A fully controllable Kondo system: Coupling a flux qubit and an ultracold Fermi gas

TL;DR

This paper proposes a novel hybrid quantum system coupling a flux qubit with an ultracold Fermi gas to realize and study the Kondo effect, with potential for experimental observation and exploration of nonequilibrium dynamics.

Contribution

It introduces a fully controllable Kondo system combining superconducting qubits and ultracold atoms, enabling new experimental and theoretical investigations.

Findings

Formation of a Kondo state below the Kondo temperature.

Distinct momentum distribution signatures of the Kondo screening.

System's controllability allows exploration of nonequilibrium relaxation.

Abstract

We show that a composite spin-1/2 Kondo system can be formed by coupling a superconducting quantum interference device (SQUID) to the internal hyperfine states of a trapped ultracold atomic Fermi gas. Here, the SQUID, or flux qubit, acts as an effective magnetic impurity that induces spin-flip scattering near the Fermi energies of the trapped gas. Although the ultracold gas and SQUID are at vastly different temperatures, the formation of a strongly correlated Kondo state between the two systems is found when the gas is cooled below the Kondo temperature; this temperature regime is within current experimental limits. Furthermore, the momentum distribution of the trapped fermions is calculated. We find that it clearly contains an experimental signature of this correlated state and the associated Kondo screening length. In addition to probing Kondo physics, the controllability of this system can be used to systematically explore the relaxation and equilibration of a strongly correlated system that has been initially prepared in a selected nonequilibrium state.