Diamond nitrogen-vacancy center is a widely studied platform for high frequency magnetometry. However, efficient field generator in a broadband field up to millimeter wave is still an open issue. In this work, we present a high-performance microwave magnetic field generator by incorporating gradient signal line coplanar waveguide design, achieving efficient generation of microwave magnetic field over an ultrawide band with a fairly good impedance match. This device uses standard PCB process and ensures efficient microwave excitation in an ultrabroad band up to 50 GHz for NV center experiments, promoting metrology applications for strong magnetic field and high-frequency.
Diamond nitrogen-vacancy center is a widely studied platform for high frequency magnetometry. However, efficient field generator in a broadband field up to millimeter wave is still an open issue. In this work, we present a high-performance microwave magnetic field generator by incorporating gradient signal line coplanar waveguide design, achieving efficient generation of microwave magnetic field over an ultrawide band with a fairly good impedance match. This device uses standard PCB process and ensures efficient microwave excitation in an ultrabroad band up to 50 GHz for NV center experiments, promoting metrology applications for strong magnetic field and high-frequency.
We report on coplanar waveguides (CPWs) designed for optically detected magnetic resonance of nitrogen-vacancy (NV) centers in diamonds. A broad band up to 15.8 GHz has been realized, which ensures that the electron spins can be manipulated under external magnetic fields up to 5000 G. The conversion factor of CPW has been measured by Rabi nutation experiments, which ranges from 6.64 G W−1/2 to 10.60 G W−1/2 in the frequency band from 0.76 GHz to 17.3 GHz. Broadband CPWs also provide high quality control pulses due to the minimization of the distortion. These characteristics will find potential applications in NV-based quantum information processing and single spin magnetometry.
The nitrogen-vacancy (NV) color center in diamond has found applications in magnetometry across various geometrical scales. In particular, vector magnetometry using hand-held devices with low power consumption is of interest for mobile and geological applications. However, such a device requires efficient driving of the four different orientations of the NV center, thus placing demands on a broadband microwave resonator that provides a uniform and highly insensitive microwave magnetic field at the resonance frequencies of the NV centers. Here, we propose a unique planar resonator design that enables efficient driving of all four orientations of NV color centers over a 100 MHz range with only 0.5 W of microwave input power and 250 mW of laser power, allowing vector magnetic field measurements. Using the planar resonator to drive NV centers in diamond, a compact vector magnetometer was fabricated and experimentally studied. The sensitivity of the device is about 1.2 nT/Hz. While this is not a record sensitivity for diamond-based magnetometers, this device occupies its own niche as a compact hand-held magnetometer.
We present a wideband balun-based microwave device for quantum manipulation of nitrogen-vacancy centers in diamond. The device employs a balun with multi-section Chebyshev impedance transformer to realize the conversion from the unbalanced feed line to the balanced feed line and ensures impedance matching. A bandwidth of 2.2 GHz with the maximum resonance frequency up to 4.4 GHz has been realized, which is important for multi-qubit quantum control of the nitrogen-vacancy centers. We also carry out optically detected magnetic resonance to observe Rabi oscillations and calibrate the strength of the microwave magnetic field generated by the microwave device. With an input power of 0.5 W, the Rabi frequencies can reach 6.17 MHz and 6.06 MHz for resonant microwave at 1.40 GHz and 4.34 GHz, respectively. Combining with large bandwidth and excellent magnetic field homogeneity, the device can be applied in solid-state quantum information processing.
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.
Nitrogen-vacancy (NV) centers in diamond have emerged as promising quantum sensors due to their highly coherent and optically addressable spin states with potential applications in high-sensitivity magnetometry. Homogeneously addressing large ensembles of NV centers offers clear benefit in terms of sensing precision as well as in fundamental studies of collective effects. Such experiments require a spatially uniform, intense, and broadband microwave field that can be difficult to generate. Previous approaches, such as copper wires, loop coils, and planar structures, have shown limitations in field homogeneity, bandwidth, and integration in compact devices. In this paper, we present a coplanar waveguide (CPW) gold coil patterned on a 3 × 3 mm 2 diamond substrate, offering full integration, enhanced stability, and broad bandwidth suitable for various NV sensing applications. Coil fabricated on diamond offers several advantages for magnetometry with NV centers ensemble, including enhanced heat dissipation, seamless integration, scalability, and miniaturization potential. We optimize critical geometrical parameters to achieve a homogeneous magnetic field with a coefficient of variation of less than 6% over an area of 0.5 mm 2 and present experimental results confirming the performance of the proposed CPW coil.
High-resolution wide-spectrum measurement techniques have important applications in fields such as astronomy, wireless communication, and medical imaging. Nitrogen-vacancy (NV) center in diamond is well known for its high stability, high sensitivity, real-time monitoring, single-point detection, and suitability for long-term measurement, and has an outstanding choice for spectrum analyzers. Currently, spectrum analyzers based on NV centers as detectors can perform real-time spectrum analysis in the range of several tens of gigahertz, but their frequency resolution is limited to a MHz level. In this study, we construct a quantum diamond microwave spectrum imaging system by combining continuous wave-mixing techniques. According to the spin-related properties of the NV center in diamond, we implement optical pumping by 532 nm green laser light illuminating the diamond NV center. A spherical magnet is used to produce a magnetic field gradient along the direction of the diamond crystal. By adjusting the size and direction of the magnetic field gradient, spatial encoding of the resonance frequency of the NV center is achieved. The magnetic field gradient induces the Zeeman effect on the diamond surface at different positions, generating corresponding ODMR signals. Through accurate programming, we coordinate the frequency scanning step size of the microwave source with the camera exposure and image storage time, and synchronize them circularly according to the order of image acquisition. Ultimately, after algorithmic processing, we successfully obtain comprehensive spectrum data in a range from 900 MHz to 6.0 GHz. Within the measurable spectrum range, the system employs continuous wave-mixing, simultaneously applying resonant microwaves and slightly detuning auxiliary microwaves to effectively excite the NV center. This method triggers off microwave interference effects, disrupting the balance between laser-induced polarization and microwave-induced spontaneous relaxation. Specifically, microwave interference causes the phase and amplitude of the fluorescence signal to change, leading to the generation of alternating current fluorescence signals. This further enhances the response of the NV magnetometer to weak microwave signals. The method enables the system to achieve a frequency resolution of 1 Hz in the measurable spectrum range, and it can separately measure the frequency resolution of multiple frequency points with a frequency step size of 1 MHz. The research results indicate that the wide-spectrum measurement based on NV centers can achieve sub-hertz frequency resolution, providing robust technical support for future spectrum analysis and applications.