MHz few-body frequency shift detected in a cold85Rb Rydberg gas

Abstract

We have observed a density-dependent frequency shift of more than 4 MHz in a cold ${}^{85}$Rb Rydberg gas trapped in a magneto-optical trap. A one-dimensional linearly aligned four-body model is proposed to explain the experimental data, and the calculation matches the experimental data. The calculation also shows that if the energy detuning between the two coupled states, the $nsnsns(n+1)s$ and $nsnsnpnp$ states in this case, is small, the lowest level of the $nsnsnpnp$ manifold has the maximum mixing probability, causing a frequency shift instead of line broadening. The results reported may be used for few-body blockade, Rydberg single-atom imaging, studying few-body to many-body transitions and interactions, and few-body ionization as well as quantum metrology.