Critical experimental tests of the time-dependent Abraham force in phenomenological electrodynamics are scarce. In this paper, we analyze the possibility of making use of intensity-modulated whispering gallery modes in a microresonator for this purpose. Systems of this kind appear attractive, as the strong concentration of electromagnetic fields near the rim of the resonator serves to enhance the Abraham torque exerted by the field. We analyze mainly spherical resonators, although as an introductory step we consider also the cylinder geometry. The orders of magnitude of the Abraham torques are estimated by inserting reasonable and common values for the various input parameters. As expected, the predicted torques turn out to be very small, although probably not beyond reach experimentally. Our main idea is essentially a generalization of the method used by G. B. Walker et al. [Can. J. Phys. 53, 2577 (1975)] for low-frequency fields, to the optical case.

We consider two Jaynes-Cummings cavities coupled periodically with a photon hopping term. The semiclassical phase space is chaotic, with regions of stability over some ranges of the parameters. The quantum case exhibits dynamic localization and dynamic tunneling between classically forbidden regions. We explore the correspondence between the classical and quantum phase space and propose an implementation in a circuit QED system.

We study the spatial interference pattern of two-photon correlation function for a coherently phased linear array of $N$ emitters with a double-Raman scheme, each producing nonclassically correlated photon pairs. The $N^2$ dependence in the two-photon correlation serves as a coherent amplification method for producing intense nonclassical light. The spatial distribution of the correlation can be controlled by lasers, and depends on the detection configuration. For two coincident detectors, the nonclassical correlation displays the spatial Talbot pattern, but modulated by quantum interference effect. The image revival distance is found to be twice the usual Talbot length. For symmetrically located detectors ($X_1=-X_2$), the correlation displays a distorted Talbot pattern with intricate features and lack of symmetry.

We have computed the partial and total autoionization widths with interchannel coupling for the ${}^3{P}^o$ Wannier-ridge resonances of ${\mathrm{H}}^{-}$ below the $n=3$, 4, 5, 6, and 7 hydrogenic thresholds. The complex eigenvalue Schrödinger equations are solved using square-integrable wave functions with numerical and analytic real and complex orbitals. Trends regarding the decay dynamics and the excitation of high-orbital-angular-momentum electrons near threshold are established.

We calculate the nonadiabatic binding energy and geometry of the weakly bound state of $e^{+}$Na. We use the Peach model potential, which includes both the dipole and an effective quadrupole term in the polarization, to describe the interaction of the electron and positron with the ion core. The effective three-body Schrödinger equation is solved with the finite element method. Because the model potential gives rise to three spurious states, the true ground state of $e^{+}$Na is embedded in a dense spectrum of spurious states. We develop a method for extracting the correct ground state for $e^{+}$Na, even when the energy is nearly degenerate with a spurious level. The calculated value for the binding energy is consistent with other calculations.

The effects of Coulomb interaction screening on photodetachment cross sections of hydrogen negative ions below the $n$ $=2$ excitation threshold is investigated by using the $R$-matrix method with pseudostates. The contributions of Feshbach and shape resonances to ${\mathrm{H}}^{-}$ photodetachment cross section are presented when screening length ($D$) varies from $D$ $=$ $\infty$ to $D$ $=$ $4.6$ a.u. It is found that the interaction screening has dramatic effects on the photodetachment cross sections of hydrogen negative ions in the photoelectron energy region around the $n$ $=$ $2$ excitation threshold by strongly affecting the evolution of near-threshold resonances.

We study the dynamics of few interacting bosons in a one-dimensional lattice with dc bias. In the absence of interactions the system displays single-particle Bloch oscillations. For strong interaction the Bloch oscillation regime re-emerges with fractional Bloch periods which are inversely proportional to the number of bosons clustered into a bound state. The interaction strength affects the oscillation amplitude. Excellent agreement is found between numerical data and a composite particle dynamics approach. For specific values of the interaction strength, a particle will tunnel from the interacting cloud to a well-defined distant lattice location.

In a recent article, McGovern et al. [Phys. Rev. A 81, 042704 (2010)] suggested that the normalization of our measured fully differential cross section for ionization of helium by Au${}^{53+}$ needs to be checked. In this comment we confirm that the normalization of the published data is correct. Furthermore, we point out that, for a conclusive comparison between experiment and theory, an accurate inclusion of the experimental resolution using correct experimental parameters in the calculation is important.

In a recent paper, Wicht, Lämmerzahl, Lorek, and Dittus [Phys. Rev. A 78, 013610 (2008)] come to the conclusion that a molecular rotational-vibrational quantum interferometer may possess the sensitivity necessary to detect gravitational waves. We do not agree with their results and demonstrate here that the true sensitivity of such an interferometer is many orders of magnitude worse than that claimed in the paper.

We investigate several recently published benchmark criteria for storage or transmission of continuous-variable quantum information. A comparison reveals that criteria based on a Gaussian distribution of coherent states are most resilient to noise. We then address the issue of experimental resources and derive an equally strong benchmark, solely based on three coherent states and homodyne detection. This benchmark is further simplified in the presence of naturally occurring random phases, which remove the need for active input-state modulation.

Nondipolar corrections to the photoelectron angular distributions from ${\mathrm{C}}_{60}$ have been calculated for the highest occupied molecular orbital (HOMO), HOMO-1, and HOMO-2 photoemission bands. The computational method employed takes advantage of a parallel algorithm that uses a multicentric expansion of bound- and scattering-wave functions and a density-functional theory one-particle Hamiltonian. First-order nondipolar asymmetry parameters have been calculated from thresholds of up to 160 eV of photon energy. Strong oscillations, reminiscent of those found in the ratio of the HOMO and HOMO-1 partial cross sections, have been observed in the nondipolar asymmetry parameters as well. The oscillations have the same period, but a different phase, compared to the ones that characterize the HOMO-HOMO-$1$ intensity ratio.

We demonstrate a scheme for direct absorption imaging of an ultracold ground-state polar molecular gas near quantum degeneracy. Imaging molecules without closed optical cycling transitions is challenging. Our technique relies on photon-shot-noise-limited absorption imaging on a strong but open bound-bound molecular transition. We present a systematic characterization of this imaging technique. Using this technique combined with time-of-flight expansion, we demonstrate the capability to determine momentum and spatial distributions for the molecular gas. With its capability of imaging molecules in arbitrary external fields, we anticipate that this technique will find many applications in the study of molecular quantum gases.

We theoretically investigate and demonstrate a better wavelength scaling of harmonic yield in a two-color infrared field. By mixing a Ti:sapphire assistant field with the infrared driving field, we show that high harmonic generation is enhanced and the harmonic yield scales as ${\lambda }^{-3}$–${\lambda }^{-4}$ in the plateau region, which falls more slowly as the increase of the driving laser wavelength $\lambda$ compared with ${\lambda }^{-5}$–${\lambda }^{-6}$ in a one-color infrared field.

We study the dynamics of pure phase decoherence for a particle hopping around an $N$-site ring, coupled both to a spin bath and to an Aharonov-Bohm flux which threads the ring. Analytic results are found for the dynamics of the influence functional and of the reduced density matrix of the particle, both for initial single wave-packet states, and for states split initially into two separate wave packets moving at different velocities. We also give results for the dynamics of the current as a function of time.

The violation of uncertainty relations is used as a signature of entanglement for both pure and mixed states of two identical fermions. In the case of fermions with a four-dimensional single-particle Hilbert space we obtain several different types of uncertainty-related entanglement criteria based on local uncertainty relations, on the sum of variances of projectors, and on various entropic measures. Within the latter approach we consider either entropic uncertainty relations involving a single observable or relations based upon the sum of entropies associated with more than one observable. We extend the projector-based entanglement criterion to the case of two-fermion and three-fermion systems with a six-dimensional single-particle Hilbert space.

We introduce a scheme for secure multiparty computation utilizing the quantum correlations of entangled states. First we present a scheme for two-party computation, exploiting the correlations of a Greenberger-Horne-Zeilinger state to provide, with the help of a third party, a near-private computation scheme. We then present a variation of this scheme which is passively secure with threshold $t=2$, in other words, remaining secure when pairs of players conspire together provided they faithfully follow the protocol. Furthermore, we show that the passively secure variant can be modified to be secure when cheating parties are allowed to deviate from the protocol. We show that this can be generalized to computations of $n$-party polynomials of degree 2 with a threshold of $n-1$. The threshold achieved is significantly higher than the best known classical threshold, which satisfies the bound $t<n/2$. Our schemes, each complying with a different definition of security, shed light on which physical assumptions are necessary in order to achieve quantum secure multiparty computation.

We consider the representation of operators in terms of tensor networks and their application to the ground-state approximation and time evolution of systems with long-range interactions. We provide an explicit construction to represent an arbitrary many-body Hamilton operator in terms of a one-dimensional tensor network (i.e., as a matrix product operator). For pairwise interactions, we show that such a representation is always efficient and requires a tensor dimension growing only linearly with the number of particles. For systems obeying certain symmetries or restrictions we find optimal representations with minimal tensor dimension. We discuss the analytic and numerical approximation of operators in terms of low-dimensional tensor operators. We demonstrate applications for time evolution and the ground-state approximation, in particular for long-range interaction with inhomogeneous couplings. The operator representations are also generalized to other geometries such as trees and two-dimensional lattices, where we show how to obtain and use efficient tensor network representations respecting a given geometry.

We investigate quantum measurement strategies capable of discriminating two coherent states probabilistically with significantly smaller error probabilities than can be obtained using nonprobabilistic state discrimination. We apply a postselection strategy to the measurement data of a homodyne detector as well as a photon number resolving detector in order to lower the error probability. We compare the two different receivers with an optimal intermediate measurement scheme where the error rate is minimized for a fixed rate of inconclusive results. The photon number resolving (PNR) receiver is experimentally demonstrated and compared to an experimental realization of a homodyne receiver with postselection. In the comparison, it becomes clear that the performance of the PNR receiver surpasses the performance of the homodyne receiver, which we prove to be optimal within any Gaussian operations and conditional dynamics.

We report how quantum information encoded into the spectral degree of freedom of a single-photon state may be teleported using a finite spectrally entangled biphoton state. We further demonstrate how the bandwidth of the teleported wave form can be controllably and coherently dilated using a spread-spectral variant of teleportation. We calculate analytical expressions for the fidelities of spectral and spread-spectral teleportation when complex-valued Gaussian states are transferred using a proposed experimental approach. Finally, we discuss the utility of these techniques for integrating broad-bandwidth photonic qubits with narrow-bandwidth receivers in quantum communication systems.

Quantum walk models have been used as an algorithmic tool for quantum computation and to describe various physical processes. This article revisits the relationship between relativistic quantum mechanics and the quantum walks. We show the similarities of the mathematical structure of the decoupled and coupled forms of the discrete-time quantum walk to that of the Klein-Gordon and Dirac equations, respectively. In the latter case, the coin emerges as an analog of the spinor degree of freedom. Discrete-time quantum walk as a coupled form of the continuous-time quantum walk is also shown by transforming the decoupled form of the discrete-time quantum walk to the Schrödinger form. By showing the coin to be a means to make the walk reversible and that the Dirac-like structure is a consequence of the coin use, our work suggests that the relativistic causal structure is a consequence of conservation of information. However, decoherence (modeled by projective measurements on position space) generates entropy that increases with time, making the walk irreversible and thereby producing an arrow of time. The Lieb-Robinson bound is used to highlight the causal structure of the quantum walk to put in perspective the relativistic structure of the quantum walk, the maximum speed of walk propagation, and earlier findings related to the finite spread of the walk probability distribution. We also present a two-dimensional quantum walk model on a two-state system to which the study can be extended.