Distinguishing Quantum and Classical Baths via Correlation Measurements

TL;DR

This paper proposes a measurement scheme to distinguish quantum from classical baths by detecting quantum backaction through correlation measurements, applicable to large spin systems like quantum dots.

Contribution

It introduces a novel correlation measurement method to identify quantum backaction in qubit-bath interactions, applicable to macroscopic systems.

Findings

Backaction detectable in large nuclear spin baths

Correlation dependence on qubit manipulation

Applicable to realistic quantum dot systems

Abstract

Investigations of quantum mechanical effects in macroscopic systems are of great interest to shed light onto the question where and how the transition to the classical world appears. It is also of practical relevance to determine if a bath dephasing a qubit can be described classically or requires a quantum mechanical treatment. We propose a measurement scheme to detect quantum backaction via correlation measurements to answer this question for a bath coupled to a single qubit. The presence of backaction leads to a dependence of correlations of subsequent initialization-evolution-readout cycles on how the qubit is manipulated in between. We compute the autocorrelation function for both an instructive spin model and the realistic case of an electron spin coupled to a bath of $10^6$ nuclear spins, as found in gated GaAs quantum dots, and show that backaction from the qubit onto the nuclear spin bath should be detectable even in such a large system.