Broadband loop gap resonator for nitrogen vacancy centers in diamond

Area of Science:

• Quantum sensing
• Materials science
• Microwave engineering

Background:

• Nitrogen-vacancy (NV) ensembles are crucial for quantum sensing and imaging.
• Achieving homogeneous and strong microwave (MW) fields is essential for driving NV ensembles effectively.
• Existing methods often lack the required field uniformity, bandwidth, or optical access for advanced applications.

Purpose of the Study:

• To present a novel S-band tunable loop gap resonator (LGR) for enhanced microwave (MW) control of nitrogen-vacancy (NV) ensembles.
• To characterize the performance of the LGR in terms of field strength, homogeneity, and bandwidth.
• To demonstrate versatile coupling methods for integration into sensing and imaging systems.

Main Methods:

• Fabrication of an S-band tunable loop gap resonator (LGR).
• Characterization of microwave (MW) drive field amplitude, homogeneity, and bandwidth using established measurement techniques.
• Demonstration of two power coupling methodologies: printed circuit board (PCB) exciter antenna and inductive coupling coil.
• Evaluation of optical access provided by the inductive coupling method.

Main Results:

• The LGR provides strong (approaching 5 G), homogeneous, and directionally uniform broadband MW drive.
• Achieved drive field homogeneity with fractional root-mean-square (rms) inhomogeneity σ_rms = 1.6% over 11 mm² and σ_rms = 3.2% over 32 mm².
• The device exhibits an 80 MHz bandwidth, enabling driving of all NV Zeeman resonances for bias fields below 20 G.
• Demonstrated two coupling methods, with the inductive coil offering ~2π steradian optical access.

Conclusions:

• The developed S-band tunable LGR significantly enhances MW control for NV ensembles.
• The device's performance in terms of field strength, homogeneity, and bandwidth is suitable for advanced quantum sensing and imaging.
• The demonstrated coupling methods offer flexibility for integration into various NV-based systems, facilitating broader adoption in bulk sensing and microscopy.