# Quantum sensing with arbitrary frequency resolution

## TL;DR

This paper presents a quantum sensing method that achieves arbitrary frequency resolution using quantum lock-in detection with nitrogen vacancy centers, enabling highly sensitive magnetic field measurements over a broad bandwidth.

## Contribution

The authors introduce a novel quantum sensing approach with frequency resolution limited only by an external clock, demonstrated using NV centers for magnetic field detection.

## Key findings

- Achieved 70 μHz frequency resolution over MHz bandwidth.
- Demonstrated high sensitivity with SNR > 10,000:1 in one hour.
- Applicable to magnetic resonance and quantum simulation.

## Abstract

Quantum sensing takes advantage of well controlled quantum systems for performing measurements with high sensitivity and precision. We have implemented a concept for quantum sensing with arbitrary frequency resolution, independent of the qubit probe and limited only by the stability of an external synchronization clock. Our concept makes use of quantum lock-in detection to continuously probe a signal of interest. Using the electronic spin of a single nitrogen vacancy center in diamond, we demonstrate detection of oscillating magnetic fields with a frequency resolution of 70 uHz over a MHz bandwidth. The continuous sampling further guarantees an excellent sensitivity, reaching a signal-to-noise ratio in excess of 10,000:1 for a 170 nT test signal measured during a one-hour interval. Our technique has applications in magnetic resonance spectroscopy, quantum simulation, and sensitive signal detection.