Control of spin current in a Bose gas by bang-bang pulses

TL;DR

This paper demonstrates how bang-bang pulse sequences can control spin currents in a Bose-Einstein condensate, prolonging spin coherence and enabling potential quantum sensing applications despite the presence of spin currents.

Contribution

It introduces a method to control and extend spin coherence in a spinor Bose gas using periodic $$ pulses, a novel approach for managing spin dynamics in quantum gases.

Findings

Spin currents destroy spin polarization and induce two-body collisions.

Bang-bang control extends spin coherence times significantly.

Weak revival of spin coherence occurs due to in-trap oscillations.

Abstract

We generate spin currents in an $^{87}$Rb spin-2 Bose-Einstein condensate by application of a magnetic field gradient. The spin current destroys the spin polarization, leading to a sudden onset of two-body collisions. In addition, the spin coherence, as measured by the fringe contrast using Ramsey interferometry, is reduced drastically but experiences a weak revival due to in-trap oscillations. The spin current can be controlled using periodic $\pi$ pulses (bang-bang control), producing longer spin coherence times. Our results show that spin coherence can be maintained even in the presence of spin currents, with applications to quantum sensing in noisy environments.