The dynamics of a simple spin chain (two spins) coupled to bosonic baths at different temperatures is studied. The analytical solution for the reduced density matrix of the system is found. The dynamics and temperature dependence of spin-spin entanglement is analyzed. It is shown that the system converges to a steady state. If the energy levels of the two spins are different, the steady-state concurrence assumes its maximum at unequal bath temperatures. It is found that a difference in local energy levels can make the steady-state entanglement more stable against high temperatures.

The linear combination of atomic orbitals approach to the calculation of the molecular continuum spectrum with $B$-spline basis functions has been applied to the calculation of the first-order nondipolar corrections to the photoelectron angular distributions from carbon tetrafluoride. Dipolar and nondipolar asymmetry parameter profiles have been calculated for every single-particle orbital ionization. A comparison with the available experimental data gives good agreement for the dipolar asymmetry parameter. Nondipolar asymmetry parameters are affected by the presence of resonant processes in the dipolar channels. In the absence of experimental data, the good agreement of the computed dipolar parameters with experimental data makes one confident of the predictive quality of the theoretical results.

Single-photon double ionization of He, ${\mathrm{Li}}^{+}$, ${\mathrm{Be}}^{2+}$, and ${\mathrm{H}}^{-}$, as well as the $K$ shell of neutral Li and Be atoms with “hollow ion” formation, is studied using the ab initio time-dependent scaling method that has an advantage of avoiding the explicit use of double continuum correlated functions and allows one to obtain complete information about the threefold differential cross section in a large range of the incident photon energies in a single calculation. It is shown that the dependence of the Gaussian width parameter, that characterizes the angular distribution of threefold differential cross section, on the photon energy exhibits an approximate charge scaling law for angular distribution. The energy values, at which the angular distributions for different targets are similar to those of helium atom, are found. An intriguing violation of Wannier threshold law for hydrogen negative ion is observed.

We present a quantum-mechanical treatment of the mechanical stirring of Bose-Einstein condensates using classical field techniques. In our approach the condensate and excited modes are described using a Hamiltonian classical field method in which the atom number and (rotating frame) energy are strictly conserved. We simulate a $T=0$ quasi-two-dimensional condensate perturbed by a rotating anisotropic trapping potential. Vacuum fluctuations in the initial state provide an irreducible mechanism for breaking the initial symmetries of the condensate and seeding the subsequent dynamical instability. Highly turbulent motion develops and we quantify the emergence of a rotating thermal component that provides the dissipation necessary for the nucleation and motional damping of vortices in the condensate. Vortex lattice formation is not observed, rather the vortices assemble into a spatially disordered vortex liquid state. We discuss methods we have developed to identify the condensate in the presence of an irregular distribution of vortices, determine the thermodynamic parameters of the thermal component, and extract damping rates from the classical field trajectories.

Thermodynamic properties of an ultracold Fermi gas in a harmonic trap are calculated within a local density approximation, using a conserving many-body formalism for the BCS to Bose-Einstein condensate crossover problem, which has been developed by Haussmann et al. [Phys. Rev. A 75, 023610 (2007)]. We focus on the unitary regime near a Feshbach resonance and determine the local density and entropy profiles and the global entropy $S\left(E\right)$ as a function of the total energy $E$. Our results are in good agreement with both experimental data and previous analytical and numerical results for the thermodynamics of the unitary Fermi gas. The value of the Bertsch parameter at $T=0$ and the superfluid transition temperature, however, differ appreciably. We show that, well in the superfluid regime, removal of atoms near the cloud edge enables cooling far below temperatures that have been reached so far.

We discuss the effect of an adiabatic rotation on the phase separation between the superfluid and normal component of a trapped polarized Fermi gas at unitarity and zero temperature, under the assumption that quantized vortices are not formed. We show that the Chandrasekhar-Clogston limit $n_{\downarrow }∕n_{\uparrow }$ characterizing the local polarization in the normal phase at the interface is enhanced by the rotation as a consequence of the centrifugal effect. The density profiles (local and column integral) of the two spin species are calculated as a function of the angular velocity for different values of the polarization. The critical value of the angular velocity at which the superfluid exhibits a spontaneous quadrupole deformation is also calculated for the unpolarized case.

The dynamics of a system composed of two coupled cavities, each containing a single two-level atom, is studied over a wide range of detuning and coupling values. A description of the field in terms of delocalized modes reveals that the detuning between the atoms and these modes is controlled by the coupling between the cavities; this detuning in turn governs the nature of the dynamics. If the atoms are highly detuned from both delocalized field modes, the dynamics become dispersive and an excitation may be transferred from the first atom to the second without populating the field. In the case of resonance between the atoms and one of the delocalized modes, state transfer between the atoms requires intermediate excitation of the field. Thus, the interaction between the two atoms can be controlled by adjusting the coupling between the cavities.

We provide a detailed analysis of the three-dimensional spatial coherence properties of light speckles, based on very general assumptions. We show that, while in the deep Fresnel region close to the source the longitudinal coherence of speckles is ruled by the laws of ordinary diffraction, on approach to the Fraunhofer zone the longitudinal coherence length tends to become infinite. We offer both a quantitative and a qualitative description of the emergence of these different behaviors.

Adiabatically shape-preserving-wave and solitary-wave solutions for five-level atomic systems are presented. They give the idealized situations for the shape preserving propagation of optical waves through a five-level atomic medium, and provide some useful comparisons with the electromagnetically induced transparency experiments performed by Harris and his collaborators on atoms with hyperfine structure.

Gas-phase multiply charged proteins have been sympathetically cooled to translational temperatures below $1\mathrm{K}$ by Coulomb interaction with laser-cooled barium ions in a linear ion trap. In one case, an ensemble of 53 cytochrome c molecules (mass $\simeq 12390\mathrm{amu}$, charge $+17e$) was cooled by $\simeq 160$ laser-cooled barium ions to less than $0.75\mathrm{K}$. Storage times of more than $20\min$ have been observed and could easily be extended to more than an hour. The technique is applicable to a wide variety of complex molecules.

The ${}^4\mathrm{He}_3$ system is studied using the adiabatic hyperspherical representation. We adopt the current state-of-the-art helium interaction potential including retardation and the nonadditive three-body term to calculate all low-energy properties of the triatomic ${}^4\mathrm{He}$ system. The bound state energies of the ${}^4\mathrm{He}$ trimer are computed as well as the ${}^4\mathrm{He}+{}^4\mathrm{He}_2$ elastic scattering cross sections, the three-body recombination, and collision induced dissociation rates at finite temperatures. We also treat the system that consists of two ${}^4\mathrm{He}$ and one ${}^3\mathrm{He}$ atoms, and compute the spectrum of the isotopic trimer ${}^4\mathrm{He}_2{}^3\mathrm{He}$, the ${}^3\mathrm{He}+{}^4\mathrm{He}_2$ elastic scattering cross sections, the rates for three-body recombination, and the collision induced dissociation rate at finite temperatures. The effects of retardation and the nonadditive three-body term are investigated. Retardation is found to be significant in some cases, while the three-body term plays only a minor role for these systems.

We consider the atom-optical $\delta$-kicked accelerator when the initial momentum distribution is symmetric. We demonstrate the existence of quantum-resonant dynamics, and derive analytic expressions for the system evolution. In particular, we consider the dynamical evolution of the momentum moments and find that all even-ordered momentum moments exhibit a power-law growth. In the ultracold (zero-temperature) limit the exponent is determined by the order of the moment, whereas for a broad, thermal initial momentum distribution the exponent is reduced by 1. To demonstrate the power-law behavior explicitly we consider the evolutions of the second- and fourth-order momentum moments, and cumulants, for an initially Gaussian momentum distribution corresponding to the Maxwell-Boltzmann distribution of an ideal gas at thermal equilibrium.

We experimentally demonstrate the nonclassical photon number correlations expected in tripartite continuous-variable states obtained by parametric processes. Our scheme involves a single nonlinear crystal, where two interlinked parametric interactions take place simultaneously, and represents a bright and compact source of a sub-shot-noise tripartite light field. We analyze the effects of the pump intensities on the numbers of detected photons and on the amount of noise reduction in some detail, thus demonstrating a good agreement between the experimental data and a single-mode theoretical description.

The intensities of the circulating pulses in a mode-locked ring laser are shown to be analogous to the population transfer (Rabi cycle) in a two-level system. We present an experimental demonstration of this analogy.

We study the radiative decay of a cesium atom near a nanofiber in the presence of a weak magnetic field. We show that the direction of the magnetic field relative to the fiber axis plays an important role in deciding the radiative decay from the atom. We find that the decay rates for the different magnetic sublevels of the atom are spread in a wider range in the orthogonal configuration than those in the coaxial configuration. We also show that the cross decay coefficients depend substantially on the orientation of the magnetic field relative to the fiber axis.

Optical field fluctuations in self-defocusing media can be described in terms of sound waves in a two-dimensional photon fluid. It is shown that, while the background fluid couples with the usual flat metric, soundlike waves experience an effective curved spacetime determined by the physical properties of the flow. In an optical cavity configuration, the background spacetime can be suitably controlled by the driving beam, allowing the formation of acoustic ergoregions and event horizons. An experiment simulating the main features of the rotating black hole geometry is proposed.

We investigate the disentanglement dynamics of generalized multiqubit Greenberger-Horne-Zeilinger-type states $\mid {\Psi }_{n,N}⟩=\alpha {\mid 1⟩}^{\otimes n}{\mid 0⟩}^{\otimes (N-n)}+\beta {\mid 0⟩}^{\otimes n}{\mid 1⟩}^{\otimes (N-n)}$ (with $1⩽n<N$) in a local decoherence environment. By adopting the time after which all the bipartite entanglements vanish or become negligibly small as the criterion of entanglement robustness, we show that states $\mid {\Psi }_{n,N}⟩$ are more robust than states $\mid {\Psi }_N⟩=\alpha {\mid 0⟩}^{\otimes N}+\beta {\mid 1⟩}^{\otimes N}$ in all respects. Since the two states $\mid {\Psi }_N⟩$ and $\mid {\Psi }_{n,N}⟩$ can be transformed into each other by local operations, we confirm that entanglement robustness can be enhanced by local operations though the amount of entanglement cannot.

We describe a continuous-variable scheme for simulating the Kitaev lattice model and for detecting statistics of Abelian anyons. The corresponding quantum optical implementation is solely based upon Gaussian resource states and Gaussian operations, hence allowing for a highly efficient creation, manipulation, and detection of anyons. This approach extends our understanding of the control and application of anyons and it leads to the possibility for experimental proof-of-principle demonstrations of anyonic statistics using continuous-variable systems.

Optimal generalized measurements for state estimation are well understood. However, practical quantum state tomography is typically performed using a fixed set of projective measurements, and the question of how to choose these measurements has been largely unexplored in the literature. In this work, we develop theoretical asymptotic bounds for the average fidelity of pure qubit tomography using measurement sets whose axes correspond to faces of Platonic solids. We also present comprehensive simulations of maximum likelihood tomography for mixed qubit states using the Platonic solid measurements. We show that overcomplete measurement sets can be used to improve the accuracy of tomographic reconstructions.

The optimal $N$ qubit states featuring highest sensitivity to small misalignment of Cartesian reference frames are found using the quantum Cramér-Rao bound. It is shown that the optimal states are supported on the symmetric subspace and hence are mathematically equivalent to a single spin $J=N∕2$. Majorana representation of spin states is used to reveal a beautiful connection between the states optimal for aligning reference frames and the platonic solids.