How to detect qubit-environment entanglement generated during qubit dephasing

TL;DR

This paper introduces an experimental protocol to detect qubit-environment entanglement during dephasing using only qubit measurements, revealing quantum noise effects without direct environment measurement.

Contribution

It presents a simple, measurement-based protocol to identify entanglement generated during qubit dephasing, applicable to realistic quantum systems.

Findings

Protocol successfully detects entanglement in nitrogen vacancy center qubits.

Entanglement detection distinguishes quantum noise from classical noise.

Experimental feasibility demonstrated with realistic models.

Abstract

We propose a straightforward experimental protocol to test whether qubit-environment entanglement is generated during pure dephasing of a qubit. The protocol is implemented using only measurements and operations on the qubit - it does not involve the measurement of the system-environment state of interest, but the preparation and measurement of the qubit in two simple variations. A difference in the time dependencies of qubit coherence between the two cases testifies to the presence of entanglement in the state of interest. Furthermore, it signifies that the environment-induced noise experienced by the qubit cannot be modeled as a classical stochastic process independent of the qubit state. We demonstrate the operation of this protocol on a realistically modeled nitrogen vacancy center spin qubit in diamond interacting with a nuclear spin environment, and show that the generation of entanglement should be easily observable in this case.