A Cold-Atom Ratchet Interpolating Between Classical and Quantum Dynamics

Abstract

We use an atomic ratchet realized by applying short pulses of an optical standing-wave to a Bose-Einstein condensate to study the crossover between classical and quantum dynamics. The signature of the ratchet is the existence of a directed current of atoms, even though there is an absence of a net bias force. Provided that the pulse period is close to one of the resonances of the system, the ratchet behavior can be understood using a classical like theory which depends on a single variable containing many of the experimental parameters. Here we show that this theory is valid in both the true classical limit, when the pulse period is close to zero, as well as regimes when this period is close to other resonances where the usual scaled Planck's constant is nonzero. By smoothly changing the pulse period between these resonances we demonstrate how it is possible to tune the ratchet between quantum and classical types of behavior.

Initial-state dependence of a quantum resonance ratchet

“…Our experimental apparatus is similar to the one described in Ref. [24]. A BEC with about 70,000 87 Rb atoms was created in the 5S 1/2 , F = 1 hyperfine ground states in a focused CO 2 laser beam using an all-optical trapping technique [35].…”

Hamiltonian Ratchets with Ultra‐Cold Atoms

“…The setup and procedure for the off‐resonance experiments were quite similar to those for quantum resonance, although the kicking pulse length was a little longer at 1.54 μs . The experiments were carried out using values of τ close to the zeroth () and first () quantum resonances.…”

“…[24,26,[38][39][40][41][42]. The stability of the ratchet is reviewed here for a broad range in the detuning of the drive from the exact resonance conditions, see also [30,43,44]. All the ratchets described here are non-dissipative, and the symmetry breaking necessary for the production of a net current arises from choosing asymmetric initial states with respect to the kicking potential.…”