Photonic Links for Spin-Based Quantum Sensors

TL;DR

The paper tackles the microwave-delivery bottleneck in spin-based quantum sensing by introducing RF-over-Fiber (RFoF) control of NV center ODMR. Using an electro-optic modulator on a $1310~\mathrm{nm}$ carrier, the authors transmit microwave signals over fiber and recover them with a photodiode near the NV sample, achieving an optical-to-RF efficiency of $\eta_{O\rightarrow RF}=1.81\%$ at $2.90~\mathrm{GHz}$ with $P_{RF,out}= -0.7~\mathrm{dBm}$. RFoF spectra reproduce the NV ODMR response across magnetic fields from $8$ to $36~\mathrm{G}$, delivering $0.6-0.9\%$ contrast at $P_{RF,out}=-5.5~\mathrm{dBm}$ and $>2.2\%$ contrast at $-0.7~\mathrm{dBm}$, demonstrating faithful control with substantially reduced RF power. This approach offers electrical isolation and cryogenic compatibility, providing a scalable route to high-field, low-noise, networked quantum sensing and memory architectures, potentially extending to the $\sim100~\mathrm{GHz}$ regime with improvements in modulation depth and photodiode performance.

Abstract

A growing variety of optically accessible spin qubits have emerged in recent years as key components for quantum sensors, qubits, and quantum memories. However, the scalability of conventional spin-based quantum architectures remains limited by direct microwave delivery, which introduces thermal noise, electromagnetic cross-talk, and design constraints for cryogenic, high-field, and distributed systems. In this work, we present a unified framework for RF-over-fiber (RFoF) control of optically accessible spins through RFoF optically detected magnetic resonance (ODMR) spectroscopy of nitrogen-vacancy (NV) centers in diamond. The RFoF platform relies on an electro-optically modulated telecom-band laser that transmits microwave signals over fiber and a high-speed photodiode that recovers the RF waveform to drive NV center spin transitions. We obtain an RFoF efficiency of 1.81\% at 2.90~GHz, corresponding to $P_{\mathrm{RF,out}}=-0.7$~dBm. The RFoF architecture provides a path toward low-noise, thermally isolated, and cryo-compatible ODMR systems bridging conventional spin-based quantum sensing protocols with emerging distributed quantum technologies.

Figures (3)

• Figure 1: Overview of NV-center ODMR physics and the experimental architectures used in this work. (a) Simplified energy-level diagram of the negatively charged NV center, illustrating optical spin polarization under 532 nm excitation, spin-dependent fluorescence near 637 nm, and shelving through intermediate singlet states that enables ODMR contrast; the ground-state spin transition is split by $D\approx 2.87$ GHz at zero field. (b) Experimental architectures used in this work: (i) RFoF microwave delivery chain in which a 1310 nm laser is electro-optically modulated by an RF source (with optional amplification), transmitted over fiber, and converted back to an electrical microwave tone by a high-speed photodiode biased via a bias-tee/SMU before driving the antenna near the NV sample; (ii) conventional free-space ODMR configuration used as a baseline, including optical excitation/collection optics, a microwave antenna adjacent to the diamond, and an external magnet to apply a controllable field.
• Figure 2: Power dependent ODMR spectra for ensemble NV centers in diamond using the conventional coax-fed antenna. ODMR spectra were measured at increasing RF power levels (0, 3, 9, 15, 21, and 25 dBm) delivered to the antenna feedpoint, with normalized photoluminescence plotted versus microwave frequency. Increasing RF power increases the ODMR contrast and produces modest linewidth broadening consistent with stronger driving. Optical settings were held constant during the sweep.
• Figure 3: RFoF ODMR spectra obtained using the recovered microwave tone from the photodiode to drive the NV ensemble through the same broadband antenna used in the coaxial baseline. (a) Stacked RFoF-driven ODMR spectra near the zero-field splitting ($\sim$2.87 GHz) for varying magnetic fields of 8--36 G, measured at $P_{\mathrm{RF,out}}=-5.5$ dBm delivered to the antenna; the resonance splitting increases with field in agreement with the Zeeman effect and the observed contrast is 0.6--0.9%. (b) RFoF-driven ODMR at a fixed magnetic field comparing two recovered RF powers, showing enhanced contrast at higher delivered power; at $P_{\mathrm{RF,out}}=-0.7$ dBm (2.90 GHz) the contrast exceeds 2.2%, while the lower-power condition reproduces the characteristic ODMR spectrum near 2.87 GHz.