Intrinsic and induced quantum quenches for enhancing qubit-based quantum noise spectroscopy

TL;DR

This paper explores how quantum quenches in sensing protocols can be harnessed to directly measure environmental properties and improve noise spectroscopy, especially in quantum systems like NV centers.

Contribution

It introduces methods to utilize environmental quenches for direct bath property measurements and bath spectral function reconstruction in quantum sensing.

Findings

Quenches affect sensor qubit evolution and reveal environmental response.

Protocols enable direct measurement of bath temperature and non-thermal states.

Techniques for controlling quenches improve spectral function reconstruction.

Abstract

We discuss how standard $T_2$-based quantum sensing and noise spectroscopy protocols often give rise to an inadvertent quench of the system or environment being probed: there is an effective sudden change in the environmental Hamiltonian at the start of the sensing protocol. These quenches are extremely sensitive to the initial environmental state, and lead to observable changes in the sensor qubit evolution. We show how these new features can be used to directly access environmental response properties. This enables methods for direct measurement of bath temperature, and methods to diagnose non-thermal equilibrium states. We also discuss techniques that allow one to deliberately control and modulate this quench physics, which enables reconstruction of the bath spectral function. Extensions to non-Gaussian quantum baths are also discussed, as is the direct applicability of our ideas to standard diamond NV-center based quantum sensing platforms.