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Highly Localized Delivery of Microwaves to Quantum Bits with a Scanning Loop Micro-Antenna

Sangjun Noh, Minghao Jiang, Javier N. Ramos-Silva, Philip Hemmer, Kamel Haddadi, Peter John Burke

Published Jun 1, 2026• 0 citations
Publisher

Abstract

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.

DOI
10.1109/imsrfsa70221.2026.11624215

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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.
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.
Individual nitrogen vacancy (NV) color centers in diamond are versatile, spin-based quantum sensors. Coherently controlling the spin of NV centers using microwaves in a typical frequency range between 2.5 and 3.5 GHz is necessary for sensing applications. In this work, we present a stripline-based, planar, Ω-shaped microwave antenna that enables one to reliably manipulate NV spins. We found an optimal antenna design using finite integral simulations. We fabricated our antennas on low-cost, transparent glass substrate. We created highly uniform microwave fields in areas of roughly 400 × 400 μm2 while realizing high Rabi frequencies of up to 10 MHz in an ensemble of NV centers.
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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.
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Wide-field nitrogen-vacancy (NV) magnetic imaging at cryogenic temperatures requires microwave excitation and reliable knowledge of the temperature near the sensing region. Here, we report an integrated diamond quantum-sensing platform combining an ensemble of NV centers with a boron-doped diamond (BDD) microwave antenna and thermometer formed on the same diamond substrate. The BDD antenna provides microwave excitation for optically detected magnetic resonance measurements, and the BDD thermometer monitors the thermal environment near the NV sensing region. The BDD thermometer detected laser-induced local heating that was not clearly resolved by a stage-mounted thermometer. Using this platform, we imaged the temperature-dependent Meissner response of multiple cuprate superconductors while recording the temperature. These results demonstrate that the integrated BDD--NV platform provides a practical approach for cryogenic wide-field magnetic imaging with integrated microwave delivery and local thermometry.