Quantum spin dynamics of individual neutral impurities coupled to a Bose-Einstein condensate

TL;DR

This study investigates the spin dynamics of individual neutral impurities in a Bose-Einstein condensate, revealing how impurities interact with the condensate and maintain coherence, enabling non-destructive quantum probing.

Contribution

It demonstrates the controlled spin-exchange and coherence preservation of impurities in a BEC, advancing understanding of impurity-bath interactions in quantum gases.

Findings

Spin-exchange dynamics are dominated by the condensate fraction.

Impurity coherence remains unaffected despite high bath densities.

Spatial overlap of impurities and gas is resolved via spin-population measurements.

Abstract

We report on spin dynamics of individual, localized neutral impurities immersed in a Bose-Einstein condensate. Single Cesium atoms are transported into a cloud of Rubidium atoms, thermalize with the bath, and the ensuing spin-exchange between localized impurities with quasi-spin $F_i=3$ and bath atoms with $F_b=1$ is resolved. Comparing our data to numerical simulations of spin dynamics we find that, for gas densities in the BEC regime, the dynamics is dominated by the condensed fraction of the cloud. We spatially resolve the density overlap of impurities and gas by the spin-population of impurities. Finally we trace the coherence of impurities prepared in a coherent superposition of internal states when coupled to a gas of different densities. For our choice of states we show that, despite high bath densities and thus fast thermalization rates, the impurity coherence is not affected by the bath, realizing a regime of sympathetic cooling while maintaining internal state coherence. Our work paves the way toward non-destructive probing of quantum many-body systems via localized impurities.