Mobile impurity probing a two-dimensional superfluid phase transition

The use of atomically sized quantum systems as highly sensitive measuring devices represents an exciting and quickly growing research field. Here we explore the properties of a quasiparticle formed by a mobile impurity interacting with a two-dimensional fermionic superfluid. The energy of the quasiparticle is shown to be lowered by superfluid pairing, as this increases the compressibility of the Fermi gas, thereby making it easier for the impurity to perturb its surroundings. We demonstrate that the fundamentally discontinuous nature of the superfluid-to-normal phase transition of a two-dimensional system leads to a rapid increase in the quasiparticle energy around the critical temperature. The magnitude of this increase exhibits a nonmonotonic behavior as a function of the pairing strength with a sizable maximum in the crossover region, where the spatial extend of the Cooper pairs is comparable to the interparticle spacing. Since the quasiparticle energy is measurable with present experimental techniques, our results illustrate how impurities entangled with their environment can serve as useful probes for nontrivial thermal and quantum correlations.

Automated summary

The properties of a quasiparticle formed by a mobile impurity interacting with a two-dimensional fermionic superfluid are explored. It is found that the energy of the quasiparticle is lowered by superfluid pairing, leading to an increase in its compressibility and making it easier for the impurity to perturb its surroundings. The discontinuous nature of the superfluid-to-normal phase transition in a two-dimensional system results in a rapid increase in the quasiparticle energy around the critical temperature. The magnitude of this increase shows nonmonotonic behavior with a maximum in the crossover region where the spatial extent of the Cooper pairs is comparable to the interparticle spacing. Since the quasiparticle energy can be measured with current experimental techniques, impurities entangled with their environment can serve as useful probes for studying nontrivial thermal and quantum correlations.