Geometric optics with atomic beams scattered by a detuned standing laser wave

We report on theoretical and numerical study of propagation of atomic beams crossing a detuned standing-wave laser beam in the geometric optics limit. The interplay between external and internal atomic degrees of freedom is used to manipulate the atomic motion along the optical axis by light. By adjusting the atom-laser detuning, we demonstrate how to focus, split and scatter atomic beams in a real experiment. The novel effect of chaotic scattering of atoms at a regular near-resonant standing wave is found numerically and explained qualitatively. Some applications of the effects found are discussed

Angular Spectrum of Acoustic Pulses at Long Ranges

Long-range propagation of sound pulses in the deep ocean is considered. A new method for the estimation of the pulse angular spectrum is presented. The method is based on the Husimi transform of a wave field and can be realized with a short vertical array of nondirectional hydrophones. As a result, one obtains a diagram of the arrival pattern in the time–angle plane. The method is applied to a model of the underwater sound channel in the Sea of Japan. Special attention is paid to sound scattering on a cold synoptic eddy along the waveguide. It is shown that the synoptic eddy leads to a splitting of the individual ray’s arrivals into clusters with close angles and times. The random sound-speed perturbation induced by internal waves blurs these clusters into a fuzzy background and simultaneously broaden the angular spectrum of pulses. Nevertheless, it is found that the latter effect is relatively weak for short vertical arrays. In particular, it is shown that increasing the array length from 10 to 30 m results in the separation of the arrivals with opposite angles

Quantum transport in a driven disordered potential: onset of directed current and noise-induced current reversal

We study motion of a quantum wavepacket in a one-dimensional potential with correlated disorder. Presence of long-range potential correlations allows for existence of both localized and extended states. Weak time-dependent perturbation in the form of a fluctuating plane wave is superimposed onto the potential. This model can be realized in experiments with optically trapped cold atoms. Time-dependent perturbation causes transitions between localized and extended states. Owing to violation of space-time symmetries, there arises atomic current which is codirectional with the wave-like perturbation. However, it is shown that the perturbation can drag atoms only within some limited time interval, and then the current changes its direction. Increasing of the perturbation bandwidth and/or amplitude results in decreasing of the time of current reversal. We argue that onset of the current reversal is associated with inhomogeneity of diffusion in the momentum space

Transport through degenerate tori and quantum-to-classical crossover in a driven Aubry-Andre model

Dynamics of ultracold atoms in a one-dimensional incommensurate quasiperiodic optical lattice is considered. The lattice is created as superposition of a large-amplitude primary lattice and a small-amplitude secondary lattice. In the tight-binding approximation motion of atoms is described by the Aubry-Andre model. Attention is focused on atom delocalization caused by amplitude modulation of the secondary lattice. We consider the semiclassical regime that is realized if the lattice spacing of the primary lattice is small compared to that of the secondary one. It is shown that efficient delocalization occurs if frequency of the modulation corresponds to resonant influence on degenerate tori in classical phase space. Inclusion of the next-to-nearest tunneling into the Aubry-Andre model leads to shift of the corresponding resonance to the lower frequency range. As ratio of primary and secondary lattice periods increases, effect of the resonance ceases