Entanglement with a mode observable via a tunable interaction with a qubit

TL;DR

This paper proposes a tunable interaction scheme with a qubit to detect entanglement between a spin and a bosonic mode, overcoming symmetry limitations of previous fixed-coupling methods, and demonstrates its feasibility in superconducting qubits.

Contribution

It introduces a tunable coupling approach enabling detection of spin-boson entanglement via qubit measurements, which was not possible with fixed interactions.

Findings

Detection scheme works at finite temperatures.

Proposed parameters are feasible for superconducting transmon qubits.

Signal remains significant despite environmental symmetries.

Abstract

We study the possibility of detection of ``spin-boson'' entanglement by qubit only measurements. Such entanglement is impossible to detect by previously proposed schemes that involve a fixed system-environment interaction, because of inherent symmetries within the coupling and the initial state of the environment. We take advantage of the possibility of tuning of qubit-environment coupling, that is available in some qubit realizations. As an example we study a superconducting transmon qubit interacting with a microwave cavity, which is one of such systems and is, furthermore, essential in the context of quantum information processing. We propose suitable Hamiltonian parameters for the preparation and measurement phases of the detection scheme that allow for an experimental test, and verify that the reported signal is nonnegligibly large still at finite temperatures.