The Mystery of the Ramsey Fringe that Didn't Chirp

TL;DR

This paper uses microwave spectroscopy on ultra-cold 87Rb to measure density correlations and collision shifts, confirming the controversial factors of two in mean-field energies and exploring decoherence effects on inter-state interactions.

Contribution

It provides experimental verification of the factors of two in density correlations and collision shifts in ultra-cold rubidium, challenging naive expectations about decoherence effects.

Findings

Confirmed the presence of factors of two in mean-field energies.

Measured collision shifts for normal and condensed clouds.

Observed no expected frequency chirp during decoherence.

Abstract

We use precision microwave spectroscopy of magnetically trapped, ultra-cold 87Rb to characterize intra- and inter-state density correlations. The cold collision shifts for both normal and condensed clouds are measured. The results verify the presence of the sometimes controversial "factors of two", in normal-cloud mean-field energies, both within a particular state and between two distinct spin species. One might expect that as two spin species decohere, the inter-state factor of two would revert to unity, but the associated frequency chirp one naively expects from such a trend is not observed in our data.