Preserving coherent spin and squeezed spin states of a spin-1 Bose-Einstein condensate with rotary echoes

摘要

A challenge in precision measurement with squeezed spin state arises from thespin dephasing due to stray magnetic fields. To suppress such environmentalnoises, we employ a continuous driving protocol, rotary echo, to enhance thespin coherence of a spin-1 Bose-Einstein condensate in stray magnetic fields.Our analytical and numerical results show that the coherent and the squeezedspin states are preserved for a significantly long time, compared to the freeinduction decay time, if the condition $h\tau = m\pi$ is met with $h$ the pulseamplitude and $\tau$ pulse width. In particular, both the spin average and thespin squeezing, including the direction and the amplitude, are simultaneouslyfixed for a squeezed spin state. Our results point out a practical way toimplement quantum measurements based on a spin-1 condensate beyond the standardquantum limit.