Anomalous Doppler effect in two-component Bose-Einstein condensates

TL;DR

This paper predicts and proposes a method to observe an anomalous Doppler effect in two-component Bose-Einstein condensates with persistent currents, highlighting the role of inter-species interactions.

Contribution

It provides an analytic framework and a measurement protocol for the anomalous Doppler effect in two-component BECs, extending previous superfluid helium studies.

Findings

Analytic predictions of non-trivial Doppler shifts due to inter-species interactions.

Proposed experimental protocol for measuring the effect.

Simulation results using coupled Gross-Pitaevskii equations.

Abstract

We show that two-component Bose-Einstein condensed mixtures, in presence of a persistent current, exhibit a non trivial Doppler shift of the sound velocities. The peculiarity is due to the inter-species interaction and the possibility of generating a counter-flow persistent current. Analytic predictions are derived by using superfluid hydrodynamics. While the existence of anomalous Doppler shifts at finite temperature has been discussed a long time ago in the case of superfluid Helium-4, an experimental verification of the effect is still missing. For this reason, we also propose a protocol for the measurement of the Doppler shifts, based on the density-density response function. The dynamical protocol is simulated by means of coupled Gross-Pitaevskii equations.