Quantum machine using cold atoms

TL;DR

This paper presents a minimal quantum motor using two cold atoms in a ring-shaped optical potential, demonstrating steady rotation and the ability to perform useful work under specific conditions.

Contribution

It introduces a simple two-atom quantum motor design that operates reliably regardless of initial timing, advancing practical quantum machine concepts.

Findings

The quantum motor achieves a steady, nonzero velocity independent of start time.

The system demonstrates rectification mechanisms enabling useful work.

The motor's velocity saturates with increasing system size.

Abstract

For a machine to be useful in practice, it preferably has to meet two requirements: namely, (i) to be able to perform work under a load and (ii) its operational regime should ideally not depend on the time at which the machine is switched-on. We devise a minimal setup, consisting of two atoms only, for an ac-driven quantum motor which fulfills both these conditions. Explicitly, the motor consists of two different interacting atoms placed into a ring-shaped periodic optical potential -- an optical "bracelet" --, resulting from the interference of two counter-propagating Laguerre-Gauss laser beams. This bracelet is additionally threaded by a pulsating magnetic flux. While the first atom plays a role of a quantum "carrier", the second serves as a quantum "starter", which sets off the "carrier" into a steady rotational motion. For fixed zero-momentum initial conditions the asymptotic carrier velocity saturates to a unique, nonzero value which becomes increasingly independent on the starting time with increasing "bracelet"-size. We identify the quantum mechanisms of rectification and demonstrate that our quantum motor is able to perform useful work.