arXiv subjects

Thomas Bergeman

Publications and source records attributed to Thomas Bergeman.

4 recordsLinked to original sources

arXiv2011

Phase Coherence and Fragmentation of Two-Component Bose-Einstein Condensates Loaded in State-Dependent Optical Lattices

A binary mixture of interacting Bose-Einstein condensates (BEC) in the presence of fragmentation-driving external lattice potentials forms two interdependent mean-field lattices made of each component. These effective mean-field lattices, like ordinary optical lattices, can induce additional fragmentation and phase coherence loss of BECs between lattice sites. In this study, we consider the nonequilibrium dynamics of two hyperfine states of one-dimensional Bose-Einstein condensates, subjected to state-dependent optical lattices. Our numerical calculations using the truncated Wigner approximation (TWA) show that phase coherence in a mixture of two-component BECs can be lost not just by optical lattices, but by mean-field lattices gradually formed by other components, and we reveal that such an effect of internal mean-field lattices, however, is limited, contrary to external optical lattices, in regard to phase decoherence.

cond-mat.quant-gas↗

arXiv2004

Production and state-selective detection of ultracold, ground state RbCs molecules

Using resonance-enhanced two-photon ionization, we detect ultracold, ground-state RbCs molecules formed via photoassociation in a laser-cooled mixture of 85Rb and 133Cs atoms. We obtain extensive bound-bound excitation spectra of these molecules, which provide detailed information about their vibrational distribution, as well as spectroscopic data on the RbCs ground a^3Σ^+ and excited (2)^3Σ^+, (1)^1Πstates. Analysis of this data allows us to predict strong transitions from observed excited levels to the absolute vibronic ground state of RbCs, potentially allowing the production of stable, ultracold polar molecules at rates as large as 10^7 s^{-1}.

physics.atom-ph↗

arXiv2003

Production of Ultracold, Polar RbCs* Molecules via Photoassociation

We have produced ultracold, polar RbCs* molecules via photoassociation in a laser-cooled mixture of Rb and Cs atoms. Using a model of the RbCs* molecular interaction which reproduces the observed rovibrational structure, we infer decay rates in our experiments into deeply bound singlet ground state RbCs vibrational levels as high as 5 x 10^5 s^-1 per level. Population in such deeply bound levels could be efficiently transferred to the vibrational ground state using a single stimulated Raman transition, opening the possibility to create large samples of stable, ultracold polar molecules.

physics.atom-ph↗

arXiv2001

Trends in Resonance Energy Shifts and Decay Rates for Bose Condensates in a Harmonic Trap

This is a study of quasi-discrete Bogoliubov quasi-particles in a spherically symmetric harmonic trap. We first evaluate analytically the aymptotic energy shifts of the high energy modes and find them to have $1/sqrt(n)$ dependence on the number of radial nodes, $n$, consistent with earlier semiclassical discussions. To address the question of the widths or decay rates, we attempt to clarify previous discussions by deriving an implicit equation for the widths from an assumption of exponential decay. Numerically, we study the trends in the behavior of the widths as a function of temperature, energy, particle number and scattering lengths. In particular, we find that the width due to Landau decay rises rapidly at low $n$ and then declines, while the Beliaev decay rate rises slowly with $n$. As temperature goes to zero, Beliaev decay reaches a constant (>0 for n>0), while the Landau decay rate goes to zero. The decay rate is approximately linear in the s-wave scattering length.

cond-mat.stat-mech↗