Detection of the phase shift of an alternating-current magnetic field by quantum sensing with multiple-pulse decoupling sequences

TL;DR

This paper demonstrates that NV center quantum sensors with multiple-pulse decoupling sequences can detect both the amplitude and phase shifts of AC magnetic fields, enabling highly sensitive measurements of complex fields at microscopic scales.

Contribution

It reveals that non-phase-accumulation conditions can be used to detect small phase shifts, advancing the capabilities of quantum magnetometry with NV centers.

Findings

NV quantum sensing can measure phase shifts of AC magnetic fields.

Non-phase-accumulation conditions enable detection of small phase differences.

The method improves sensitivity for complex magnetic field measurements.

Abstract

Magnetometry utilizing a spin qubit in a solid state possesses high sensitivity. In particular, a magnetic sensor with a high spatial resolution can be achieved with the electron-spin states of a nitrogen vacancy (NV) center in diamond. In this study, we demonstrated that NV quantum sensing based on multiple-pulse decoupling sequences can sensitively measure not only the amplitude but also the phase shift of an alternating-current (AC) magnetic field. In the AC magnetometry based on decoupling sequences, the maximum phase accumulation of the NV spin due to an AC field can be generally obtained when the $\pi$-pulse period in the sequences matches the half time period of the field and the relative phase difference between the sequences and the field is zero. By contrast, the NV quantum sensor acquires no phase accumulation if the relative phase difference is $\pi/2$. Thus, this phase-accumulation condition does not have any advantage for the magnetometry. However, we revealed that the non-phase-accumulation condition is available for detecting a very small phase shift of an AC field from its initial phase. This finding is expected to provide a guide for realizing sensitive measurement of a complex AC magnetic field in micrometer and nanometer scales.