Enhancing Spin-Based Sensor Sensitivity by Avoiding Microwave Field Inhomogeneity of NV Defect Ensemble

Area of Science:

• Quantum sensing
• Solid-state physics
• Materials science

Background:

• Nitrogen-vacancy (NV) centers in diamond are promising quantum sensors.
• Achieving high magnetic field sensitivity requires optimizing NV center excitation and minimizing noise.

Purpose of the Study:

• To systematically study magnetic field sensitivity of NV centers.
• To design an optimal structure for microwave (MW) signal excitation.
• To improve the sensitivity of NV-based magnetometers.

Main Methods:

• Designed a structure with two parallel loop antennas for MW excitation.
• Investigated NV center behavior as a function of MW power and field inhomogeneity.
• Developed a pulse sequence to eliminate MW broadening.

Main Results:

• Achieved a homogeneous MW field region of 42 mm³ with diamond diameters up to 5.2 mm.
• Optimized optically detected magnetic resonance (ODMR) signal contrast and voltage fluctuation.
• Reached a magnetic field sensitivity of 5 nT/√Hz.
• Improved sensitivity by approximately one order of magnitude using extended π-pulse duration.

Conclusions:

• The designed antenna structure enables sensitive NV center-based magnetic field detection.
• Pulse sequence optimization significantly enhances sensitivity by mitigating MW broadening.
• This work provides a pathway for developing highly sensitive spin-based sensors.