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Photonics for Quantum (PfQ)

Microwave-induced fluorescence of ensemble NV centers using PCB-based RF devices for quantum sensing

Atefe Safinezhad, Aashutosh Kumar, Richard Al Hadi, Bora Ung

Published Jul 22, 2026• 0 citations
Publisher

Abstract

Nitrogen-vacancy (NV) centers in diamond are solid-state quantum sensors that operate at room temperature and allow optical readout of spin states through optically detected magnetic resonance (ODMR). Reliable ODMR measurements need controlled microwave excitation to manipulate NV spin states and modulate their fluorescence. In this paper, we report on ensemble NV centers’ interaction with microwave fields transmitted by printed-circuit-board (PCB) radio-frequency (RF) devices. Two microwave structures, a coplanar waveguide transmission line (CPW-TL) and a single-finger interdigitated capacitor (IDC), are designed and impedance-matched at the NV zero-field splitting frequency. Nanodiamond solutions containing NV ensembles are deposited as few-microliter droplets onto the PCB devices and dried, forming localized NV layers on the RF structures. Two-dimensional fluorescence scans are used to link spatial changes in NV fluorescence to the microwave field distributions created by each device geometry. CPW-TLs enable interaction over extended regions along the transmission line, while IDCs produce localized excitation near the capacitive gaps.

DOI
10.1117/12.3111912

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Nitrogen-vacancy (NV) centers in diamond are solid-state quantum sensors that operate at room temperature and allow optical readout of spin states through optically detected magnetic resonance (ODMR). Reliable ODMR measurements need controlled microwave excitation to manipulate NV spin states and modulate their fluorescence. In this paper, we report on ensemble NV centers’ interaction with microwave fields transmitted by printed-circuit-board (PCB) radio-frequency (RF) devices. Two microwave structures, a coplanar waveguide transmission line (CPW-TL) and a single-finger interdigitated capacitor (IDC), are designed and impedance-matched at the NV zero-field splitting frequency. Nanodiamond solutions containing NV ensembles are deposited as few-microliter droplets onto the PCB devices and dried, forming localized NV layers on the RF structures. Two-dimensional fluorescence scans are used to link spatial changes in NV fluorescence to the microwave field distributions created by each device geometry. CPW-TLs enable interaction over extended regions along the transmission line, while IDCs produce localized excitation near the capacitive gaps.
The Nitrogen-Vacancy (NV) center in diamond is a prominent quantum system leveraged for advanced quantum metrology, particularly in high-precision magnetometry and high-resolution quantum imaging, exploiting the Optically Detected Magnetic Resonance (ODMR) spectroscopy technique. Proper radio-frequency (RF) excitation of NV centers is critical in order to manipulate these quantum states effectively. Our research focuses on optimizing the continuous-wave RF excitation of ensembles of NV centers on coplanar waveguide transmission lines (CPW-TL), measuring the centers' photoluminescence (PL) signal as a function of RF power. This setup enhances the sensitivity and resolution of the NV center PL signal. By combining CPW-TL lines with nanodiamonds, our approach aims to develop a scalable and tunable platform that can be deployed in a variety of quantum sensing scenarios, including in biomedical applications, navigation systems, environmental monitorlng, and beyond.
We demonstrate highly localized delivery of microwaves to quantum bits with a scanning loop micro-antenna. The quantum state of the qubits (ensembles of nitrogen vacancy centers in microdiamond) is read out optically, via optically detected magnetic resonance (ODMR). A 600 × 600 μm2 via-based PCB loop antenna is specifically designed as efficient microwave excitation source. A piezo micromanipulator from Sensapex™ provides precise control of the antenna position above microdiamond containing nitrogen-vacancy (NV) centers, enabling spatially resolved ODMR measurements. 1D line and 2D imaging scans reveal the local microwave near-field distribution generated by the loop antenna. These results demonstrate spatially resolved ODMR mapping using a custom-built free-space optical configuration and establish a basis for future NV-based quantum sensing and microwave field characterization, as well as laying the foundation for quantum state manipulation of individual qubits using programmable, highly localized delivery of microwaves.
Abstract Multiple-microwave-photon transition is a nonlinear process involving the simultaneous absorption of multiple microwave photons to reach a higher energy state. This phenomenon enables microwave frequency conversion, a crucial technique for spin-wave devices, frequency synthesizers and communication devices. However, it has not been observed in nitrogen-vacancy (NV) centers in diamonds, which serve as a key quantum platform linking flying qubits, microwave photons, and solid-state spins. In this work, we first observed multiple-microwave-photon transitions in NV centers in diamonds, using optically detected magnetic resonance (ODMR) methods with a single laser and microwave beam. We demonstrate that microwave frequencies, effective g-factor, and angular momentum exhibit a 1/n scaling law, but the linewidth exhibits a 1/n^2 scaling law for n-photon transitions between the ground states. Additionally, we detect the hyperfine structure of the ground states and achieve coherent spin manipulation under multi-photon excitation. Our findings offer a novel approach for the precise manipulation of NV center spin states, advancing quantum sensing and quantum information.
For quantum sensing based on nitrogen-vacancies (NV) ensembles, microwave antennas can couple the microwave field to the NV center, which leads it to becoming the core of spin manipulation and can directly affect the sensitivity of quantum sensing. The double split-ring resonator is a widely used microwave device for NV ensembles due to the advantages of high radiation efficiency and uniform magnetic field in millimeter-scale areas. But the bandwidth (30 MHz) is quite narrow which limits the application in quantum sensing with NV ensembles. Here, we experimentally achieve continuous tuning of the resonant frequency of the double split-ring resonator by changing the copper sheet position on the edge of the outer ring. The frequency tuning range can reach 80 MHz, up to 2-3 times the bandwidth, which can cover the transition of the electron spin under different magnetic field conditions. The performance of the tunable antenna in the quantum operation of NV centers is verified by optically detected magnetic resonance and Rabi oscillation. This tunable antenna is promising in the fabrication of integrated and arrayed quantum sensors based on NV ensembles.
In this work, we designed, simulated, and tested a complementary split ring resonator (CSRR) for the purpose of applying a strong and uniform microwave field for the manipulation of nitrogen vacancy (NV) ensembles. This structure was fabricated by etching two concentric rings on a flat metal film that was deposited on a printed circuit board. A metal transmission on the back plane was used as the feed line. The fluorescence collection efficiency was improved by about 2.5 times with the CSRR structure compared to that without CSRR. Furthermore, the maximum Rabi frequency could reach 11.3 MHz, and the Rabi frequency variation was smaller than 2.8% in an area of 250 × 75 μm. This could pave the way to achieving high-efficiency control of the quantum state for spin-based sensor applications.
Nitrogen-Vacancy (NV) centers in diamond are attractive tools for sensing and quantum information. Realization of this potential requires effective tools for controlling the spin degree of freedom by microwave (mw) magnetic fields. In this work, we present a planar microwave resonator optimized for microwave-optical double resonance experiments on single NV centers in diamond. It consists of a piece of wide microstrip line, which is symmetrically connected to two 50 Ω microstrip feed lines. In the center of the resonator, an Ω-shaped loop focuses the current and the mw magnetic field. It generates a relatively homogeneous magnetic field over a volume of 0.07 × 0.1 mm3. It can be operated at 2.9 GHz in both transmission and reflection modes with bandwidths of 1000 and 400 MHz, respectively. The high power-to-magnetic field conversion efficiency allows us to produce π-pulses with a duration of 50 ns with only about 200 and 50 mW microwave power in transmission and reflection, respectively. The transmission mode also offers capability for efficient radio frequency excitation. The resonance frequency can be tuned between 1.3 and 6 GHz by adjusting the length of the resonator. This will be useful for experiments on NV-centers at higher external magnetic fields and on different types of optically active spin centers.