Unusual decoherence in qubit measurements with a Bose-Einstein condensate

TL;DR

This paper investigates how a Bose-Einstein condensate affects qubit coherence, revealing unusual slow and Gaussian decoherence patterns that differ from classical detector effects, with decoherence depending on initial states.

Contribution

It provides an analytical model of qubit decoherence near a BEC, highlighting non-exponential, incomplete decoherence behaviors and their dependence on initial conditions.

Findings

Qubit coherence decays as 1/√t, indicating slow damping.

Decoherence becomes Gaussian for static qubits.

Decoherence is incomplete and initial state-dependent.

Abstract

We consider an electrostatic qubit located near a Bose-Einstein condensate (BEC) of noninteracting bosons in a double-well potential, which is used for qubit measurements. Tracing out the BEC variables we obtain a simple analytical expression for the qubit's density-matrix. The qubit's evolution exhibits a slow ($\propto1/\sqrt{t}$) damping of the qubit's coherence term, which however turns to be a Gaussian one in the case of static qubit. This stays in contrast to the exponential damping produced by most classical detectors. The decoherence is, in general, incomplete and strongly depends on the initial state of the qubit.