[Paper Review] Locking and Tracking Magnetic Resonance Spectra of NV- Center for Real-time Magnetometry using a Differential Photon-Rate Meter

Kapildeb Ambal, R. D. McMichael|arXiv (Cornell University)|Aug 16, 2018

Diamond and Carbon-based Materials Research22 references4 citations

TL;DR

This paper presents a real-time magnetometry system using nitrogen-vacancy (NV−) centers in diamond, employing a differential photon-rate meter and active feedback to lock onto and track magnetic resonance peaks. It achieves ~6 μT/Hz¹/² sensitivity and tracks field changes at rates exceeding 110 μT/s, enabling continuous, high-bandwidth magnetic field sensing with automated data processing.

ABSTRACT

We describe a real-time data processing and frequency control method to track peaks in optically detected magnetic resonance of nitrogen-vacancy centers in diamond. This procedure allows us to measure magnetic field continuously with sensitivity ~6 uT/Hz^{1/2} and to track resonances at sweep rates exceeding 110 uT/s. We use a custom-built differential photon rate meter and active feedback control to "lock" the microwave excitation frequency of the magnetic resonance. Our scheme covers a broad magnetic field range, limited by the frequency range of the microwave generator. This measurement procedure automates the processing of voltage pulse outputs from the photon counters, and it provides sensitivity comparable to traditional photon counting methods

Motivation & Objective

• To enable continuous, real-time magnetic field sensing using NV− centers in diamond.
• To overcome limitations in traditional photon counting by automating data processing and feedback control.
• To achieve high sensitivity and fast tracking of magnetic resonance peaks under dynamic field conditions.
• To extend the operational range of NV−-based magnetometry using a tunable microwave source.

Proposed method

• A custom differential photon-rate meter is used to measure the difference in photon counts between two detection windows, enhancing signal-to-noise ratio.
• Active feedback control locks the microwave excitation frequency to the NV− center's resonance peak by comparing the differential signal to a reference.
• Voltage pulse outputs from photon counters are processed in real time to generate control signals for the microwave source.
• The system uses a tunable microwave generator to cover a broad magnetic field range, limited only by the generator's frequency bandwidth.
• The feedback loop continuously adjusts the microwave frequency to maintain resonance as the magnetic field changes.
• The method automates data processing, replacing manual peak detection and enabling real-time operation.

Experimental results

Research questions

• RQ1 Can a real-time feedback system maintain resonance lock on NV− center magnetic resonance under dynamic field conditions?
• RQ2 What is the achievable sensitivity and tracking bandwidth of a feedback-controlled NV− magnetometer using a differential photon-rate meter?
• RQ3 How does the differential photon-rate technique improve signal stability and measurement bandwidth compared to standard photon counting?
• RQ4 To what extent can the system track rapid magnetic field changes while maintaining high sensitivity?
• RQ5 Can automated, real-time processing replace manual data analysis in NV−-based magnetometry?

Key findings

• The system achieves a magnetic field sensitivity of approximately 6 μT/Hz¹/², comparable to traditional photon counting methods.
• The feedback system enables tracking of magnetic field changes at rates exceeding 110 μT/s, demonstrating high temporal resolution.
• The differential photon-rate meter reduces noise and improves signal stability, enabling reliable real-time operation.
• The method automates data processing of photon counter outputs, eliminating manual peak detection.
• The system operates over a broad magnetic field range, limited only by the microwave generator's frequency tuning range.
• The feedback loop successfully maintains resonance lock even during rapid field sweeps, ensuring continuous measurement.