Quantum dynamics of an instabiltiy-induced pulsation in a Bose-Einstein condensate in an optical lattice

Uttam Shrestha, Juha Javanainen, Janne Ruostekoski

We study quantum dynamics of a Bose-Einstein condensate in a one-dimensional optical lattice in the limit of weak atom-atom interactions within the truncated Wigner approximation for a system with one dynamically unstable mode. This extends previous classical studies of a pulsating dynamical instability in which atoms periodically collect together and subsequently disperse back into the initial homogeneous state. We observe that the quasiperiodic behavior still persists in the presence of quantum fluctuations for a single realization that represents a typical experimental outcome, but ensemble averages show various manifestations of quantum statistics. Quantum effects become more prominent when the effective interaction strength is increased.

Sarah B. McKinney

M. K. H. Ome, Thomas M. Bersano, Sean M. Mossman +3 more

Uttam Shrestha

We study the dynamics of a Bose-Einstein condensate (BEC) in a one dimensional optical lattice in the limit of weak atom-atom interactions. Numerically we find that a BEC may develop a pulsating instability in which atoms nearly periodically collect themselves into a pulse and subsequently disperse back into the initial homogeneous state. A qualitative explanation of the quasi-periodic behavior is given by drawing an analogy with a double-well system. In an extension we introduce quantum effects approximately within Truncated Wigner Approximation (TWA). In pure classical mean field theory the condensate shows an undamped pulsating instability, whereas we have observed a damping in the oscillation when we average over many stochastic realizations.

W. C. Wu, Chou-Chun Huang

Uttam Shrestha, Marijan Koštrun, Juha Javanainen

We find numerically that in the limit of weak atom-atom interactions a Bose-Einstein condensate in an optical lattice may develop a pulsating dynamical instability in which the atoms nearly periodically form a peak in the occupation numbers of the lattice sites, and then return to the unstable initial state. Multiple peaks behaving similarly are also found. Simple arguments show that the pulsating instability is a remnant of integrability, and give a handle on the relevant physical scales.