Physical Review A

Journal Information
ISSN / EISSN : 1050-2947 / 1094-1622
Published by: American Physical Society (APS) (10.1103)
Total articles ≅ 70,527
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Latest articles in this journal

Published: 31 December 2015
Physical Review A, Volume 92; https://doi.org/10.1103/physreva.92.062506

Abstract:
We investigate the quantum interference shifts between energetically close states, where the state structure is observed by laser spectroscopy. We report a compact and analytical expression that models the quantum interference induced shift for any admixture of circular polarization of the incident laser and angle of observation. An experimental scenario free of quantum interference can thus be predicted with this formula. Although this study is exemplified here for muonic deuterium, it can be applied to any other laser spectroscopy measurement of ns−n′p frequencies of a nonrelativistic atomic system, via an ns→n′p→n′′s scheme.
, Kevin Pack, Frank K. Wilhelm
Published: 31 December 2015
Physical Review A, Volume 92; https://doi.org/10.1103/physreva.92.063852

Abstract:
We present methods for efficient characterization of an optical coherent state |α⟩. We choose measurement settings adaptively and stochastically, based on data while it is collected. Our algorithm divides the estimation into two distinct steps: (i) before the first detection of a vacuum state, the probability of choosing a measurement setting is proportional to detecting vacuum with the setting, which makes using too similar measurement settings twice unlikely; and (ii) after the first detection of vacuum, we focus measurements in the region where vacuum is most likely to be detected. In step (i) [(ii)] the detection of vacuum (a photon) has a significantly larger effect on the shape of the posterior probability distribution of α. Compared to nonadaptive schemes, our method makes the number of measurement shots required to achieve a certain level of accuracy smaller approximately by a factor proportional to the area describing the initial uncertainty of α in phase space. While this algorithm is not directly robust against readout errors, we make it such by introducing repeated measurements in step (i).
Published: 31 December 2015
Physical Review A, Volume 92; https://doi.org/10.1103/physreva.92.062137

Abstract:
In the 1970s Smith and Tassie [G. B. Smith and L. J. Tassie, Ann. Phys. (NY) 65, 352 (1971)] and Bell and Ruegg [J. S. Bell and H. Ruegg, Nucl. Phys. B 98, 151 (1975); J. S. Bell and H. Ruegg, Nucl. Phys. B 104, 546 (1976)] independently found SU(2) symmetries of the Dirac equation with scalar and vector potentials. These symmetries, known as pseudospin and spin symmetries, have been extensively researched and applied to several physical systems. Twenty years after, in 1997, the pseudospin symmetry was revealed by Ginocchio [J. N. Ginocchio, Phys. Rev. Lett. 78, 436 (1997)] as a relativistic symmetry of the atomic nuclei when it is described by relativistic mean-field hadronic models. The main feature of these symmetries is the suppression of the spin-orbit coupling either in the upper or lower components of the Dirac spinor, thereby turning the respective second-order equations into Schrödinger-like equations, i.e, without a matrix structure. In this paper we propose a generalization of these SU(2) symmetries for potentials in the Dirac equation with several Lorentz structures, which also allow for the suppression of the matrix structure of the second-order equation of either the upper or lower components of the Dirac spinor. We derive the general properties of those potentials and list some possible candidates, which include the usual spin-pseudospin potentials, and also two- and one-dimensional potentials. An application for a particular physical system in two dimensions, electrons in graphene, is suggested.
João P. Amaral, Eduardo J. S. Fonseca,
Published: 31 December 2015
Physical Review A, Volume 92; https://doi.org/10.1103/physreva.92.063851

Abstract:
We use a phase-only computer-generated hologram to encode both phase and amplitude of a power of Rayleigh speckles. This method allows us to generate speckles with enhanced and reduced contrast without any optimization process. We explore non-Rayleigh speckles and unveil, theoretically and experimentally, their first-order statistical properties. These speckles may find applications in syntheses of disordered optical potentials for cold atoms and colloidal particles, in speckle illumination imaging, and in wave interference studied through spatial intensity correlation.
Sayan Choudhury,
Published: 31 December 2015
Physical Review A, Volume 92; https://doi.org/10.1103/physreva.92.063639

Abstract:
We explore the effect of transverse confinement on the stability of a Bose-Einstein condensate loaded in a shaken one-dimensional or two-dimensional square lattice. We calculate the decay rate from two-particle collisions. We predict that if the transverse confinement exceeds a critical value, then, for appropriate shaking frequencies, the condensate is stable against scattering into transverse directions. We explore the confinement dependence of the loss rate, explaining the rich structure in terms of resonances.
Phay J. Ho, E. P. Kanter, L. Young
Published: 31 December 2015
Physical Review A, Volume 92; https://doi.org/10.1103/physreva.92.063430

Abstract:
We describe the methodology of our recently developed Monte Carlo rate equation (MCRE) approach, which systematically incorporates bound-bound resonances to model multiphoton ionization dynamics induced by high-fluence, high-intensity x-ray free-electron laser (XFEL) pulses. These resonances are responsible for ionization far beyond that predicted by the sequential single photon absorption model and are central to a quantitative understanding of atomic ionization dynamics in XFEL pulses. We also present calculated multiphoton ionization dynamics for Kr and Xe atoms in XFEL pulses for a variety of conditions, to compare the effects of bandwidth, pulse duration, pulse fluence, and photon energy. This comprehensive computational investigation reveals areas in the photon energy–pulse fluence landscape where resonances are critically important. We also uncover a mechanism, preservation of inner-shell vacancies (PIVS), whereby radiation damage is enhanced at higher XFEL intensities and identify the sequence of core-outer–Rydberg, core-valence, and core-core resonances encountered during multiphoton x-ray ionization.
Published: 30 December 2015
Physical Review A, Volume 92; https://doi.org/10.1103/physreva.92.062133

Abstract:
The use of weak measurements for performing quantum tomography is enjoying increased attention due to several recent proposals. The claimed merits of using weak measurements in this context are varied, but are generally represented by novelty, increased efficacy, and foundational significance. We critically evaluate two proposals that make such claims and find that weak measurements are not an essential ingredient for most of their claimed features.
Xue-Na Zhu, Shao-Ming Fei
Published: 30 December 2015
Physical Review A, Volume 92; https://doi.org/10.1103/physreva.92.062345

Abstract:
We present a different kind of monogamous relations based on concurrence and concurrence of assistance. For N-qubit systems ABC1...CN−2, the monogamy relations satisfied by the concurrence of N-qubit pure states under the partition AB and C1...CN−2, as well as under the partition ABC1 and C2...CN−2, are established, which gives rise to a kind of restrictions on the entanglement distribution and trade off among the subsystems.
Published: 30 December 2015
Physical Review A, Volume 92; https://doi.org/10.1103/physreva.92.062134

Abstract:
We present Bell-type tests of nonclassicality and non-Gaussianity for single-mode fields employing a generalized quasiprobability function. Our nonclassicality tests are based on the observation that two orthogonal quadratures in phase space (position and momentum) behave as independent realistic variables for a coherent state. Taking four (three) points at the vertices of a rectangle (right triangle) in phase space, our tests detect every pure nonclassical Gaussian state and a range of mixed Gaussian states. These tests also set an upper bound for all Gaussian states and their mixtures, which thereby provide criteria for genuine quantum non-Gaussianity. We optimize the non-Gaussianity tests by employing a squeezing transformation in phase space that converts a rectangle (right triangle) to a parallelogram (triangle), which enlarges the set of non-Gaussian states detectable in our formulation. We address fundamental and practical limits of our generalized phase-space tests by looking into their relation with decoherence under a lossy Gaussian channel and their robustness against finite data and nonoptimal choice of phase-space points. Furthermore, we demonstrate that our parallelogram test can identify useful resources for nonlocality testing in phase space.
Shaoqi Zhu,
Published: 30 December 2015
Physical Review A, Volume 92; https://doi.org/10.1103/physreva.92.063637

Abstract:
We have numerically calculated the single-band Wannier functions for interacting Bose gases in optical lattices with a self-consistent approach. We find that the Wannier functions are broadened by repulsive interaction. The tunneling parameter J and the on-site interaction U computed with the broadened Wannier functions are found to change significantly with the number of atoms per site. Our theory can explain the nonuniform atomic clock shift observed in Campbell et al., Science 313, 649 (2006).
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