Spectroscopic insensitivity to cold collisions in a two-state mixture of fermions

TL;DR

This paper demonstrates that spectroscopic resonance shifts are absent in a mixture of two interacting Fermi gases, revealing insensitivity to cold collisions and coherence effects, supported by experimental results and theoretical explanation.

Contribution

It provides the first experimental evidence of spectroscopic insensitivity to cold collisions in a two-state fermionic mixture and offers a theoretical understanding of coherence effects on such systems.

Findings

No resonance shifts observed in two-state Fermi gas mixture

Resonance shift in bosons is coherence-independent and twice the energy splitting

Theoretical model explains the effect of coherent radiation on incoherent mixtures

Abstract

We have experimentally demonstrated the absence of spectroscopic resonance shifts in a mixture of two interacting Fermi gases. This result is linked to observations in an ultracold gas of thermal bosons. There, the measured resonance shift due to interstate collisions is independent of the coherence in the system, and twice that expected from the equilibrium energy splitting between the two states in a fully decohered cloud. We give a simple theoretical explanation of these observations, which elucidates the effect of coherent radiation on an incoherent mixture of atoms.