Dynamics, dephasing and clustering of impurity atoms in Bose-Einstein condensates

TL;DR

This paper explores how a Bose-Einstein condensate affects impurity atoms in an optical lattice, revealing effects on qubit dephasing, impurity clustering, and transport behavior, with implications for quantum information and many-body physics.

Contribution

It derives a quantum master equation for impurity atoms in a BEC, characterizes dephasing effects, and uncovers a phase transition leading to impurity clustering at realistic temperatures.

Findings

Observable qubit dephasing due to interspecies coupling

Impurities form a macroscopic cluster at certain temperatures

Transition from coherent to diffusive transport with increasing interaction

Abstract

We investigate the influence of a Bose-Einstein condensate (BEC) on the properties of immersed impurity atoms, which are trapped in an optical lattice. Assuming a weak coupling of the impurity atoms to the BEC, we derive a quantum master equation for the lattice system. In the special case of fixed impurities with two internal states the atoms represent a quantum register and the quantum master equation reproduces the exact evolution of the qubits. We characterise the qubit dephasing which is caused by the interspecies coupling and show that the effect of sub- and superdecoherence is observable for realistic experimental parameters. Furthermore, the BEC phonons mediate an attractive interaction between the impurities, which has an important impact on their spatial distribution. If the lattice atoms are allowed to move, there occurs a sharp transition with the impurities aggregating in a macroscopic cluster at experimentally achievable temperatures. We also investigate the impact of the BEC on the transport properties of the impurity atoms and show that a crossover from coherent to diffusive behaviour occurs with increasing interaction strength.