NV-Diamond Magnetic Microscopy using a Double Quantum 4-Ramsey Protocol

TL;DR

This paper presents a double quantum 4-Ramsey protocol for NV-diamond magnetic microscopy, significantly improving sensitivity homogeneity and robustness over traditional methods, enabling better imaging of dynamic magnetic sources.

Contribution

The authors introduce a novel double quantum 4-Ramsey measurement protocol that enhances magnetic sensitivity homogeneity in NV-diamond imaging compared to conventional single quantum techniques.

Findings

Achieved volume-normalized DC magnetic sensitivity of 34 nTHz$^{-1/2} \, ext{μm}^{3/2}$

Reduced spatial variation in sensitivity by about 5 times

Enabled imaging of dynamic broadband magnetic sources

Abstract

We introduce a double quantum (DQ) 4-Ramsey measurement protocol that enables wide-field magnetic imaging using nitrogen vacancy (NV) centers in diamond, with enhanced homogeneity of the magnetic sensitivity relative to conventional single quantum (SQ) techniques. The DQ 4-Ramsey protocol employs microwave-phase alternation across four consecutive Ramsey (4-Ramsey) measurements to isolate the desired DQ magnetic signal from any residual SQ signal induced by microwave pulse errors. In a demonstration experiment employing a 1-$\mu$m-thick NV layer in a macroscopic diamond chip, the DQ 4-Ramsey protocol provides volume-normalized DC magnetic sensitivity of $\eta^\text{V}=34\,$nTHz$^{-1/2} \mu$m$^{3/2}$ across a $125\,\mu$m$ \,\times\,125\,\mu $m field of view, with about 5$\times$ less spatial variation in sensitivity across the field of view compared to a SQ measurement. The improved robustness and magnetic sensitivity homogeneity of the DQ 4-Ramsey protocol enable imaging of dynamic, broadband magnetic sources such as integrated circuits and electrically-active cells.