Interaction-induced dynamical phase locking of Bose-Einstein condensates

We show that interactions result in the emergence of a {\it definite} relative-phase between two initially incoherent Bose-Einstein condensates. The many-realization interference fringe visibility is universal at $g_{12}^{(1)}\sim1/3$ throughout the Josephson interaction regime, as evident from a semiclassical picture. Other types of incoherent preparation yield qualitatively different coherence dynamics.Comment: 4 pages, 5 figure

Breakdown of the Internet under intentional attack

We study the tolerance of random networks to intentional attack, whereby a fraction p of the most connected sites is removed. We focus on scale-free networks, having connectivity distribution of P(k)~k^(-a) (where k is the site connectivity), and use percolation theory to study analytically and numerically the critical fraction p_c needed for the disintegration of the network, as well as the size of the largest connected cluster. We find that even networks with a<=3, known to be resilient to random removal of sites, are sensitive to intentional attack. We also argue that, near criticality, the average distance between sites in the spanning (largest) cluster scales with its mass, M, as sqrt(M), rather than as log_k M, as expected for random networks away from criticality. Thus, the disruptive effects of intentional attack become relevant even before the critical threshold is reached.Comment: Latex, 4 pages, 3 eps figure

Molecular Frisbee: Motion of Spinning Molecules in Inhomogeneous Fields

Several laser techniques have been suggested and demonstrated recently for preparing polarizable molecules in rapidly spinning states with a disc-like angular distribution. We consider motion of these spinning discs in inhomogeneous fields, and show that the molecular trajectories may be precisely controlled by the tilt of the plane of the laser-induced rotation. The feasibility of the scheme is illustrated by optical deflection of linear molecules twirled by two delayed cross-polarized laser pulses. These results open new ways for many applications involving molecular focusing, guiding and trapping, and may be suitable for separating molecular mixtures by optical and static fields

SYSTEM IDENTIFICATION IN THE WAVELET DOMAIN WITH CROSSBAND FILTERS

ABSTRACT In this paper, we present a wavelet domain system identification scheme, which takes into consideration the cross-terms between different frequency bands. Wavelet domain subband processing is advantageous whenever it produces a sparse representation of the processed signals. Perfect representation of linear time invariant (LTI) systems in the discrete-time wavelet transform (DTWT) domain requires time-invariant band-to-band filters and time-varying crossband filters between distnict subbands. We represent the response between two different subbands as a convolution with an appropriate multirate crossband filter. This reduces the model mismatch, which improves the identification in high SNR environment. The crossband filters formulation is extended to the twodimensional wavelet domain. Experimental results demonstrate the advantages of crossband filters usage

Confinement and lattice QED electric flux-tubes simulated with ultracold atoms

We propose a method for simulating 2+1-d compact lattice quantum-electrodynamics (QED), using ultracold atoms in optical lattices. In our model local Bose-Einstein condensates' phases correspond to the electromagnetic vector-potential, and the fluctuations of the local number operators represent the conjugate electric field. The gauge invariant Kogut-Susskind Hamiltonian is obtained as an effective low energy theory. The field is then coupled to external static charges. We show that in the strong coupling limit this gives rise to 'electric flux-tubes' and to confinement. The effect can be observed by measuring the local density fluctuations of the BECs