The limaçon-shaped semiconductor microcavity is a ray-chaotic cavity sustaining low-loss modes with mostly unidirectional emission patterns. Investigating these modes systematically, we show that the modes correspond to ray description collectively rather than individually. In addition, we present experimental data on multimode lasing emission patterns that show high unidirectionality and closely agree with the ray description. The origin of this agreement is well explained by the collective correspondence mechanism.

In this paper, employing the Itô stochastic Schrödinger equation, we extend Bell’s beable interpretation of quantum mechanics to encompass dissipation, decoherence, and the quantum-to-classical transition through quantum trajectories. For a particular choice of the source of stochasticity, the one leading to a dissipative Lindblad-type correction to the Hamiltonian dynamics, we find that the diffusive terms in Nelsons stochastic trajectories are naturally incorporated into Bohm’s causal dynamics, yielding a unified Bohm-Nelson theory. In particular, by analyzing the interference between quantum trajectories, we clearly identify the decoherence time, as estimated from the quantum formalism. We also observe the quantum-to-classical transition in the convergence of the infinite ensemble of quantum trajectories to their classical counterparts. Finally, we show that our extended beables circumvent the problems in Bohm’s causal dynamics regarding stationary states in quantum mechanics.

We exactly diagonalize the finite-size $XY$ model with periodic boundary conditions and analytically determine the ground-state energy. We show that there are two types of Bogoliubov fermions, singles and pairs, whose dispersion relations have a completely arbitrary gauge-dependent sign. It follows that the ground state can be determined by a competition between the vacuum states (with a suitable gauge) of two parity sectors. We finally exhibit some points in finite-size systems that forerun criticality. They are associated to single Bogoliubov fermions and to the level crossings between physical and unphysical states. In the thermodynamic limit, they approach the ground state and build up singularities at logarithmic rates.

Based on the standard criteria [P. van Loock and A. Furusawa, Phys. Rev. A 67, 052315 (2003)], we propose a scheme to achieve the fully tripartite continuous-variable (CV) entanglement in a $Y$-type atomic system driven by two strong classical fields. By numerically simulating the dynamics of system, we show that the generation of entanglement does not depend intensively on the initial condition of cavity field and the time for which the cavity modes remain entangled can be prolonged via enhancing the intensities of classical fields in our scheme. Moreover, our numerical results also show that a tripartite entanglement amplifier can be realized in the present scheme. The present research provides an efficient approach to achieve fully tripartite CV entangled state even when the three entangled modes have different frequencies and initial states, which may be useful for the progress of quantum information networks with many nodes.

We propose a quantum cloning machine, which clones a qubit into two clones assuming known modulus of expectation value of Pauli ${\sigma }_z$ matrix. The process is referred to as the mirror phase-covariant cloning for which the input state is a priori less known than that for the standard phase-covariant cloning. Analytical expressions describing the cloning transformation and fidelity of the clones are found. Extremal equations for the optimal cloning are derived and analytically solved by generalizing a method of Fiurášek [Phys. Rev. A 64, 062310 (2001)]. Quantum circuits implementing the optimal cloning transformation and their physical realization in a quantum-dot system are described.

Absolute cross sections for the projectile single-electron loss and single- and double-electron capture of ${\text{B}}^{2+}$ ions colliding with Ne and Ar targets and ${\text{C}}^{3+}$ ions colliding with Ar targets, in the energy range from 0.1 to 4.0 MeV, have been measured. Cross sections for the single capture channel have been calculated using the classical Bohr-Lindhard model, showing good agreement with the experiment. In the single electron-loss process, calculations were performed using both an extended version of the classical-impulse free-collision model and the plane-wave Born approximation (PWBA) for the screening mechanism, added to antiscreening cross sections calculated with the PWBA, thus providing total single electron-loss cross sections. The total cross sections obtained from the former method provided very good descriptions of the single electron-loss measured data, much better than those from the PWBA. The antiscreening calculations have been compared to experimental cross sections for ionization of ${\text{B}}^{2+}$ and ${\text{C}}^{3+}$ ions by electrons, within the independent-particle model, showing a good agreement in the asymptotic high-velocity region.

Calculations relating to two experiments that demonstrate coherent control of preformed rubidium-85 molecules in a magneto-optical trap using ultrafast laser pulses are presented. The two experiments are a step toward the stabilization of ultracold rubidium dimers using ultrafast lasers. In the first experiment, it is shown that preassociated molecules in an incoherent mixture of states can be made to oscillate coherently using a single ultrafast pulse. A mechanism that can transfer molecular population to more deeply bound vibrational levels is used in the second. Optimal parameters of the control pulse are presented for the application of the mechanism to molecules in a magneto-optical trap. The calculations make use of an experimental determination of the initial state of molecules photoassociated by the trapping lasers in the magneto-optical trap and use shaped pulses consistent with a standard ultrafast laser system. The experiment’s purpose is to demonstrate and evaluate the use of ultrafast shaped pulses to manipulate ultracold rubidium dimers with a view to the eventual stabilization of the molecules.

An experimental pump-probe study of the photoassociative creation of translationally ultracold rubidium molecules is presented together with numerical simulations of the process. The formation of loosely bound excited-state dimers is observed as a first step toward a fully coherent pump-dump approach to the stabilization of ${\text{Rb}}_2$ into its lowest ground vibrational states. The population that contributes to the pump-probe process is characterized and found to be distinct from a background population of preassociated molecules.

The angular dependence of high-order harmonic generation (HHG) from molecules lacking inversion symmetry (MLIS) is investigated using polarization gating method. The polarization gating with 5 fs, 750 nm laser pulses is an effective way to confine the recollision of electron wave packet within one half cycle. It is shown that the dramatic changes of HHG yields are observed when the MLISs are rotated by $180°$. This feature implies that HHG can be manipulated by MLIS themselves. Moreover, polarization gating with 10 fs pulses are applicable for generating supercontinuous high harmonics from MLIS. Note that the pulse duration we used is twice as long as that for applying polarization gating method to atoms.

We explore the high-density, nonlinear regime of atom-cavity coupling for a gas of three-level atoms at high temperature inside an optical cavity, interacting with the cavity field and a strong driving field. We find a region of parameters where the two side peaks in the transmission spectrum (which, in the linear regime, are associated with “bright polaritons”) split into two pairs of peaks. Experimental results are presented along with a theoretical model that indicates that this phenomenon is unique to the three-level system in the large Doppler-broadening regime.

We study how an optical parametric amplifier inside the cavity can affect the normal-mode splitting behavior of the coupled movable mirror and the cavity field. We work in the resolved sideband regime. The spectra exhibit a double-peak structure as the parametric gain is increased. Moreover, for a fixed parametric gain, the double-peak structure of the spectrum is more pronounced with increasing the input laser power. We give results for mode splitting. The widths of the split lines are sensitive to parametric gain.

Based on the Ginzburg-Landau framework, we find that $p$-wave superfluids of neutral atom gases in three-dimensional harmonic traps exhibit spontaneous mass current at rest with direction dependent on trap geometry. Under rotation, various types of order parameter textures are stabilized including Mermin-Ho and Anderson-Toulouse-Chechetkin vortices. In a cigar shape trap, spontaneous current flows parallel to the rotation axis and thus perpendicular to the ordinary rotational current. The spontaneous mass current at rest and texture formation can be used to investigate $p$-wave superfluidity.

We create atom-molecule superpositions in a Bose-Fermi mixture of ${}^{87}\text{R}\text{b}$ and ${}^{40}\text{K}$ atoms. The superpositions are generated by ramping an applied magnetic field near an interspecies Fano-Feshbach resonance to coherently couple atom and molecule states. Rabi- and Ramsey-type experiments show oscillations in the molecule population that persist as long as $150\mu \text{s}$ and have up to 50% contrast. The frequencies of these oscillations are magnetic-field dependent and consistent with the predicted molecule binding energy. This quantum superposition involves a molecule and a pair of free particles with different statistics (i.e., bosons and fermions) and furthers exploration of atom-molecule coherence in systems without a Bose-Einstein condensate.

We compute concurrence and negativity as measures of two-spin entanglement generated by a power-law quench (characterized by a rate ${\tau }^{-1}$ and an exponent $\alpha$) which takes an anisotropic $XY$ chain in a transverse field through a quantum critical point (QCP). We show that only spins separated by an even number of lattice spacings get entangled in such a process. Moreover, there is a critical rate of quench, ${\tau }_c^{-1}$, above which no two-spin entanglement is generated; the entire entanglement is multipartite. The ratio of the entanglements between consecutive even neighbors can be tuned by changing the quench rate. We also show that for large $\tau$, the concurrence (negativity) scales as $\sqrt{\alpha /\tau }$ $\left(\alpha /\tau \right)$, and we relate this scaling behavior to defect production by the quench through a QCP.

The scaled static dipole polarizabilities of $1s$ and $2s$ states of hydrogenlike ions embedded in a plasma environment are calculated as function of the interaction screening. The plasma screening of Coulomb interaction is described by the Debye-Hückel potential. The electron energies and wave functions of bound and continuum states are calculated by solving numerically the Schrödinger equation with this potential in a symplectic integration scheme. The screening of Coulomb interactions reduces the number of bound states, decreases the energies of bound states and broadens the radial extension of the wave functions of bound and continuum states. All these effects result in a dramatic increase in static polarizability when the interaction screening increases. Comparison of present results with those of other authors is made when available.

Cross sections have been determined for electron transfer, direct excitation, and ionization in collisions between protons and $\text{H}\left(1s\right)$ atoms at proton energies from 1 keV to 16 MeV, extending the pioneering work by Shakeshaft [R. Shakeshaft, Phys. Rev. A 14, 1626 (1976); Phys. Rev. A 18, 1930 (1978)] with a much smaller basis and energy range, and following the author’s work for other collisional systems [T. G. Winter, Phys. Rev. A 76, 062702 (2007)]. Transfer as well as excitation cross sections into individual states up to $3d$ (excitation up to $4f$ at the higher energies) have been determined with several coupled-Sturmian-pseudostate bases, and tests of basis sensitivity have been carried out. These and ionization cross sections have been compared with experimental, other coupled-state, and numerical results. Ionization and excitation cross sections have also been compared with corresponding Born results at higher energies.

This paper revisits positron scattering from molecular hydrogen, in an attempt to provide accurate total cross-section data against which theoretical calculations might be benchmarked. The present data were measured over the energy range 0.1–50 eV and, where possible, are compared to results from previous experiments and calculations. Agreement with the earlier data was typically very good at energies above 10 eV but becomes progressively more marginal as we go to lower energies. None of the current theories quantitatively reproduce our measurements over the entire energy range, although at a qualitative level the main features driving the scattering dynamics are apparent.

Two atoms in an optical lattice may be made to interact strongly at higher partial waves near a Feshbach resonance. These atoms, under appropriate constraints, could be bosonic or fermionic. The universal $l=2$ energy spectrum for such a system, with a caveat, is presented in this paper and checked with the spectrum obtained by direct numerical integration of the Schrödinger equation. The results reported here extend those of Yip for $p$-wave resonance [S.-K. Yip, Phys. Rev. A 78, 013612 (2008)], while exploring the limitations of a universal expression for the spectrum for the higher partial waves.

We study the use of squeezed light for qubit coherent control and compare it with the coherent-state control field case. We calculate the entanglement between a short pulse of resonant squeezed light and a two-level atom in free space and the resulting operation error. We find that the squeezing phase, the phase of the light field, and the atomic superposition phase all determine whether atom-pulse mode entanglement and the gate error are enhanced or suppressed. When averaged over all possible qubit initial states, the gate error would not decrease by a practically useful amount and would in fact increase in most cases. However, the enhanced entanglement may be of use in quantum communication schemes. We discuss the possibility of measuring the increased gate error as a signature of the enhancement of entanglement by squeezing.

We present a three-dimensional theory of stimulated Raman scattering (SRS) or super-radiance. In particular we address how the spatial and temporal properties of the generated SRS beam or Stokes beam of radiation depends on the spatial properties of the gain medium. Maxwell equations for the Stokes field operators and of the atomic operators are solved analytically and a correlation function for the Stokes field is derived. In the analysis we identify a super-radiating part of the Stokes radiation that exhibit beam characteristics. We show how the intensity in this beam builds up in time and at some point largely dominates the total Stokes radiation of the gain medium. We show how the SRS depends on the Fresnel number and the optical depth and that in fact these two factors are the only factors describing the coherent radiation.