectively. Despite being larger and more dense, spikes evolve at the very centers of galactic halos, in regions where numerous dynamical effects tend to destroy them. Mini-spikes may be more likely to survive, and they have been proposed as worthwhile targets for indirect DM searches. We review here the formation scenarios and the prospects for detection of mini-spikes, and we present new estimates for the abundances of mini-spikes to illustrate the sensitivity of such predictions to cosmological parameters and uncertainties regarding the astrophysics of BH formation at high redshift. We also connect the IMBHs scenario to the recent measurements of cosmic-ray electron and positron spectra by the PAMELA, ATIC, H.E.S.S. and Fermi collaborations.

The search for direct interactions of dark matter particles remains one of the most pressing challenges of contemporary experimental physics. A variety of different approaches is required to probe the available parameter space and to meet the technological challenges. Here, we review the experimental efforts towards the detection of direct dark matter interactions using scintillating crystals at cryogenic temperatures. We outline the ideas behind these detectors and describe the principles of their operation. Recent developments are summarized and various results from the search for rare processes are presented. In the search for direct dark matter interactions, the CRESST-II experiment delivers competitive limits, with a sensitivity below 5×10^-7 pb on the coherent WIMP-nucleon cross section.

Dark matter (DM) detectors with directional sensitivity have the potential of yielding an unambiguous positive observation of WIMPs as well as discriminating between galactic DM halo models. In this paper, we introduce the motivation for directional detectors, discuss the experimental techniques that make directional detection possible, and review the status of the experimental effort in this field.

We revisit the prospects for IceCube and similar kilometer-scale telescopes to detect neutrinos produced by the annihilation of weakly interacting massive dark matter particles (WIMPs) in the Sun. We emphasize that the astrophysics of the problem is understood; models can be observed or, alternatively, ruled out. In searching for a WIMP with spin-independent interactions with ordinary matter, IceCube is only competitive with direct detection experiments if the WIMP mass is sufficiently large. For spin-dependent interactions IceCube already has improved the best limits on spin-dependent WIMP cross sections by two orders of magnitude. This is largely due to the fact that models with significant spin-dependent couplings to protons are the least constrained and, at the same time, the most promising because of the efficient capture of WIMPs in the Sun. We identify models where dark matter particles are beyond the reach of any planned direct detection experiments while being within reach of neutrino telescopes. In summary, we find that, even when contemplating recent direct detection results, neutrino telescopes have the opportunity to play an important as well as complementary role in the search for particle dark matter.

Axions should be produced copiously in stars such as the Sun. The first part of this paper reviews the capabilities and performance of axion helioscopes. The mechanism they rely on is described and the experimental results for the interaction of solar axions and axion-like particles with matter are given. The second part is actually observationally driven. New results obtained with Monte Carlo simulation reconstruct solar observations, previously dismissed, supporting an axion(-like) involvement with m_a≈1–2×10⁻² eV c⁻². To further quantify the suggested solar observations as being originated by axions, additional theoretical work is needed. However, the recently suggested axion interaction with magnetic field gradients is a generic theoretical example that seems to reconcile for the first time current limits, derived from axion helioscopes, and potential axion-related solar x-ray activity, thus avoiding contradictions with the best experimental limits. Magnetic quadrupoles can be used to experimentally test this idea, thus becoming a new catalyst in axion experiments. Finally, a short outlook for the future is given, in view of the experimental expansion of axion research with the state-of-the-art orbiting x-ray observatories.

The AMS-2 experiment will be launched with the Space Shuttle Discovery and installed on the International Space Station in 2010. It is designed to perform precision spectroscopy of many different cosmic-ray species including electrons and positrons. While the nature of dark matter is as yet unknown, dark matter annihilating in the Galactic halo is a well-motivated source of cosmic-ray electrons and positrons. The cosmic-ray positron fraction data available so far show significant deviations between different measurements and from the expectation for purely secondary production. The differences between the measurements up to particle energies of 6 GeV can be understood in a framework of charge-sign-dependent solar modulation and the spectra show excellent agreement if corrected for these time-dependent effects. Recent observations of an excess in the high-energy electron spectrum by ATIC might be connected to the excess in the positron fraction. A possible source of both signatures could be dark matter annihilation or a nearby pulsar. A measurement of the anisotropy of high-energy electrons could distinguish between both scenarios. Therefore the sky coverage of AMS-2 will be discussed in addition to possible dark matter scenarios and the sensitivity of the AMS-2 experiment to these effects.

The general antiparticle spectrometer (GAPS) experiment is an indirect dark matter search. GAPS detects the antideuterons produced in WIMP–WIMP annihilation, a generic feature in many theories beyond the Standard Model. Antideuterons are a nearly background free signature of exotic physics. GAPS has substantial discovery potential for dark matter within the minimal supersymmetric model and its extensions, and models with universal extra dimensions. GAPS complements underground experiments, reaching parts of supersymmetric parameter space unavailable to them, and working to better constrain the properties of dark matter where they overlap in parameter space. GAPS is designed to be launched from a balloon. GAPS is funded for a prototype flight in 2011, to be followed by a long duration balloon flight to execute its science program. We discuss recent theoretical investigations on antideuteron searches, and their implications for experiment design. We describe the GAPS experiment placing particular emphasis on recent investigations that represent technical or conceptual extensions of the original GAPS concept.

We present a review of the experimental results obtained by PAMELA in measuring the and e^± abundance in cosmic rays. In this context, we discuss the interpretation of the observed anomalous positron excess in terms of the annihilation of dark matter particles as well as in terms of standard astrophysical sources. Moreover we show the constraints on dark matter models from data.

We present an overview of supersymmetry (SUSY) searches, both at collider experiments and via searches for dark matter (DM). We focus on three DM possibilities in the SUSY context: the thermally produced neutralino, a mixture of axion and axino, and the gravitino, and compare and contrast signals that may be expected at colliders, in direct detection (DD) experiments searching of DM relics left over from the Big Bang, and indirect detection (ID) experiments designed to detect the products of DM annihilations within the solar interior or galactic halo. Detection of DM particles using multiple strategies provides complementary information that may shed light on the new physics associated with the DM sector. In contrast to the minimal supergravity (mSUGRA) model where the measured cold DM relic density restricts us to special regions mostly on the edge of the m₀–m_1/2 plane, the entire parameter plane becomes allowed if the universality assumption is relaxed in models with just one additional parameter. Then, thermally produced neutralinos with a well-tempered mix of wino, bino and higgsino components, or with a mass adjusted so that their annihilation in the early Universe is Higgs-resonance-enhanced, can be the DM. Well-tempered neutralinos typically yield heightened rates for DD and ID experiments compared with generic predictions from mSUGRA. If instead DM consists of axinos (possibly together with axions) or gravitinos, then there exists the possibility of detection of quasi-stable next-to-lightest SUSY particles at colliding beam experiments, with especially striking consequences if the next-lightest-supersymmetric-particle (NLSP) is charged, but no DD or ID detection. The exception for mixed axion/axino DM is that DD of axions may be possible.

The potential of a high energy, high luminosity e⁺e⁻ linear collider in the study of a weakly interacting massive new particle as a cosmic dark matter candidate is reviewed, with special emphasis on supersymmetric scenarios. Results of detailed simulation studies for supersymmetric neutralino dark matter indicate that the accuracy from linear collider data of sufficient energy may allow us to infer the dark matter relic density to accuracies comparable to those already obtained from the study of cosmic microwave background and other astrophysical data, thus providing a powerful test on the nature of dark matter by combining results from particle colliders with satellite and direct detection experiment data.

We have recently examined a large number of points in the parameter space of the phenomenological minimal supersymmetric Standard Model (MSSM), the 19-dimensional parameter space of the CP-conserving MSSM with minimal flavor violation. We determined whether each of these points satisfied existing experimental and theoretical constraints. This analysis provides insight into general features of the MSSM without reference to a particular SUSY breaking scenario or any other assumptions at the Grand Unified Theory (GUT) scale. This study opens up new possibilities for supersymmetry (SUSY) phenomenology at colliders as well as in both direct and indirect detection searches for dark matter.

The kinetic decoupling of weakly interacting massive particles (WIMPs) in the early universe sets a scale that can directly be translated into a small-scale cutoff in the spectrum of matter density fluctuations. The formalism presented here allows a precise description of the decoupling process and thus the determination of this scale to a high accuracy from the details of the underlying WIMP microphysics. With decoupling temperatures of several MeV to a few GeV, the smallest protohalos to be formed range between 10^-11 and almost 10^-3 solar masses—a somewhat smaller range than what was found earlier using order-of-magnitude estimates for the decoupling temperature; for a given WIMP model, the actual cutoff mass is typically about a factor of 10 greater than derived in that way, though in some cases the difference may be as large as a factor of several hundreds. Observational consequences and prospects to probe this small-scale cutoff, which would provide a fascinating new window into the particle nature of dark matter, are discussed.

We review how our current understanding of light element synthesis during the Big Bang nucleosynthesis era may help to shed light on the identity of particle dark matter.

The abundance of dark matter satellites and subhalos, the existence of density cusps at the centers of dark matter halos and problems producing realistic disk galaxies in simulations are issues that have raised concerns about the viability of the standard cold dark matter (ΛCDM) scenario for galaxy formation. This paper reviews these issues and considers the implications for cold versus various varieties of warm dark matter (WDM). The current evidence appears to be consistent with standard ΛCDM, although improving data may point toward a rather tepid version of ΛWDM—tepid since the dark matter cannot be very warm without violating observational constraints. (This is a substantially updated and expanded version of my talk at the DM08 meeting at Marina Del Rey, arXiv:0902.2506.)

Control of quantum phenomena has grown from a dream to a burgeoning field encompassing wide-ranging experimental and theoretical activities. Theoretical research in this area primarily concerns identification of the principles for controlling quantum phenomena, the exploration of new experimental applications and the development of associated operational algorithms to guide such experiments. Recent experiments with adaptive feedback control span many applications including selective excitation, wave packet engineering and control in the presence of complex environments. Practical procedures are also being developed to execute real-time feedback control considering the resultant back action on the quantum system. This focus issue includes papers covering many of the latest advances in the field.

Focus on Quantum Control Contents

Control of quantum phenomena: past, present and futureConstantin Brif, Raj Chakrabarti and Herschel Rabitz

Biologically inspired molecular machines driven by light. Optimal control of a unidirectional rotorGuillermo Pérez-Hernández, Adam Pelzer, Leticia González and Tamar Seideman

Simulating quantum search algorithm using vibronic states of I2 manipulated by optimally designed gate pulsesYukiyoshi Ohtsuki

Efficient coherent control by sequences of pulses of finite duration Götz S Uhrig and Stefano Pasini

Control by decoherence: weak field control of an excited state objective Gil Katz, Mark A Ratner and Ronnie Kosloff

Multi-qubit compensation sequences Y Tomita, J T Merrill and K R Brown

Environment-invariant measure of distance between evolutions of an open quantum system Matthew D Grace, Jason Dominy, Robert L Kosut, Constantin Brif and Herschel Rabitz

Simplified quantum process tomography M P A Branderhorst, J Nunn, I A Walmsley and R L Kosut

Achieving 'perfect' molecular discrimination via coherent control and stimulated emission Stephen D Clow, Uvo C Holscher and Thomas C Weinacht

A convenient method to simulate and visually represent two-photon power spectra of arbitrarily and adaptively shaped broadband laser pulses M A Montgomery and N H Damrauer

Accurate and efficient implementation of the von Neumann representation for laser pulses with discrete and finite spectra Frank Dimler, Susanne Fechner, Alexander Rodenberg, Tobias Brixner and David J Tannor

Coherent strong-field control of multiple states by a single chirped femtosecond laser pulse M Krug, T Bayer, M Wollenhaupt, C Sarpe-Tudoran, T Baumert, S S Ivanov and N V Vitanov

Quantum-state measurement of ionic Rydberg wavepackets X Zhang and R R Jones

On the paradigm of coherent control: the phase-dependent light-matter interaction in the shaping window Tiago Buckup, Jurgen Hauer and Marcus Motzkus

Use of the spatial phase of a focused laser beam to yield mechanistic information about photo-induced chemical reactions V J Barge, Z Hu and R J Gordon

Coherent control of multiple vibrational excitations for optimal detection S D McGrane, R J Scharff, M Greenfield and D S Moore

Mode selectivity with polarization shaping in the mid-IR David B Strasfeld, Chris T Middleton and Martin T Zanni

Laser-guided relativistic quantum dynamics Chengpu Liu, Markus C Kohler, Karen Z Hatsagortsyan, Carsten Muller and Christoph H Keitel

Continuous quantum error correction as classical hybrid control Hideo Mabuchi

Quantum filter reduction for measurement-feedback control via unsupervised manifold learning Anne E B Nielsen, Asa S Hopkins and Hideo Mabuchi

Control of the temporal profile of the local electromagnetic field near metallic nanostructures Ilya Grigorenko and Anatoly Efimov

Laser-assisted molecular orientation in gaseous media: new possibilities and applications Dmitry V Zhdanov and Victor N Zadkov

Optimization of laser field-free orientation of a state-selected NO molecular sample Arnaud Rouzee, Arjan Gijsbertsen, Omair Ghafur, Ofer M Shir, Thomas Back, Steven Stolte and Marc J J Vrakking

Controlling the sense of molecular rotation Sharly Fleischer, Yuri Khodorkovsky, Yehiam Prior and Ilya Sh Averbukh

Optimal control of interacting particles: a multi-configuration time-dependent Hartree-Fock approach Michael Mundt and David J Tannor

Exact quantum dissipative dynamics under external time-dependent driving fields Jian Xu, Rui-Xue Xu and Yi Jing Yan

Pulse trains in molecular dynamics and coherent spectroscopy: a theoretical study J Voll and R de Vivie-Riedle

Quantum control of electron localization in molecules driven by trains of half-cycle pulses Emil Persson, Joachim Burgdorfer and Stefanie Grafe

Quantum control design by Lyapunov trajectory tracking for dipole and polarizability coupling Jean-Michel Coron, Andreea Grigoriu, Catalin Lefter and Gabriel Turinici

Sliding mode control of quantum systems Daoyi Dong and Ian R Petersen

Implementation of fault-tolerant quantum logic gates via optimal control R Nigmatullin and S G Schirmer

Generalized filtering of laser fields in optimal control theory: application to symmetry filtering of quantum gate operations Markus Schroder and Alex Brown

We present a modified version of a previously published algorithm (Gollub et al 2008 Phys. Rev. Lett.101 073002) for obtaining an optimized laser field with more general restrictions on the search space of the optimal field. The modification leads to enforcement of the constraints on the optimal field while maintaining good convergence behaviour in most cases. We demonstrate the general applicability of the algorithm by imposing constraints on the temporal symmetry of the optimal fields. The temporal symmetry is used to reduce the number of transitions that have to be optimized for quantum gate operations that involve inversion (NOT gate) or partial inversion (Hadamard gate) of the qubits in a three-dimensional model of ammonia.

The implementation of fault-tolerant quantum gates on encoded logic qubits is considered. It is shown that transversal implementation of logic gates based on simple geometric control ideas is problematic for realistic physical systems suffering from imperfections such as qubit inhomogeneity or uncontrollable interactions between qubits. However, this problem can be overcome by formulating the task as an optimal control problem and designing efficient algorithms to solve it. In particular, we can find solutions that implement all of the elementary logic gates in a fixed amount of time with limited control resources for the five-qubit stabilizer code. Most importantly, logic gates that are extremely difficult to implement using conventional techniques even for ideal systems, such as the T-gate for the five-qubit stabilizer code, do not appear to pose a problem for optimal control.

This paper proposes a new robust control method for quantum systems with uncertainties involving sliding mode control (SMC). SMC is a widely used approach in classical control theory and industrial applications. We show that SMC is also a useful method for robust control of quantum systems. In this paper, we define two specific classes of sliding modes (i.e. eigenstates and state subspaces) and propose two novel methods combining unitary control and periodic projective measurements for the design of quantum SMC systems. Two examples including a two-level system and a three-level system are presented to demonstrate the proposed SMC method. One of the main features of the proposed method is that the designed control laws can guarantee the desired control performance in the presence of uncertainties in the system Hamiltonian. This SMC approach provides a useful control theoretic tool for robust quantum information processing with uncertainties.

In this paper we analyze the Lyapunov trajectory tracking of the Schrödinger equation for a coupling control operator containing both a linear (dipole) and a quadratic (polarizability) term. We show numerically that the contribution of the quadratic part cannot be exploited by standard trajectory tracking tools and propose two improvements: discontinuous feedback and periodic (time-dependent) feedback. For both cases we present theoretical results and support them by numerical illustrations.

We present numerical simulations demonstrating efficient control of electron localization dynamics in small molecular systems by a train of half-cycle pulses using the H₂⁺ molecule as a prototypical model system. Simulations are performed using a direct numerical integration of the Schrödinger equation on a grid for a two-degree of freedom system (one electronic, one nuclear coordinate) as well as for an expansion in terms of Born–Oppenheimer basis states. By varying the parameters of the driving field, we systematically explore the underlying control mechanism of this periodically approximately impulsively driven molecular system and demonstrate the robustness of the proposed control scheme.

Pulse trains (PTs) generated by sinusoidal phase masks emerged as a popular tool in the field of coherent control and have been applied successfully in many experiments. Although many attempts were made to throw light on the mechanism of the induced processes, it is not yet fully understood. Based on nonperturbative quantum dynamical calculations in the grid representation, we will elucidate the mechanism of PT excitation between anharmonic bound molecular electronic states. We extract general rules for the prediction of induced dynamics and the resulting spectra. The results allow us to outline perspectives for new applications, especially in the field of nonlinear spectroscopy.

An exact and nonperturbative quantum master equation can be constructed via the calculus on the path integral. It results in hierarchical equations of motion for the reduced density operator. Involved also are a set of well-defined auxiliary density operators that resolve not just the system–bath coupling strength but also memory. In this work, we scale these auxiliary operators individually to achieve a uniform error tolerance, as set by the reduced density operator. An efficient propagator is then proposed to the hierarchical Liouville-space dynamics of quantum dissipation. Numerically exact studies are carried out on the dephasing effect on population transfer in the simple stimulated Raman adiabatic passage scheme. We also make assessments on several perturbative theories for their applicabilities in the present system of study.

We combine optimal control theory with the multi-configuration time-dependent Hartree–Fock method to control the dynamics of interacting particles. We use the resulting scheme to optimize state-to-state transitions in a one-dimensional (1D) model of helium and to entangle the external degrees-of-freedom of two rubidium atoms in a 1D optical lattice. Comparisons with optimization results based on the exact solution of the Schrödinger equation show that the scheme can be used to optimize even involved processes in systems consisting of interacting particles in a reliable and efficient way.

We introduce a new scheme for controlling the sense of molecular rotation. By varying the polarization and the delay between two ultrashort laser pulses, we induce unidirectional molecular rotation, thereby forcing the molecules to rotate clockwise/counterclockwise under field-free conditions. We show that unidirectionally rotating molecules are confined to the plane defined by the two polarization vectors of the pulses, which leads to a permanent anisotropy in the molecular angular distribution. The latter may be useful for controlling collisional cross-sections and optical and kinetic processes in molecular gases. We discuss the application of this control scheme to individual components within a molecular mixture in a selective manner.

We present a theoretical investigation of the impulsive orientation that can be induced by exposing a sample of state-selected NO molecules to the combination of a dc field and a short laser pulse. A strong degree of laser-field-free alignment and orientation is already achievable at moderate intensities and can be further improved by tailoring the temporal profile of the laser pulse. The alignment and orientation are only limited by the maximum value of the applied dc field and the pulse energy in the femtosecond laser pulse. Using an evolutionary algorithm coupled to a non-perturbative calculation of the time-dependent Schrödinger equation, the solutions that are obtained suggest that ⟨cos θ⟩=0.964 is experimentally achievable.

It was shown recently by us that an isotropic distribution of molecules in gaseous media can be drastically effected via their orientation-dependent selective excitation by a strong femtosecond multicomponent laser pulse. In the present paper, we analyze the specific effects accompanying the dynamical orientation of molecules driven this way. It is demonstrated that the peculiarities of the post-pulse transient angular distribution of molecules allow original proposals for the generation of pulsed terahertz radiation and also for the determination of the molecular rotational constants.

We study control of the temporal profile of the local electric field in the vicinity of a small doped semiconductor or metal nanostructure. Unlike in the case of control in a gas or liquid phase, the collective response of electrons in the nanostructure may significantly enhance different frequency components of the external field. This enhancement strongly depends on the geometry of the nanostructure and can substantially modify the temporal profile of the local field. The changes in the amplitude and phase of the local field are studied using linear response theory within the random phase approximation. The inverse problem of finding the external electromagnetic field to generate an arbitrary target temporal profile of the local field, including the time-dependent polarization of the field, is considered and solved. We systematically study the pulse enhancement and shape distortion effects for a set of control pulses of various shapes.

We derive simple models for the dynamics of a single atom coupled to a cavity field mode in the absorptive bistable parameter regime by projecting the time evolution of the state of the system onto a suitably chosen nonlinear low-dimensional manifold, which is found by use of local tangent space alignment. The output field from the cavity is detected with a homodyne detector allowing observation of quantum jumps of the system between states with different average numbers of photons in the cavity. We find that the models, which are significantly faster to integrate numerically than the full stochastic master equation, largely reproduce the dynamics of the system, and we demonstrate that they are sufficiently accurate to facilitate feedback control of the state of the system based on the predictions of the models alone.

The standard formulation of quantum error correction (QEC) comprises repeated cycles of error estimation and corrective intervention in the free dynamics of a qubit register. QEC can thus be seen as a form of feedback control, and it is of interest to seek a deeper understanding of the connection between the associated theories. Here we present a focused case study within this broad program, connecting continuous QEC with elements of hybrid control theory. We show that canonical methods of the latter engineering discipline, such as recursive filtering and dynamic programming approaches to solving the optimal control problem, can be applied fruitfully in the design of separated controller structures for quantum memories based on coding and continuous syndrome measurement.

Super-strong short laser pulses are employed to accelerate electron quantum wave packets stemming from atoms and to guide them into recollision in spite of the magnetically induced relativistic drift motion. The recollision-induced processes of production of new particles and generation of high-frequency light are considered. We optimize the collisions by controlling the laser field polarization, the carrier–envelope phase and the beam focusing parameters.

We report that polarization-shaped mid-infrared (IR) pulses can be used to enhance the vibrational population of one mode over another in a coupled molecular system. A genetic algorithm and a new mid-IR polarization shaper were used to alter the relative vibrational excitation of the two carbonyl stretching modes in Mn(CO)₅Br. One mode could be selectively enhanced over the other by 2–3 times. Control over the polarization leads to better optimization than phase-only control. Several possible mechanisms that indicate how polarization shaping leads to selective vibrational excitation are discussed using a formalism that separates polarization shaping effects on the signal strength from amplitude or phase shaping. The techniques introduced herein will have broad applications in quantum gating schemes, controlling ground state chemistry and enhancing the sensitivity of multidimensional IR and visible spectroscopies.

While the means to selectively excite a single vibrational mode using ultrafast pulse shaping are well established, the subsequent problem of selectively exciting multiple vibrational modes simultaneously has been largely neglected. The coherent control of multiple vibrational excitations has applications in control of chemistry, chemical detection and molecular vibrational quantum information processing. Using simulations and experiments, we demonstrate that multiple vibrational modes can be selectively excited with the concurrent suppression of multiple interfering modes by orders of magnitude. While the mechanism of selectivity is analogous to that of single mode selectivity, the interferences required to select multiple modes require complicated non-intuitive pulse trains. Additionally, we show that selective detection can be achieved by the optimal pulse shape, even when the nature of the interfering species is varied, suggesting that optimized detection should be practical in real world applications. Experimental measurements of the multiplex coherent anti-Stokes Raman spectra (CARS) and CARS decay times of toluene, acetone, cis-stilbene and nitromethane liquids are reported, along with optimizations attempting to selectively excite nitromethane in a mixture of the four solvents. The experimental implementation exhibits a smaller degree of signal to background enhancement than predicted, which is primarily attributed to the single objective optimization methodology and not to fundamental limitations.

Two-pathway quantum mechanical interference was used to control the photoionization and photodissociation of a number of polyatomic molecules. The phase lag between different pairs of products obtained from acetone and dimethyl sulfide was altered by translating the focus of the laser beam along an axis normal to the molecular beam axis. This effect was derived quantitatively from the spatial Gouy phase of the laser beam. Details of the chemical reaction mechanisms were deduced from the channel phase lags, obtained when the laser was focused on the axis of the molecular beam, and from the variation of the phase lag produced by axial translation of the laser focus.

Coherent control is unquestioningly a powerful method to investigate the interaction of femtosecond light pulses with ultrafast molecular processes. In order to exploit to a great extent the capabilities of coherent control, a judicious analysis of experimental control results is required, which is especially true for the manipulation of matter waves with phase-locked femtosecond pulses. Due to its importance for the optical control of chemical reactions, we discuss the tailoring of wavepackets and the interpretation of such coherent control results in the region where the pump and probe pulses temporally overlap. In this region, called the shaping window, the observed dynamics are phase dependent and may misleadingly resemble oscillatory molecular dynamics. In a transient absorption experiment, part of these oscillations is successfully identified as intra-multipulse interferences and the phenomenon is qualitatively and quantitatively explained by the spectral appearance of the unshaped laser pulse. Furthermore a strategy is presented based on phase-cycling for easy differentiation between interference effects and true wavepacket dynamics. These new findings have important consequences for the interpretation of adaptive coherent control results.

Nearly unipolar, sub-picosecond half-cycle pulses (HCPs) have been used to measure, via impulsive ionization, the aspects of the electronic quantum state relevant to the radial motion of Ba⁺ ng Rydberg wavepackets. Following laser excitation of the ionic wavepacket, the double ionization probability is measured as a function of the amplitude and delay of the HCP probe. Fourier transform of the time-dependent ionization signal facilitates the determination of the complex amplitudes of the constituent ng eigenstates in the wavepacket, enabling a full characterization of its time-dependent radial evolution. This is the first experimental demonstration of wavepacket recovery in ions, a capability that may prove to be invaluable for future measurements of quantum dynamics in multielectron systems.

We present a joint experimental and theoretical study on strong-field photo-ionization of sodium atoms using chirped femtosecond laser pulses. By tuning the chirp parameter, selectivity among the population in the highly excited states 5p, 6p, 7p and 5f, 6f is achieved. Different excitation pathways enabling control are identified by simultaneous ionization and measurement of photoelectron angular distributions employing the velocity map imaging technique. Free electron wave packets at an energy of around 1 eV are observed. These photoelectrons originate from two channels. The predominant 2 + 1 + 1 resonance enhanced multi-photon ionization (REMPI) proceeds via the strongly driven two-photon transition 4s←←3s, and subsequent ionization from the states 5p, 6p and 7p whereas the second pathway involves 3 + 1 REMPI via the states 5f and 6f. In addition, electron wave packets from two-photon ionization of the non-resonant transiently populated state 3p are observed close to the ionization threshold. A mainly qualitative five-state model for the predominant excitation channel is studied theoretically to provide insights into the physical mechanisms at play. Our analysis shows that by tuning the chirp parameter the dynamics is effectively controlled by dynamic Stark shifts and level crossings. In particular, we show that under the experimental conditions the passage through an uncommon three-state 'bow-tie' level crossing allows the preparation of coherent superposition states.

We recently introduced the von Neumann picture, a joint time–frequency representation, for describing ultrashort laser pulses. The method exploits a discrete phase-space lattice of nonorthogonal Gaussians to represent the pulses; an arbitrary pulse shape can be represented on this lattice in a one-to-one manner. Although the representation was originally defined for signals with an infinite continuous spectrum, it can be adapted to signals with discrete and finite spectrum with great computational savings, provided that discretization and truncation effects are handled with care. In this paper, we present three methods that avoid loss of accuracy due to these effects. The approach has immediate application to the representation and manipulation of femtosecond laser pulses produced by a liquid-crystal mask with a discrete and finite number of pixels.

We report a convenient model of second harmonic (SH) spectra resulting from shaped laser fields created in pixilated pulse shaping devices based on a matrix of all possible pair-wise, field interactions. This model is useful in estimating simultaneous two-photon absorption (TPA) and second harmonic generation (SHG) cross sections. A simple geometric interpretation of the model allows for a graphical representation of the SH spectrum as a set of vectors in the complex plane. This interpretation can be used to illustrate the effects of applied phase (and amplitude) shaping on second-order observables and it provides a facile explanation of the spectral focusing mechanism observed in numerous control problems.