Preparing Quantum Backflow States by Large Momentum Transfer

TL;DR

This paper proposes a method using large-momentum-transfer atom interferometry to prepare quantum backflow states in Bose-Einstein condensates, enabling tunable negative probability currents with minimal contamination.

Contribution

It extends previous single-pulse schemes by allowing multiple momentum-transfer pulses, enhancing backflow signatures in cold-atom experiments.

Findings

Protocol generates interference states with tunable probability current

Negligible negative-momentum contamination in realistic parameters

Parameter regimes identified where backflow signature is enhanced

Abstract

Quantum backflow refers to the appearance of negative probability current in a state whose momentum distribution is essentially positive. We propose a scheme to prepare such states in a noninteracting Bose-Einstein condensate using large-momentum-transfer (LMT) atom interferometry. Our approach extends the single-pulse proposal of Palmero et al. by allowing one interferometer arm to undergo a tunable sequence of momentum-transfer pulses before recombination with a freely propagating arm. For realistic parameters for Sr-88, the protocol generates interference states with tunable probability current and negligible negative-momentum contamination. We evaluate both the probability current and the critical-density criterion introduced by Palmero et al., and identify parameter regimes in which the backflow signature is enhanced relative to the single-pulse scheme. These results present LMT interferometry as a flexible route for preparing candidate quantum-backflow states in cold-atom experiments.