We describe the implementation of laser-cooled silica microspheres as force sensors in a dual-beam optical dipole trap in high vacuum. Using this system we have demonstrated trap lifetimes exceeding several days, attonewton force detection capability, and wide tunability in trapping and cooling para...

[Phys. Rev. A 91, 051805(R)] Published Tue May 26, 2015

]]>Multipartite nonlocality is of great fundamental interest and constitutes a useful resource for many quantum information protocols. However, demonstrating it in practice, by violating a Bell inequality, can be difficult. In particular, standard experimental setups require the alignment of distant pa...

[Phys. Rev. A 91, 052118] Published Tue May 26, 2015

]]>Beginning with the principle that a closed mechanical composite system is timeless, time can be defined by the regular changes in a suitable position coordinate (clock) in the observing part, when one part of the closed composite observes another part. Translating this scenario into both classical a...

[Phys. Rev. A 91, 052119] Published Tue May 26, 2015

]]>Quantum information can be encoded in the set of steady states (SSS) of a driven-dissipative system. Nonsteady states are separated by a large dissipative gap that adiabatically decouples them while the dynamics inside the SSS is governed by an effective, dissipation-projected, Hamiltonian. The latt...

[Phys. Rev. A 91, 052324] Published Tue May 26, 2015

]]>A possible setup for a quantum-repeater network using satellite links is demonstrated, and it is shown that this approach allows entanglement creation at viable rates over global distances that are inaccessible via direct transmission through optical fibers.

[Phys. Rev. A 91, 052325] Published Tue May 26, 2015

]]>We discuss the so-called mean king's problem, a retrodiction problem among noncommutative observables, in the context of error detection. Describing the king's measurement effectively by a single error operation, we give a solution of the mean king's problem using quantum error-correcting codes. The...

[Phys. Rev. A 91, 052326] Published Tue May 26, 2015

]]>Universal quantum simulation may provide insights into those many-body systems that cannot be described classically and that cannot be efficiently simulated with current technology. The Trotter formula, which decomposes a desired unitary time evolution of the simulator into a stroboscopic sequence o...

[Phys. Rev. A 91, 052327] Published Tue May 26, 2015

]]>A recently demonstrated technique of continuous indirect pumping enables a high level of atomic spin polarization to be generated in thermal alkali-metal vapors, without compromising the coherence lifetime through power broadening from the pump laser. The indirect pumping process combines optical ex...

[Phys. Rev. A 91, 053419] Published Tue May 26, 2015

]]>We report the achievement of stimulated Raman adiabatic passage (STIRAP) in the microwave frequency range between internal states of a Bose-Einstein condensate magnetically trapped in the vicinity of an atom chip. The STIRAP protocol used in this experiment is robust to external perturbations as it ...

[Phys. Rev. A 91, 053420] Published Tue May 26, 2015

]]>We present an experimental investigation of ultrafast laser-driven Rabi oscillations of atomic rubidium. Because the broadband spectrum of an ultrafast laser pulse simultaneously couples all of the electronic hyperfine transitions between the excited and ground states, the complex excitation linkage...

[Phys. Rev. A 91, 053421] Published Tue May 26, 2015

]]>Photoionization cross sections and dipole angular distribution asymmetry parameters, β, of $5s$ and $4d$ shells of the closed-shell ions $({\mathrm{La}}^{3+},{\mathrm{La}}^{9+}$, and ${\mathrm{La}}^{11+})$ in the La isonuclear sequence have been studied using the relativistic random phase approximation. The positions of the $5s$ Cooper minima in ${\mathrm{La}}^{3+}$...

[Phys. Rev. A 91, 053422] Published Tue May 26, 2015

]]>Thanks to the recent experimental realization and control of artificial gauge fields, spin-orbit (SO) couplings are witnessing an ever increasing interest in the field of cold atoms. However, predicting their effect on spin polarization and energetic properties of interacting systems is a major chal...

[Phys. Rev. A 91, 053622] Published Tue May 26, 2015

]]>A trapped atom interferometer involving state-selective adiabatic potentials with two microwave frequencies on a chip is proposed. We show that this configuration provides a way to achieve a high degree of symmetry between the two arms of the interferometer, which is necessary for coherent splitting...

[Phys. Rev. A 91, 053623] Published Tue May 26, 2015

]]>We present a variational study of pseudo-spin-$1/2$ Bose gases in a harmonic trap with weak three-dimensional (3D) spin-orbit coupling of $\mathbf{\sigma}\xb7\mathbf{p}$ type. This spin-orbit coupling mixes states with different parities, which inspires us to approximate the single-particle state with the eigenstates of the tota...

[Phys. Rev. A 91, 053624] Published Tue May 26, 2015

]]>The dynamics of a single impurity interacting with a many-particle background is one of the central problems of condensed-matter physics. Recent progress in ultracold-atom experiments makes it possible to control this dynamics by coupling an artificial gauge field specifically to the impurity. In th...

[Phys. Rev. A 91, 053625] Published Tue May 26, 2015

]]>We show that the description of light in terms of Stokes operators in combination with the assumption of Gaussian statistics results in a dramatic simplification of the experimental study of fluctuations in the light transmitted through an atomic vapor: no local oscillator is required, the detected ...

[Phys. Rev. A 91, 053848] Published Tue May 26, 2015

]]>A proposal is presented for the optomechanical levitation of objects with enhanced isolation from the environment, which is of practical interest for a variety of applications ranging from frequency-tuned high-resolution force sensing to quantum optomechanics experiments.

[Phys. Rev. A 91, 053849] Published Tue May 26, 2015

]]>Nonlinear quantum optical systems are of paramount relevance for modern quantum technologies, as well as for the study of dissipative phase transitions. Their nonlinear nature makes their theoretical study very challenging and hence they have always served as great motivation to develop new techniqu...

[Phys. Rev. A 91, 053850] Published Tue May 26, 2015

]]>Methods for precisely resolving the continuous-variable energy-time entanglement of paired photons have always been sought in quantum optics. The Fabry-Pérot interferometer provides such a distinguished opportunity if the single-photon pulse's self-interference is carefully avoided. A dual-channel F...

[Phys. Rev. A 91, 053851] Published Tue May 26, 2015

]]>M. Pirbhai *et al.* [Phys. Rev. A **88**, 060701(R) (2013)] reported a new optically pumped spin-exchange polarized-electron source developed to avoid the limitations of the traditional GaAs-type source and to enable a broader range of experiments. The spin-exchange gaseous source has introduced its own l...

[Phys. Rev. A 91, 056703] Published Tue May 26, 2015

]]>In this Reply, we respond to the above Comment.

[Phys. Rev. A 91, 056704] Published Tue May 26, 2015

]]>[Phys. Rev. A 91, 059904] Published Tue May 26, 2015

]]>[Phys. Rev. A 91, 059905] Published Tue May 26, 2015

]]>Enhanced nonlinear optical response of a coherent atomic medium is the basis for many atomic sensors, and their performance is ultimately limited by the quantum fluctuations of the optical readout. Here we demonstrate that the off-resonant interactions, with the aid of the near-resonant process, can...

[Phys. Rev. A 91, 051804(R)] Published Fri May 22, 2015

]]>Quantum coherence is a key element in topical research on quantum resource theories and a primary facilitator for design and implementation of quantum technologies. However, the resourcefulness of quantum coherence is severely restricted by environmental noise, which is indicated by the loss of info...

[Phys. Rev. A 91, 052115] Published Fri May 22, 2015

]]>We address the question of locality versus nonlocality in the Aharonov-Bohm and the Aharonov-Casher effects. For this purpose, we investigate all possible configurations of ideal shielding of the overlap between the electromagnetic fields generated by a charge and by a magnetic flux and analyze thei...

[Phys. Rev. A 91, 052116] Published Fri May 22, 2015

]]>We investigate the geometric phase for a quantum field driven by an external source and subjected to spontaneous decay from coupling to the reservoir. Starting from a coherent state, we analyze the effect of decoherence when the system undergoes a nonadiabatic cyclic evolution in phase space, and sh...

[Phys. Rev. A 91, 052117] Published Fri May 22, 2015

]]>Many important computer science problems can be reduced to the clause-satisfaction problem. We are given $n$ Boolean variables ${x}_{k}$ and $m$ clauses ${c}_{j}$ where each clause is a function of values of some ${x}_{k}$. We want to find an assignment $i$ of ${x}_{k}$ for which all $m$ clauses are satisfied. Let ${f}_{j}\left(i\right)$ be a binary fu...

[Phys. Rev. A 91, 052322] Published Fri May 22, 2015

]]>A method is introduced to realize dispersion-free transport of a localized wave packet on a lattice by devising a Hamiltonian so that the wave packet perfectly splits and interferes with itself, providing a new avenue in the field of perfect state transfer.

[Phys. Rev. A 91, 052323] Published Fri May 22, 2015

]]>On top of the mean-field analysis of a Bose-Einstein condensate, one typically applies the Bogoliubov theory to analyze quantum fluctuations of the excited modes. Therefore, one has to diagonalize the Bogoliubov Hamiltonian in a symplectic manner. In our article we investigate the topology of these ...

[Phys. Rev. A 91, 053621] Published Fri May 22, 2015

]]>The tight confinement of the evanescent light field around the waist of an optical nanofiber makes it a suitable tool for studying nonlinear optics in atomic media. Here, we use an optical nanofiber embedded in a cloud of laser-cooled ${}^{87}\mathrm{Rb}$ for near-infrared frequency up-conversion via a resonant two...

[Phys. Rev. A 91, 053842] Published Fri May 22, 2015

]]>We use theoretical analysis and numerical simulation to investigate the operation of a laser oscillating from gain supplied by stimulated Brillouin scattering (SBS) in a microresonator. The interaction of the forward, backward, and density waves within the microresonator results in a set of coupled-...

[Phys. Rev. A 91, 053843] Published Fri May 22, 2015

]]>Quantum optical fields offer numerous control knobs which are not available with classical light and may be used for monitoring the properties of matter by novel types of spectroscopy. It has been recently argued that such quantum spectroscopy signals can be obtained by a simple averaging of their c...

[Phys. Rev. A 91, 053844] Published Fri May 22, 2015

]]>We study two-level systems (2LS) coupled at different points to a one-dimensional waveguide in which one end is open and the other is either open (infinite waveguide) or closed by a mirror (semi-infinite). Upon injection of two photons (corresponding to weak coherent driving), the resonance fluoresc...

[Phys. Rev. A 91, 053845] Published Fri May 22, 2015

]]>The propagation of light in a resonant atomic vapor can *a priori* be thought of as a multiple scattering process, in which each scattering event redistributes both the direction and the frequency of the photons. Particularly, the frequency redistribution may result in Lévy flights of photons, directl...

[Phys. Rev. A 91, 053846] Published Fri May 22, 2015

]]>We study the propagation of guided light along an array of three-level atoms in the vicinity of an optical nanofiber under the condition of electromagnetically induced transparency. We examine two schemes of atomic levels and field polarizations where the guided probe field is quasilinearly polarize...

[Phys. Rev. A 91, 053847] Published Fri May 22, 2015

]]>We studied alignment-to-orientation conversion caused by excited-state level crossings in a nonzero magnetic field of both atomic rubidium isotopes. Experimental measurements were performed on the transitions of the ${D}_{2}$ line of rubidium. These measured signals were described by a theoretical model th...

[Phys. Rev. A 91, 053418] Published Thu May 21, 2015

]]>We theoretically and numerically study Bogoliubov-wave turbulence in three-dimensional atomic Bose-Einstein condensates with the Gross-Pitaevskii equation, investigating three spectra for the macroscopic wave function, the density distribution, and the Bogoliubov-wave distribution. In this turbulenc...

[Phys. Rev. A 91, 053620] Published Thu May 21, 2015

]]>Despite its unique capability of distinguishing molecular handedness, chiroptical spectroscopy suffers from the weak-signal problem, which has restricted more extensive applications. The quasi-null-polarization-detection (QNPD) method has been shown to be useful for enhancing the chiroptical signal....

[Phys. Rev. A 91, 053839] Published Thu May 21, 2015

]]>Nondiffractive Bessel beams are well known to have infinite energy and infinite orbital angular momentum (OAM). However, when normalized to unity of energy, their OAM is finite. In this work, we derive an analytical relationship for calculating the normalized OAM of the superposition of off-axis Bes...

[Phys. Rev. A 91, 053840] Published Thu May 21, 2015

]]>The spectrum of the second harmonic signal generated in quadratic nonlinear photonic crystals, having different types of edge dislocations, was studied theoretically and experimentally. In the case of a dislocation with a fractional topological charge, we observed an asymmetric spectral conversion e...

[Phys. Rev. A 91, 053841] Published Thu May 21, 2015

]]>The possibility to control charge migration in molecules using femtosecond laser pulses is studied, which may have applications in the laser control of fundamental chemical processes.

[Phys. Rev. A 91, 051401(R)] Published Wed May 20, 2015

]]>We introduce a nanowire-based photonic-crystal waveguide system capable of controllably mediating the photon coupling between two quantum dots which are macroscopically separated. Using a rigorous Green-function-based master equation approach, our two-dot system is shown to provide a wide range of i...

[Phys. Rev. A 91, 051803(R)] Published Wed May 20, 2015

]]>We show that any finite quantum system $S$ can be coupled to a dephasing environment in such a way that the internal mechanism responsible for relaxation of observables acting on $S$ can be effectively canceled. By adjusting this coupling, the difference between the initial and the long–time expectation...

[Phys. Rev. A 91, 052112] Published Wed May 20, 2015

]]>We discuss the prospect of $\mathcal{PT}$-symmetric Hamiltonians finding applications in quantum information science, and conclude that such evolution is unlikely to provide any benefit over existing techniques. Although it has been known for some time that $\mathcal{PT}$-symmetric quantum theory, when viewed as a unitary ...

[Phys. Rev. A 91, 052113] Published Wed May 20, 2015

]]>We propose and theoretically simulate an experiment for demonstrating a motional-state Bell inequality violation for pairs of momentum-entangled atoms produced in Bose-Einstein condensate collisions. The proposal is based on realizing an atom-optics analog of the Rarity-Tapster optical scheme: it us...

[Phys. Rev. A 91, 052114] Published Wed May 20, 2015

]]>A crucial property of quantum networks is the entanglement between different network nodes. We demonstrate that entanglement in quantum networks can be created and controlled by introducing quantum-coherent time-delayed self-feedback at single nodes.

[Phys. Rev. A 91, 052321] Published Wed May 20, 2015

]]>In this work we obtain analytical expressions for the nonadditivity effects in the dispersive interaction between two atoms and a perfectly conducting surface of arbitrary shape in the nonretarded regime. We show that this three-body quantum-mechanical problem can be solved by mapping it onto a two-...

[Phys. Rev. A 91, 052708] Published Wed May 20, 2015

]]>We determine the ground-state energy and Tan's contact of attractively interacting few-fermion systems in a one-dimensional harmonic trap, for a range of couplings and particle numbers. Complementing those results, we show the corresponding density profiles. The calculations were performed with a la...

[Phys. Rev. A 91, 053618] Published Wed May 20, 2015

]]>We investigate the properties of a homogeneous dipolar Bose gas in a weak three-dimensional isotropic speckle disorder at finite temperatures. By using the Bogoliubov theory (beyond the mean field), we calculate the condensate and the superfluid fractions as a function of density and strengths of di...

[Phys. Rev. A 91, 053619] Published Wed May 20, 2015

]]>We investigate the response of a polariton laser driven slightly off-resonantly using light fields differing from the routinely studied coherent pump sources. The response to driving light fields with thermal and displaced thermal statistics with varying correlation times shows significant differenc...

[Phys. Rev. A 91, 053835] Published Wed May 20, 2015

]]>We present an approach for the description of fluorescence from optically active materials embedded in layered periodic structures. Based on an exact electromagnetic Green's tensor analysis, we determine the radiative properties of emitters such as the local photonic density of states, Lamb shifts, ...

[Phys. Rev. A 91, 053836] Published Wed May 20, 2015

]]>We report generation of a broadband supercontinuum (SC) in a birefringent crystal upon irradiation by intense, near-infrared, femtosecond laser pulses and investigate its dependence on incident laser power and the initial laser polarization. We choose as our sample $\alpha -{\mathrm{BaB}}_{2}{\mathrm{O}}_{4}$ ($\alpha $-BBO), a material in wh...

[Phys. Rev. A 91, 053837] Published Wed May 20, 2015

]]>In a previous publication, we showed how group actions can be used to generate Bell inequalities. The group action yields a set of measurement probabilities whose sum is the basic element in the inequality. The sum has an upper bound if the probabilities are a result of a local, realistic theory, bu...

[Phys. Rev. A 91, 052110] Published Tue May 19, 2015

]]>We introduce two families of sum-of-squares (SOS) decompositions for the Bell operators associated with the tilted Clauser-Horne-Shimony-Holt (CHSH) expressions introduced in Acín *et al.* [Phys. Rev. Lett. **108**, 100402 (2012)]. These SOS decompositions provide tight upper bounds on the maximal quantum...

[Phys. Rev. A 91, 052111] Published Tue May 19, 2015

]]>We present a cavity dissipation scheme to prepare a hybrid system of an atomic ensemble and a moving mirror in squeezed and entangled states. This scheme is based on four-wave mixing in the atoms and radiation pressure on the mirror, both of which combine to lead to Bogoliubov interactions of the at...

[Phys. Rev. A 91, 052320] Published Tue May 19, 2015

]]>We take a closer look at the fundamental Casimir-Polder (CP) interaction between quantum particles and dispersive dielectric surfaces with surface polariton or plasmon resonances. Linear response theory shows that in the near-field, van der Waals regime the free-energy shift of a particle contains a...

[Phys. Rev. A 91, 052506] Published Tue May 19, 2015

]]>Dispersion interactions such as the van der Waals interaction between atoms or molecules derive from quantum fluctuations of the electromagnetic field and can be understood as the exchange of virtual photons between the interacting partners. Any modification of the environment in which those photons...

[Phys. Rev. A 91, 052707] Published Tue May 19, 2015

]]>The effects induced during the process of inner-shell photoionization followed by Auger decay are investigated for the photoionization of Kr $3{d}_{5/2}$ in an extremely low photoelectron energy regime. Both the photoelectron energy and relative angular distributions are calculated with a recently develope...

[Phys. Rev. A 91, 053416] Published Tue May 19, 2015

]]>We develop the eikonal perturbation theory to describe the strong-field ionization by finite laser pulses. This approach in the first order with respect to the binding potential (the so-called generalized eikonal approximation) avoids a singularity at the potential center. Thus, in contrast to the o...

[Phys. Rev. A 91, 053417] Published Tue May 19, 2015

]]>We investigate the nonlinear optical features of a graphene sheet embedded in an active cavity and we show that, when tuned near its lasing threshold, the cavity is able to isolate the spatially localized graphene nonlinearity thus producing a very strong nonlinear device response with multivalued f...

[Phys. Rev. A 91, 053833] Published Tue May 19, 2015

]]>We apply a simple analytical method based on a unitary transformation to calculate the Bloch-Siegert (BS) shift over the entire driving-strength range. In quantitative comparison with the numerically exact BS shift obtained by Floquet formalism as well as the previous BS results, we confirm that our...

[Phys. Rev. A 91, 053834] Published Tue May 19, 2015

]]>The direct state measurement (DSM) based on the weak measurement has the advantage of simplicity, versatility, and directness. However, the weak measurement will introduce an unavoidable error in the reconstructed quantum state. We modify the DSM by replacing the weak coupling between the system and...

[Phys. Rev. A 91, 052109] Published Mon May 18, 2015

]]>Repeat-until-success (RUS) circuits can approximate a given single-qubit unitary with an expected number of $T$ gates of about $\frac{1}{3}$ of what is required by optimal, deterministic, ancilla-free decompositions over the Clifford + $T$ gate set. In this work, we introduce a more general and conceptually simple...

[Phys. Rev. A 91, 052317] Published Mon May 18, 2015

]]>Time-reversal symmetry breaking can enhance or suppress the probability of success for quantum state transfer (QST), and remarkably it can be used to implement the directional QST. In this paper we study the QST on a ring with time-reversal asymmetry. We show that the system will behave as a quantum...

[Phys. Rev. A 91, 052318] Published Mon May 18, 2015

]]>A coinless, discrete-time quantum walk possesses a Hilbert space whose dimension is smaller compared to the widely studied coined walk. Coined walks require the direct product of the site basis with the coin space; coinless walks operate purely in the site basis, which is clearly minimal. These coin...

[Phys. Rev. A 91, 052319] Published Mon May 18, 2015

]]>We use the perturbed relativistic coupled-cluster (PRCC) theory to compute the electric dipole polarizabilities $\alpha $ of Zn, Cd, and Hg. The computations are done using the Dirac-Coulomb-Breit Hamiltonian with the Uehling potential to incorporate vacuum polarization corrections. To assimilate the self-e...

[Phys. Rev. A 91, 052504] Published Mon May 18, 2015

]]>A collisional inhomogeneous broadening of the ${\text{H}}_{2}$ $Q\left(1\right)$ line perturbed by Ar was observed for the first time 25 years ago. Several attempts were made to explain the line broadening from *ab initio* calculations, which, however, resulted in fundamental discrepancies between the theory and experiment. To ...

[Phys. Rev. A 91, 052505] Published Mon May 18, 2015

]]>The ability to coherently rearrange structures at the atomic scale is among the grand challenges of physical science. Some of the primary obstacles are nonadiabatic increases in energy, such as intramolecular vibrational relaxation (IVR) and electronic excitations. Motivated by recent advances in st...

[Phys. Rev. A 91, 052706] Published Mon May 18, 2015

]]>We solve the problem of tunneling ionization of a multielectron atom in a static electric field by using the Green's function for the Stark-Coulomb problem. This allows us to incorporate the outgoing-wave boundary conditions at infinity. The interaction of the active electron with the atomic residue...

[Phys. Rev. A 91, 053412] Published Mon May 18, 2015

]]>Electron correlation can break the symmetry of photoelectron angular distribution upon two-step ionization to a doubly degenerate ionic state via a doubly degenerate intermediate state. The interference between the two components of the intermediate state prepared using linearly and circularly polar...

[Phys. Rev. A 91, 053413] Published Mon May 18, 2015

]]>In situ fluorescence detection of atoms in a dipole trap using a blue-detuned probe beam in addition to the standard cooling laser beams is demonstrated, and it is shown that atom numbers up to about 100 can be detected with sub-Poissonian precision.

[Phys. Rev. A 91, 053414] Published Mon May 18, 2015

]]>Initial insight into time delay in Mn photoionization in the region of the $3p\phantom{\rule{0.16em}{0ex}}\to ,3d$ giant autoionization resonance is gained in the framework of the “spin-polarized” random-phase approximation with exchange. The dramatic effect of the giant autoionization resonance on the time delay of photoemission f...

[Phys. Rev. A 91, 053415] Published Mon May 18, 2015

]]>A Ramsey-Raman interferometer is used to realize a compact force sensor using cold ${}^{87}\mathrm{Rb}$ atoms trapped in a vertical optical lattice. The sensitivity and accuracy of the force measurements are discussed and the limits in short-term sensitivity evaluated. We reach a relative sensitivity on the Bloch f...

[Phys. Rev. A 91, 053616] Published Mon May 18, 2015

]]>We demonstrate the realization of topological band structures by exploiting the intrinsic spin-orbit coupling of dipolar interactions in combination with broken time-reversal symmetry. The system is based on polar molecules trapped in a deep optical lattice, where the dynamics of rotational excitati...

[Phys. Rev. A 91, 053617] Published Mon May 18, 2015

]]>Intensity- and phase-noise correlations in a dual-frequency VECSEL are studied theoretically and experimentally, and it is shown how the results can be interpreted in terms of the linear response of two coupled overdamped oscillators.

[Phys. Rev. A 91, 053828] Published Mon May 18, 2015

]]>Polarizable particles trapped in a resonator-sustained optical-lattice potential generate strong position-dependent backaction on the intracavity field. In the quantum regime, particles in different energy bands are connected to different intracavity light intensities and optical-lattice depths. Thi...

[Phys. Rev. A 91, 053829] Published Mon May 18, 2015

]]>Recently, we have demonstrated that second-order subwavelength interference could be realized in an optical lithography scheme with an effective entangled source [P. Hong and G. Zhang, Phys. Rev. A **88**, 043838 (2013)]. In this paper, by considering the correlation function in both the source plane an...

[Phys. Rev. A 91, 053830] Published Mon May 18, 2015

]]>The emergence of optical micro- or nanofibers (MNFs) with subwavelength diameter, which have ultralight mass and an intense light field, provides an opportunity for developing fiber-based optomechanical systems. In this study we show theoretically an optomechanical effect in silica MNF Bragg grating...

[Phys. Rev. A 91, 053831] Published Mon May 18, 2015

]]>It is generally difficult to study the dynamical properties of a quantum system with both inherent quantum noises and nonperturbative nonlinearity. Due to the possibly drastic intensity increase of an input coherent light in gain-loss waveguide couplers with parity-time $\left(\mathcal{PT}\right)$ symmetry, the Kerr effec...

[Phys. Rev. A 91, 053832] Published Mon May 18, 2015

]]>We propose a practical quantum cryptographic scheme which combines high information capacity, such as provided by high-dimensional quantum entanglement, with the simplicity of a two-dimensional Clauser-Horne-Shimony-Holt (CHSH) Bell test for security verification. By applying a state combining entan...

[Phys. Rev. A 91, 052313] Published Fri May 15, 2015

]]>In the $4\otimes 4$ quantum system, four qubit lattice states are found to be either locally indistinguishable or distinguishable by using one-way classical communication only, presenting a curious and counterintuitive case in which two-way classical communication has no advantage. Based on these results, we...

[Phys. Rev. A 91, 052314] Published Fri May 15, 2015

]]>A negatively charged nitrogen-vacancy (NV) center in diamond has been recognized as a good solid-state qubit. A system consisting of the electronic spin of the NV center and hyperfine-coupled nitrogen and additionally nearby carbon nuclear spins can form a quantum register of several qubits for quan...

[Phys. Rev. A 91, 052315] Published Fri May 15, 2015

]]>Nonselective quantum measurements, i.e., measurements without reading the results, are often considered as a resource for manipulating quantum systems. In this work, we investigate optimal acceleration of the Landau-Zener (LZ) transitions by nonselective quantum measurements. We use the measurements...

[Phys. Rev. A 91, 052316] Published Fri May 15, 2015

]]>We describe a theoretical approach to molecular photoionization that includes first-order corrections to the dipole approximation. The theoretical formalism is presented and applied to photoionization of ${\mathrm{H}}_{2}$ over the 20- to 180-eV photon energy range. The angle-integrated cross section $\sigma $, the electri...

[Phys. Rev. A 91, 053410] Published Fri May 15, 2015

]]>We investigate the dynamics under diabatic expansions or compressions of linear ion chains. Combining a dynamical normal-mode harmonic approximation with the invariant-based inverse-engineering technique, we design protocols that minimize the final motional excitation of the ions. This can substanti...

[Phys. Rev. A 91, 053411] Published Fri May 15, 2015

]]>We propose a scheme for spin squeezing in the orbital motion of a Bose-Einstein condensate in a toroidal trap. A circular lattice couples two counterrotating modes and squeezing is generated by the nonlinear interaction spatially modulated at half the lattice period. By varying the amplitude and pha...

[Phys. Rev. A 91, 053612] Published Fri May 15, 2015

]]>We demonstrate that measurements of number fluctuations within finite cells provide a direct means to study susceptibility scaling in a trapped two-component Bose-Einstein condensate. This system supports a second-order phase transition between miscible (cospatial) and immiscible (symmetry-broken) s...

[Phys. Rev. A 91, 053613] Published Fri May 15, 2015

]]>We perform a comparative beyond-mean-field study of black and gray solitonic excitations in a finite ensemble of ultracold bosons confined to a one-dimensional box. An optimized density-engineering potential is developed and employed together with phase imprinting to cleanly initialize gray solitons...

[Phys. Rev. A 91, 053614] Published Fri May 15, 2015

]]>We present measurements of the critical velocity for vortex shedding in a highly oblate Bose-Einstein condensate with a moving repulsive Gaussian laser beam. As a function of the barrier height ${V}_{0}$, the critical velocity ${v}_{c}$ shows a dip structure having a minimum at ${V}_{0}\approx \mu $, where $\mu $ is the chemical poten...

[Phys. Rev. A 91, 053615] Published Fri May 15, 2015

]]>Multimode waveguides can be used as multichannel devices to push the transmission bandwidth of optical signals to its limits, provided demultiplexing can be correctly performed, e.g., by selecting a given mode from the rest of the modes. This simple task is usually accomplished by Fourier filtering ...

[Phys. Rev. A 91, 053825] Published Fri May 15, 2015

]]>A unified tensor description of quadratic spin squeezing interactions is proposed, covering the single- and two-axis twisting as special cases of a general scheme. A closed set of equations of motion of the first moments and variances is derived in Gaussian approximation, and their solutions are dis...

[Phys. Rev. A 91, 053826] Published Fri May 15, 2015

]]>We address the existence and stability properties of families of gap solitons in a lower refractive-index core, sandwiched between two optical lattices with a parity-time ($\mathcal{PT}$) symmetry imprinted in a defocusing medium. The scale of flat-topped complex solitons can be controlled arbitrarily by varyin...

[Phys. Rev. A 91, 053827] Published Fri May 15, 2015

]]>We consider the nonequilibrium dynamics in quantum field theories (QFTs). After being prepared in a density matrix that is not an eigenstate of the Hamiltonian, such systems are expected to relax *locally* to a stationary state. In the presence of local conservation laws, these stationary states are b...

[Phys. Rev. A 91, 051602(R)] Published Thu May 14, 2015

]]>In open-system approaches with non-Markovian environments, the process of inserting an individual mode (denoted as “pseudomode”) into the bath or extracting it from the bath is widely employed. This procedure, however, is typically performed on basis of the spectral density and does not incorporate ...

[Phys. Rev. A 91, 052108] Published Thu May 14, 2015

]]>A simple relation is established for the evolution equation of quantum-information-processing protocols such as quantum teleportation, remote state preparation, Bell-inequality violation, and particularly the dynamics of geometric quantum correlation measures. This relation shows that when the syste...

[Phys. Rev. A 91, 052311] Published Thu May 14, 2015

]]>We present a physical (gedanken) implementation of a generalized remote state preparation of relativistic quantum field states for an arbitrary set of observers. The prepared states are created in regions that are outside the future light cone of the generating region. The mechanism, which is based ...

[Phys. Rev. A 91, 052312] Published Thu May 14, 2015

]]>Recent progress in optical lattice clocks requires unprecedented precision in controlling systematic uncertainties at the ${10}^{-18}$ level. Tuning of nonlinear light shifts is shown to reduce lattice-induced clock shift for a wide range of lattice intensity. Based on theoretical multipolar, nonlinear, an...

[Phys. Rev. A 91, 052503] Published Thu May 14, 2015

]]>The third-order susceptibility is investigated in a five-level atomic system in which the laser beams couple the ground state to a four-level closed-loop system. It is found that under the condition of the multiphoton resonance, one can enhance the Kerr nonlinearity of such a medium by properly adju...

[Phys. Rev. A 91, 053823] Published Thu May 14, 2015

]]>The laser-induced intermolecular force that exists between two or more particles in the presence of an electromagnetic field is commonly termed “optical binding.” Distinct from the single-particle forces that are at play in optical trapping at the molecular level, the phenomenon of optical binding i...

[Phys. Rev. A 91, 053824] Published Thu May 14, 2015

]]>