Fig. 1: Ramsey signal.
From: Tan’s two-body contact across the superfluid transition of a planar Bose gas
Example of an interferometric Ramsey signal showing the optical density of the fraction of the gas in state \(\left|2\right\rangle\) after the second Ramsey pulse, as a function of the microwave frequency ν. These data were recorded for \(\bar{n}\approx 40\) atoms/μm2 and T ~ 22 nK, τ1 = 10 ms. Here, τ2 has been increased to 1 ms to limit the number of fringes for better visibility. Inset. Filled black disks (resp. open red circles): central fringe for atoms in \(\left|2\right\rangle\) (resp. \(\left|1\right\rangle\)) in our standard configuration τ2 = 0.1 ms. The density in \(\left|1\right\rangle\) is obtained by applying a microwave π-pulse just before the absorption imaging phase. When atoms are maximally transferred in state \(\left|2\right\rangle\), we observe no significant population in state \(\left|1\right\rangle\), compatible with a full transfer induced by the Ramsey pulses. Blue squares: single-atom response measured during the ballistic expansion of the cloud by imaging atoms in \(\left|2\right\rangle\). The lines in the inset are sinusoidal fits to the data. The vertical error bars of the inset correspond to the standard deviation of the three repetitions made for this measurement.
