We investigate the existence and stability of various types of spatial solitons in a three-level atomic medium with Laguerre-Gaussian control beam. Radial and azimuthal modulations of the medium properties, introduced by the control beam, provide possibilities for existence of diverse soliton patterns and dynamics. Beam diffraction provides additional soliton controllability. All types of solitons can be generated at very low input energy at a few-photon level.

We investigate the properties of time reversibility of a soliton gas, originating from a dispersive regularization of a shock wave, as it propagates in a strongly disordered environment. An original approach combining information measures and spin glass theory shows that time-reversal focusing occurs for different replicas of the disorder in forward and backward propagation, provided the disorder varies on a length scale much shorter than the width of the soliton constituents. The analysis is performed by starting from a new class of reflectionless potentials, which describe the most general form of an expanding soliton gas of the defocusing nonlinear Schrödinger equation.

We propose a scheme to realize a transition from delocalization to localization of light waves via electromagnetically induced transparency. The system we suggested is a resonant cold atomic ensemble having $N$ configuration, with a control field consisting of two pairs of laser beams with different cross angles, which produce an electromagnetically induced quasiperiodic waveguide (EIQPW) for the propagation of a signal field. By appropriately tuning the incommensurate rate or relative modulation strength between the two pairs of control-field components, the signal field can exhibit the delocalization-localization transition as it transports inside the atomic ensemble. The delocalization-localization transition point is determined and the propagation property of the signal field is studied in detail. Our work provides a way of realizing wave localization via atomic coherence, which is quite different from the conventional, off-resonant mechanism-based Aubry-Andre model, and the great controllability of the EIQPW also allows an easy manipulation of the delocalization-localization transition.

We analyze theoretically a scheme that produces spin squeezing via the continuous swapping of atom-photon entanglement into atom-atom entanglement, and propose an explicit experimental system where the necessary atom-field coupling can be realized. This scheme is found to be robust against perturbations due to other atom-field coupling channels.

Off-resonant Raman interaction of a single-photon wave packet and a classical control field in an atomic medium with controlled refractive index is investigated. It is shown that a continuous change of refractive index during the interaction leads to the mapping of a single photon state to a superposition of atomic collective excitations (spin waves) with different wave vectors and vice versa. The suitability of refractive-index control for developing multichannel quantum memories is discussed and possible schemes of implementation are considered.

We report on a combined experimental and theoretical study of polarization self-rotation in an ultracold atomic sample. In the experiments, a probe laser is tuned in the spectral vicinity of the $D_1$ line to observe polarization self-rotation in a sample of ultracold ${}^{87}\mathrm{Rb}$ prepared in a magneto-optical trap (MOT). Systematic measurements of the rotation angle of the light-polarization ellipse as a function of laser intensity, initial ellipticity, and detuning are made. The observations, in good agreement with theoretical simulations, are indicative of the presence of a residual static magnetic field, resulting in measured asymmetries in the rotation angle for right and left ellipticities. In this paper we present our detailed experimental results and analysis of the combined influences of polarization self-rotation and the Faraday effect.

We propose a scheme for parallel, spatially multimode quantum memory for light. The scheme is based on the propagation in different directions of a quantum signal wave and strong classical reference wave, like in a classical volume hologram and the previously proposed quantum volume hologram [D. V. Vasilyev et al., Phys. Rev. A 81, 020302(R) (2010)]. The medium for the hologram consists of a spatially extended ensemble of cold spin-polarized atoms. In the absence of the collective spin rotation during the interaction, two passes of light for both storage and retrieval are required, and therefore the present scheme can be called a double-pass quantum volume hologram. The scheme is less sensitive to diffraction and therefore is capable of achieving a higher density of storage of spatial modes as compared to the previously proposed thin quantum hologram [D. V. Vasilyev et al., Phys. Rev. A 77, 020302(R) (2008)], which also requires two passes of light for both storage and retrieval. However, the present scheme allows one to achieve a good memory performance with a lower optical depth of the atomic sample as compared to the quantum volume hologram. A quantum hologram capable of storing entangled images can become an important ingredient in quantum information processing and quantum imaging.

The enhanced collective coupling to weak quantum fields may turn atomic or spin ensembles into an important component in quantum information processing architectures. Inhomogeneous broadening can, however, significantly reduce the coupling and the lifetime of the collective excitation that represent the quantum information. In this paper we show that the width and shape of the inhomogeneous broadening have a striking influence on the dynamics of the cavity-ensemble system and may lead to narrowing of the linewidth of the collective states. We underpin our findings with the examples of a Gaussian and a Lorentzian profile of the inhomogeneity.

Recent experiments have demonstrated how quantum-mechanical impurities can be created within strongly correlated quantum gases and used to probe the coherence properties of these systems [S. Palzer, C. Zipkes, C. Sias, and M. Köhl, Phys. Rev. Lett. 103, 150601 (2009).]. Here we present a phenomenological model to simulate such an output coupler for a Tonks-Girardeau gas that shows qualitative agreement with the experimental results for atom transport and output coupling. Our model allows us to explore nonequilibrium transport phenomena in ultracold quantum gases and leads us to predict a regime of atom blockade, where the impurity component becomes localized in the parent cloud despite the presence of gravity. We show that this provides a stable mixed-species quantum gas in the strongly correlated limit.

The ground-state properties of neutral hard-core bosons trapped in an optical two-leg ladder in the presence of an artificial magnetic field are studied. For a weak field, two separated peaks appear in the momentum distribution as a signature of the Meissner state in which bosons, carrying persistent currents on each leg, condense into finite-momentum states, while for a strong field, a central peak and tiny bumps associated with the vortex lattice structure indicate that the ground state is the vortex state.

We show that dressing polar molecules with a far-off-resonant optical field leads to new types of intermolecular potentials, which undergo a crossover from the inverse power to oscillating behavior depending on the intermolecular distance, and whose parameters can be tuned by varying the laser intensity and wavelength. We present analytic expressions for the potential energy surfaces, thereby providing direct access to the parameters of an optical field required to design intermolecular interactions experimentally.

In a recent paper we have studied the peculiar features of the Berry and Aharonov-Anandan geometric phases for isolated spins $S⩾1.$ We have assumed that they are submitted to a dipole and quadrupole coupling to external $\mathbf{E}$ and $\mathbf{B}$ fields with the mild restriction $\mathbf{E}·\mathbf{B}=0$. This implies discrete symmetries leading to remarkable simplifications of the geometry and algebra involved. The aim of the present work is to describe realistic proposals, within the realm of atomic physics, for the verification of some of our most significant theoretical predictions. There are several challenges to be overcome. For alkali-metal atoms, most commonly used in atomic interferometers, the only practical way to generate quadrupole coupling, with a strength comparable to the dipole one, is the ac Stark effect induced by a nearly resonant light beam. One then has to face the instability of the“dressed” atom hyperfine (hf) level, a candidate for our isolated spin. One deleterious effect is the apparition of an imaginary part in the quadrupole to dipole coupling strength ratio, $\lambda$. Fortunately we have found a simple way to get rid of $\mathfrak{I}(\lambda )$ by an appropriate detuning. We are left with an unstable isolated spin. This implies an upper bound to the quantum cycle duration $T_c$. In the case of the Berry’s phase, $T_c$ has a lower bound due to the necessity of keeping the nonadiabatic corrections below a predefined level. We have found a compromise in the case of the $F=2,m=0$ ${}^{87}\mathrm{Rb}$ ground-state hf level. This is our candidate for the measurement of the somewhat “exotic” Berry’s phase acquired by the $S=2,m=0$ state at the end of a quantum cycle involving a rotation of $\pi$ of the $\mathbf{E}$ field—in practice, the linear polarization of the dressing beam —about the $\mathbf{B}$ field direction. We have found a way to implement, in a Ramsey-type interferometric measurement, the procedures aimed at controlling the nonadiabatic corrections, as described in detail in our previous theoretical paper. A numerical simulation of our experimental proposal shows that a $0.1\%$ accurate determination of Berry’s phase, free of nonadiabatic corrections, can be achieved. Measurements could also be considered for cold ${}^{52}\mathrm{Cr}$ chromium atoms with $S=3$, where values of $\lambda \simeq 1$ can be obtained with an instability smaller than in the ${}^{87}\mathrm{Rb}$ case, due to a more favorable spectroscopic structure. The $F=1,m=1$ hf level of the ${}^{87}\mathrm{Rb}$ ground state offers the opportunity to extend the measurement of Aharonov-Anandan’s phases beyond the case $S=\frac{1}{2}$. We construct, using “light shift,” the Hamiltonian $H_{\parallel }(t)$ generating a closed circuit in the density-matrix space which satisfies at any time the “parallel transport” condition, thus making the quantum cycle free from the adiabaticity condition. We also consider the case of half-integer spins (e.g., ${}^{201}\mathrm{Hg}$, ${}^{135}\mathrm{Ba}$, and ${}^{137}\mathrm{Ba}$), with their own specific features. We show how the difference of Berry’s phases for states $S=\frac{3}{2}$ and $S=\frac{1}{2}$, with $m=\frac{1}{2}$, can be exploited to achieve a holonomic maximum entanglement of three qubits.

We investigate continuous-variable (CV) multipartite unlockable bound entangled states. Comparing with the qubit multipartite unlockable bound entangled states, CV multipartite unlockable bound entangled states present some new and different properties. CV multipartite unlockable bound entangled states may serve as a useful quantum resource for new multiparty communication schemes. The experimental protocol for generating CV unlockable bound entangled states is proposed with a setup that is, at present, accessible.

In the change point problem, we determine when the observed distribution has changed to another one. We expand this problem to a quantum case where copies of an unknown pure state are being distributed. That is, we estimate when the distributed quantum pure state is changed. As the most fundamental case, we treat the problem of deciding the true change point $t_c$ between the two given candidates $t_1$ and $t_2$. Our problem is mathematically equal to identifying a given state with one of the two unknown states when multiple copies of the states are provided. The minimum of the averaged error probability is given and the optimal positive operator-valued measure (POVM) is given to obtain it when the initial and final quantum pure states are subject to the invariant prior. We also compute the error probability for deciding the change point under the above POVM when the initial and final quantum pure states are fixed. These analytical results allow us to calculate the value in the asymptotic case.

A comprehensive study of the $X\hspace{0.5em}{}^1\Sigma {}^{+}$ and $a\hspace{0.5em}{}^3\Sigma {}^{+}$ electronic states of the Rb and Cs atom pair in RbCs is presented. Abundant spectroscopic data for the ${}^{85}\mathrm{Rb}$${}^{133}\mathrm{Cs}$ and ${}^{87}\mathrm{Rb}$${}^{133}\mathrm{Cs}$ isotopologues were obtained from Fourier-transform spectra of laser-induced fluorescence (LIF) from the $B\hspace{0.5em}{}^1\Pi$ and $(4){}^1\Sigma {}^{+}$ states to the $a\hspace{0.5em}{}^3\Sigma {}^{+}$ (4549 transitions) and $X\hspace{0.5em}{}^1\Sigma {}^{+}$ (15 709 transitions) states. The $X\hspace{0.5em}{}^1\Sigma {}^{+}$ state data were complemented by about 15 500 transitions obtained by Fellows et al. [J. Mol. Spectrosc. 197, 19 (1999)]. LIF progressions to the $a\hspace{0.5em}{}^3\Sigma {}^{+}$ state range from $v_a=0$ to 37, reaching an outer turning point at 15.97 Å. For the $X\hspace{0.5em}{}^1\Sigma {}^{+}$ state, by analyzing LIF from the shelflike $(4){}^1\Sigma {}^{+}$, the data are extended from $v_x=119$ as observed in the above-cited paper to $v_x=129$, extending the outer turning point from 10.7 to 17.55 Å. From these data, potential energy curves were constructed simultaneously for both hyperfine coupled states $X\hspace{0.5em}{}^1\Sigma {}^{+}$ and $a\hspace{0.5em}{}^3\Sigma {}^{+}$ in a coupled-channels fitting routine. This allowed us to accurately model the potential close to the Rb(5$s$) $+$ Cs(6$s$) atom-pair asymptote, which is required to simulate cold collision processes and to analyze the Feshbach resonances observed for ${}^{87}\mathrm{Rb}$${}^{133}\mathrm{Cs}$ by Pilch et al. [Phys. Rev. A 79, 042718 (2009)]. Dissociation energies were determined for the $X\hspace{0.5em}{}^1\Sigma {}^{+}$ state as $D_e=3836.373(40)$ cm${}^{-1}$ and for the $a\hspace{0.5em}{}^3\Sigma {}^{+}$ state as $D_e=259.341(30)$ cm${}^{-1}$.

We develop the theory of radiative association of an atom and a diatomic molecule within a close-coupling framework. We apply it to the formation of $\mathrm{H}{}_3{}^{-}$ after the low-energy collision (below 0.5 eV) of ${\mathrm{H}}_2$ with ${\mathrm{H}}^{-}$. Using recently obtained potential energy and permanent dipole moment surfaces of $\mathrm{H}{}_3{}^{-}$, we calculate the lowest rovibrational levels of the $\mathrm{H}{}_3{}^{-}$ electronic ground state and the cross section for the formation of $\mathrm{H}{}_3{}^{-}$ by radiative association between ${\mathrm{H}}^{-}$ and ortho- and para-H${}_2$. We discuss the possibility for the $\mathrm{H}{}_3{}^{-}$ ion to be formed and observed in the cold and dense interstellar medium in an environment with a high ionization rate. Such an observation could be a probe for the presence of ${\mathrm{H}}^{-}$ in the interstellar medium.

Making use of the Bloch density matrix technique, we derive exact analytical expressions for the density profile in Fourier space, for the current density and the so-called integrated current for fermionic systems confined by a two-dimensional harmonic oscillator, in the presence of a magnetic field or in a rotating trap of arbitrary strength. We present numerical, illustrative examples with or without magnetic field (with or without rotation).

We investigate the lowest scattering state of a one-dimensional Bose gas with attractive interactions trapped in a hard-wall trap. By solving the Bethe ansatz equation numerically, we determine the full energy spectrum and the exact wave function for different attractive interaction parameters. The resultant density distribution, momentum distribution, reduced one-body density matrix, and two-body correlation show that a decreased attractive interaction induces rich density profiles and specific correlation properties in the weakly attractive Bose gas.

We report the magnetic merging of ultracold atomic gases of ${}^{85}\mathrm{Rb}$ and ${}^{87}\mathrm{Rb}$ by the controlled overlap of two initially spatially separated magnetic traps. We present a detailed analysis of the combined magnetic-field potential as the two traps are brought together that predicts a clear optimum trajectory for the merging. We verify this prediction experimentally using ${}^{85}\mathrm{Rb}$ and find that the final atom number in the merged trap is maximized with minimal heating by following the predicted optimum trajectory. Using the magnetic-merging approach allows us to create variable-ratio isotopic Rb mixtures with a single laser-cooling setup by simply storing one isotope in a magnetic trap before jumping the laser frequencies to the transitions necessary to laser cool the second isotope.