Spin-based quantum sensors have been applied to the quantum sensing of magnetic fields from DC to GHz with various schemes. The recently developed quantum spectrum analyzer (QSA) technique based on the nitrogen-vacancy (NV) centers in diamond shows an ultrawide frequency bandwidth in this application. Here, we improve this technique and develop a robust QSA via diamond engineering. This QSA exploits the electron spin resonance of NV centers in an engineered {111} industrial diamond, which cancels the complex process of magnetic arrangement and significantly enhances the robustness of QSA against spin mixing under high magnetic fields in practice. A tunable frequency bandwidth of up to 18 GHz with a maximum instantaneous bandwidth of 2 GHz is achieved as well as a frequency resolution of several MHz and a large dynamic range of 65 dB. Using this QSA, we realize the optical imaging of frequency-modulated microwaves. Our work provides a promising rapid-deployment architecture for QSA and extends its application to spectral analysis in modern communications.
Spin-based quantum sensors have been applied to the quantum sensing of magnetic fields from DC to GHz with various schemes. The recently developed quantum spectrum analyzer (QSA) technique based on the nitrogen-vacancy (NV) centers in diamond shows an ultrawide frequency bandwidth in this application. Here, we improve this technique and develop a robust QSA via diamond engineering. This QSA exploits the electron spin resonance of NV centers in an engineered {111} industrial diamond, which cancels the complex process of magnetic arrangement and significantly enhances the robustness of QSA against spin mixing under high magnetic fields in practice. A tunable frequency bandwidth of up to 18 GHz with a maximum instantaneous bandwidth of 2 GHz is achieved as well as a frequency resolution of several MHz and a large dynamic range of 65 dB. Using this QSA, we realize the optical imaging of frequency-modulated microwaves. Our work provides a promising rapid-deployment architecture for QSA and extends its application to spectral analysis in modern communications.
Microwave (MW) magnetometry utilizing nitrogen-vacancy (NV) centers in diamond offers a broad, tunable detection bandwidth enabled by the magnetic-field-dependent electron spin resonances (ESR) of the NV centers. In this work, we present and experimentally demonstrate two NV-based protocols for spectral analysis of amplitude-modulated (MW) signals. The first protocol employs the NV center as a bandpass filter and reconstructs frequency-domain information of MW signals by sweeping the MW carrier frequency. The second protocol achieves optical imaging of the MW spectrum using an NV-based quantum spectrum analyzer, wherein a magnetic field gradient spatially maps the ESR frequencies of the NV centers, enabling parallel detection of multiple spectral components over a wide instantaneous bandwidth. Both protocols show results that agree well with reference measurements from a classical spectrum analyzer. Our approaches extend the application of spin-based quantum sensors to the field of modern communications and can be adapted for other spin-based quantum sensors.
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.
Abstract The rapid development of radio-frequency (RF) technologies requires tools which can efficiently monitor the electromagnetic landscape. Broadband real-time RF spectral analyzers need to operate at room temperature, with low power consumption and have a compact design for on-board device integration. Here we describe a Quantum Diamond Signal Analyzer (Q-DiSA) which detects RF signals over a tunable frequency range of 25 GHz with frequency resolution down to 1 MHz, a millisecond temporal resolution and a large dynamic range (40 dB). This approach exploits the room temperature spin properties of an ensemble of nitrogen-vacancy (NV) centers in diamond. Performance is enabled via our analyzer architecture which combines a specific diamond crystallographic cut with a simplified magnetic arrangement. This allows us to maintain the alignment of the magnetic field along the nitrogen-vacancy center axis whilst frequency tuning. These results demonstrate the potential of the Q-DiSA method for real-time broadband spectral analysis.
Developing high performance portable sensors is of significant importance for both terrestrial and satellite communications, with quantum sensors offering potential advantages in sensitivity and bandwidth. The nitrogen vacancy center in diamond is a popular quantum sensing platform for its relative simplicity and wide range of acceptable operating conditions, but suffers a limited instantaneous bandwidth due to the narrow linewidth of the spin resonance. In this work, we first present a magnetic quantum sensing scheme utilizing heterodyne mixing with strong optical and microwave driving, achieving MHz-scale instantaneous bandwidth with a sensitivity of 548pT/Hz in an active diamond volume of $ 2.5\times 10^{-4} \; \text{mm}^3$ with 2×1011 NV centers. We then demonstrate expansion of the sensing bandwidth by employing a strong magnetic gradient and many individually modulated microwave control fields, expanding the single resonance bandwidth to 48 MHz with a peak sensitivity of 8.5nT/Hz.
We propose an original analog method to perform instantaneous and quantitative spectral analysis of microwave signals. An ensemble of nitrogen-vacancy (NV) centers held in a diamond plate is pumped by a 532 nm laser. Its photoluminescence is imaged through an optical microscope and monitored by a digital camera. An incoming microwave signal is converted into a microwave field in the area of the NV centers by a loop shaped antenna. The resonances induced by the magnetic component of that field are detected through a decrease of the NV centers photoluminescence. A magnetic field gradient induces a Zeeman shift of the resonances and transforms the frequency information into spatial information, which allows for the simultaneous analysis of the microwave signal in the entire frequency bandwidth of the device. The time dependent spectral analysis of an amplitude modulated microwave signal is demonstrated over a bandwidth of 600 MHz, associated to a frequency resolution of 7 MHz , and a refresh rate of 4 ms. With such integration time, a field of a few hundreds of μW can be detected. Since the optical properties of NV centers can be maintained even in high magnetic field, we estimate that an optimized device could allow frequency analysis in a range of 30 GHz, only limited by the amplitude of the magnetic field gradient. In addition, an increase of the NV centers quantity could lead both to an increase of the microwave sensitivity and to a decrease of the minimum refresh rate down to a few μs.
The nitrogen-vacancy (NV) center in diamond has attracted considerable attention as a highly sensitive quantum sensor that can operate at room temperature. In particular, continuous-wave optically detected magnetic resonance (CW-ODMR) is promising for a wide range of applications because of its simplicity. However, conventional AC magnetic-field sensing schemes based on CW-ODMR suffer from a limited detection bandwidth: the detectable frequency is either fixed by intrinsic physical parameters of the NV center or, even when tunable, restricted to a narrow range of only a few MHz. Here, we propose a broadband AC magnetometry scheme based on CW-ODMR with NV centers using microwave-driven dressed states.Through theoretical analysis and numerical simulations, we show that the proposed scheme enables the detection of AC magnetic fields with frequencies up to the order of 100 MHz, which has been difficult to achieve using conventional CW-ODMR-based methods.