1202.5174 (T. Salger et al.)

Coherent negative mobility of ultracold atoms in an optical lattice    [PDF]

T. Salger, S. Kling, S. Denisov, A. V. Ponomarev, P. Hanggi, M. Weitz

The paradoxical response, when a system produces an output - current, flux or
rotation - in the direction opposite to an applied bias or torque, seemingly
contradicts Newton's second law. Nevertheless, such a response, termed absolute
negative mobility, can occur in a system driven far out of thermal equilibrium.
In earlier works, the presence of strong decoherence mechanisms was regarded as
a prerequisite for negative mobility to appear. Here we report an experimental
and theoretical study showing absolute negative mobility in a fully coherent
quantum regime. Using a rubidium Bose-Einstein condensate loaded in a
time-periodically modulated optical lattice, we observe a negative response
from a coherent quantum system. The experimental results are explained in terms
of eigenstates of a time-periodic Hamiltonian. Our findings open new
possibilities for the control of quantum transport in the decoherence-free
limit.

View original: http://arxiv.org/abs/1202.5174