Superfluid gyroscope with cold atomic gases

A trapped Bose-Einstein condensed atomic gas containing a quantized vortex is predicted to exhibit precession after a sudden rotation of the confining potential. The equations describing the motion of the condensate are derived and the effects of superfluidity explicitly pointed out. The dependence of the precession frequency on the relevant parameters of the problem is discussed. The proposed gyroscope is well suited to explore rotational effects at the level of single quanta of circulation.     

Resonantly enhanced continuous-wave four-wave mixing with spontaneously generated coherence in a five-state cold atomic medium

Using Schroedinger-Maxwell formalism, we propose and analyse a continuous-wave four-wave mixing (FWM) scheme for the generation of coherent light in a five-state double-A atomic system with or without spontaneously generated coherence (SGC) based on electromagnetically induced transparency (EIT). We derive the corresponding explicit analytical expressions for the generated FWM field under the steady-state condition. The influence of hyperfine sublevel and SGC effect on the amplitude of the generated FWM field is predicted in detail via the derived analytical expressions. We also give a brief discussion on the experimental realization of the proposed scheme.     

Weak dynamical localization in periodically kicked cold atomic gases

Quantum kicked rotor was recently realized in experiments with cold atomic gases and standing optical waves. As predicted, it exhibits dynamical localization in the momentum space. Here we consider the weak-localization regime concentrating on the Ehrenfest time scale. The latter accounts for the spread time of a minimal wave packet and is proportional to the logarithm of the Planck constant. We show that the onset of the dynamical localization is essentially delayed by four Ehrenfest times, and give quantitative predictions suitable for an experimental verification.     

Magnetic properties of degenerate atomic Fermi gases

Magnetic effects in a degenerate atomic Fermi gas, such as the exchange enhancement of the paramagnetic susceptibility and the existence of the phase transition to the ferromagnetic state with the spontaneous polarization of the atomic spins, are discussed. The propagation of spin waves in the atomic system is considered.     

Raman coupling and cooper pairing in cold atomic Fermi gases

We consider a cold two-species atomic Fermi gas confined in a trap. We combine the Hainan coupling between the states (we assume them to be the states with different spins) with the Cooper pairing of atoms with these different spins. This opens up a new prospect for investigation of interplay between various phenomena involving Raman coupling (e.g., atom lasers, dark-state polaritons) and effects caused by Cooper pairing of particles (e.g., superfluidity). We have obtained a threshold of transition from oscillatory to amplifying behavior of matter waves.     

Coherence length of cold exciton gases in coupled quantum wells

A Mach-Zehnder interferometer with spatial and spectral resolution was used to probe spontaneous coherence in cold exciton gases, which are implemented experimentally in the ring of indirect excitons in coupled quantum wells. A strong enhancement of the exciton coherence length is observed at temperatures below a few Kelvin. The increase of the coherence length is correlated with the macroscopic spatial ordering of excitons. The coherence length at the lowest temperature corresponds to a very narrow spread of the exciton momentum distribution, much smaller than that for a classical exciton gas.     

Thermoelectric transport and Peltier cooling of cold atomic gases

This brief review presents the emerging field of mesoscopic physics with cold atoms, with an emphasis on thermal and ‘thermoelectric’ transport, i.e. coupled transport of particles and entropy. We review in particular the comparison between theoretically predicted and experimentally observed thermoelectric effects in such systems. We also show how combining well-designed transport properties and evaporative cooling leads to an equivalent of the Peltier effect with cold atoms, which can be used as a new cooling procedure with improved cooling power and efficiency compared to the evaporative cooling currently used in atomic gases. This could lead to a new generation of experiments probing strong correlation effects of ultracold fermionic atoms at low temperatures.     

Longitudinal coherence length of an optical field

Longitudinal coherence of an optical field depending on the parameters of its frequency and angular spectra is considered. Expressions for the function and length of longitudinal coherence depending on the width of the frequency and angular spectra are obtained. The competitive influence of the angular and frequency spectra of the field on its longitudinal coherence is discussed. Experimental studies using a longitudinal shearing Michelson interferometer that proves theoretical results are performed.     

Manipulation of slow light with orbital angular momentum in cold atomic gases

We study the propagation of a weak pulse of slow light in a cloud of cold atoms controlled by two additional laser beams of larger intensity in a tripod configuration of the light-matter coupling. We consider a case where one of the control beams has an optical vortex and thus has a zero intensity at the center. The presence of the second control beams restores adiabaticity in the propagation of the probe beam. This makes it possible to exchange the optical vortex between the control and probe fields during the storage. We analyze conditions for the vortex of the control beam to be transferred efficiently to the restored probe beam.     

Effect of superradiance on transport of diffusing photons in cold atomic gases

We show that in atomic gases cooperative effects like superradiance and subradiance lead to a potential between two atoms that decays like 1/r. In the case of superradiance, this potential is attractive for close enough atoms and can be interpreted as a coherent mesoscopic effect. The contribution of superradiant pairs to multiple scattering properties of a dilute gas, such as photon elastic mean free path and group velocity, is significantly different from that of independent atoms. We discuss the conditions under which these effects may be observed and compare our results to recent experiments on photon transport in cold atomic gases.     

Three-mode entanglement via atomic coherence induced by strong classical field

We propose a new scheme to achieve fully three-mode entanglement based on the standard criteria [P. van Loock and A. Furusawa, Phys. Rev. A 67, 052315 (2003)] in a four-level atomic system driven by two strong classical fields. Via numerically simulating the dynamics of the system, we investigate the generation and evolution of entanglement. Based on our scheme, it is demonstrated that the three-mode continuous-variable (CV) entanglement can be achieved under different initial conditions and the entangled period will be extended by enhancing the intensity of the classical field. Moreover, our numerical results also show that the present system can be considered as a three-mode entanglement amplifier.     

Creation of an effective magnetic field in ultracold atomic gases using electromagnetically induced transparency

We consider the influence of the control and probe beams in the electromagnetically induced transparency configuration on the mechanical motion of ultracold atomic gases (atomic Bose-Einstein condensates or degenerate Fermi gases). We carry out a microscopic analysis of the interplay between radiation and matter and show that the two beams of light can provide an effective magnetic field acting on electrically neutral atoms in the case where the probe beam has an orbital angular momentum. As an example, we demonstrate how a Meissner-like effect can be created in an atomic Bose-Einstein condensate.     

Phase fluctuations in atomic Bose gases

We improve on the Popov theory for partially Bose-Einstein condensed atomic gases by treating the phase fluctuations exactly. As a result, the theory becomes valid in arbitrary dimensions and is able to describe the low-temperature crossover between three-, two-, and one-dimensional Bose gases, which is currently being explored experimentally. We consider both homogeneous and trapped Bose gases.     

Thermalization of atomic particles in gases

A model of the atomic particle thermalization process due to scattering in various gases with application of the Born-Mayer potential is presented. The thermalization process of atomic particles using the statistical modeling method is considered. Our thermalization model is adapted to a wide class of atomic collision partners, takes into account the real energy and angular distributions of atomic particle sources, and makes it possible to calculate the parameters of the spatial zone of their thermalization and transfer into the diffusion motion mode. The energy range of applicability for the atomic particle thermalization model is interesting for many applied problems in plasma physics, gas discharge, and ion plating processes.     

Slow light in ultra-cold atomic gases

We investigate the influence of slow light with an orbital angular momentum on the mechanical motion of ultra-cold atomic gases including both the atomic Bose–Einstein condensates and degenerate Fermi gases. We present a microscopic analysis of the interplay between light and matter and show how slow light can provide an effective magnetic field acting on the electrically neutral atoms.     

Resonant positronium formation in atomic gases

A method is presented for calculation of quasistationary excited states of positronium ions. These states are treated as bound positron states in the quadrupole field of an excited valence electron, which are capable of decaying both with positron emission into the continuous spectrum, and with positronium emission. The existence of such states should manifest itself in resonances in the positronium formation section upon motion of positrons with energy in the eV range. The resonant section parameters are calculated for a number of atoms.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 6–12, March, 1984.