Dmytro Pesin (U. Virginia)
Coherence properties of a Raman-coupled pseudospin-1/2 BEC 

We consider the dynamics of first- and second-order coherences for two Raman-coupled Bose-Einstein condensates. This system was proposed to host a stripe phase with supersolid properties in Li et al., Nature, 543, 91-94 (2017). We show that the existence of the stripes - density modulation induced by the Raman lasers - is determined by the first order coherence between dressed condensates. It typically exists in single-shot experiments, but is a transient phenomenon if averaged over many measurements. However, the Brag scattering signal, actually studied in the work by Li et al., is determined by the second-order coherence, and exists even at long times.