Directed Transport of Atoms in a Hamiltonian Quantum Ratchet

TL;DR

This paper demonstrates a quantum ratchet effect using a Bose-Einstein condensate in a modulated optical lattice, showing quantum transport without dissipation and providing a proof of principle for a quantum motor.

Contribution

It presents the first experimental realization of a Hamiltonian quantum ratchet with atomic condensates, highlighting quantum effects in directed transport.

Findings

Atomic current oscillates around a non-zero stationary value.

Resonances are observed at photon recoil positions.

Transport depends on initial phase, confirming quantum behavior.

Abstract

We demonstrate the operation of a quantum ratchet in the absence of dissipative processes within the observation time (Hamiltonian regime). An atomic rubidium Bose-Einstein condensate is exposed to a sawtooth-like optical lattice potential, whose amplitude is periodically modulated in time. The ratchet transport arises from broken spatiotemporal symmetries of the driven potential, resulting in a desymmetrisation of transporting Eigenstates (Floquet states). The measured atomic current oscillates around a non-zero stationary value at longer observation times, shows resonances at positions determined by the photon recoil and depends on the initial phase of the drive, providing different lines of evidence for the full quantum character of the ratchet transport. The results provide a proof of principle demonstration of a quantum motor.