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.
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.
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.
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.
The nitrogen-vacancy center (NV) is a diamond spin defect consisting of a nitrogen atom and a carbon vacancy in two adjacent positions of the diamond lattice. Its remarkable spin-dependent optical properties make it a promising platform for quantum sensing and quantum information applications.In the present manuscript, two applications involving an ensemble of NV centers in diamond are investigated: a radio frequency (RF) spectrum analyser and a widefield imaging technique of the RF radiation emitted in near field by microwave devices.In the first chapter, the NV centers in diamond, their properties and the motivations behind the two NV centers based applications proposed in this manuscript are presented. The available solutions and the state-of-the-art techniques for both RF spectral analysis and near field imaging of RF radiation are reviewed and the potential of alternative solutions using NV centres are discussed.In the second chapter, a set-up for the widefield optical detection of the NV centers spin resonances is presented and used to investigate the main properties of this diamond defect. The NV center electron spin resonances are detected over a large frequency range (more than 10 GHz) and different phenomena are investigated: the behaviour of an ensemble of NV centers under a static magnetic field, the polarization properties of the NV center photoluminescence (PL) and how they can be exploited to recognise the NV centers orientations, the NV’s nitrogen nuclear spin polarization over a large frequency range (more than 2 GHz).The third chapter is devoted to the implementation of a real-time RF spectrum analyser based on an ensemble of NV centers. The main physical features of NV centers considered as MW detectors are investigated and an experimental architecture which allows a real time RF spectral analysis over a tuneable frequency range (10 MHz to 25 GHz), 4 GHz bandwidth, a MHz frequency resolution and a ms time resolution is demonstrated. The implementation of this device required an interesting analysis on the behaviour of an ensemble of NV centers under strong magnetic field gradient (tens of Tesla per meter) which is detailed in the chapter.The fourth and last chapter deals with the widefield imaging of RF field based on an ensemble of NV centers. Two techniques are proposed. The first is based on the RF power broadening of the NV center spin resonances in the continuous regime domain while the second is based on the widefield detection of NV centers Rabi oscillations in a pulsed regime. Both techniques allowed reconstructing the magnetic near field RF field emitted by a loop antenna. However, while the first technique requires a calibration to retrieve the amplitude of the RF field, the second allows a direct measurement of it. The widefield detection of the NV centers Rabi oscillations has thus been investigated both by means of experiments and simulations. Since the NV centers Rabi oscillations detected using our widefield experimental set-up showed an asymmetric shape, a model has been realized to figure out the NV centers behaviour during the pulse sequence employed to drive the Rabi oscillation. The results of the simulations, in agreement with the experimental results, enable to have a better insight of the NV center spin optical polarization and readout during the widefield detection of the Rabi oscillations.
We have realized a compact radiofrequency spectrum analyzer based on nitrogen-vacancy (NV) color centers in diamond. The RF spectral components are spatially encoded by means of a Zeeman shift of the NV resonances induced by a magnetic field gradient. The fluorescence of the NV centers is imaged on a CMOS detector array using a gradient index lens. The spectral components of the signal are revealed by the appearance of dark lines in the image. We observed frequencies up to 10 GHz, with a resolution of a few MHz and a RF sensitivity of the order of 100 µW.
Abstract Quantum systems composed of solid-state electronic spins can be sensitive detectors of narrowband magnetic fields. A prominent example is the nitrogen-vacancy (NV) center in diamond, which has been employed for magnetic spectroscopy with high spatial and spectral resolution. However, NV-diamond spectroscopy protocols are typically based on dynamical decoupling sequences, which are limited to low-frequency signals (≲ 20 MHz) due to the technical requirements on microwave (MW) pulses used to manipulate NV electronic spins. In this work, we experimentally demonstrate a high-resolution magnetic spectroscopy protocol that integrates a quantum frequency mixing (QFM) effect in a dense NV ensemble with coherently averaged synchronized readout (CASR) to provide both a wide range of signal frequency detection and sub-Hz spectral resolution. We assess the sensitivity of this QFM-CASR protocol across a frequency range of 10 MHz to 4 GHz. By measuring the spectra of multi-frequency signals near 0.6, 2.4 and 4 GHz, we demonstrate sub-Hz spectral resolution with a nT-scale noise floor for the target signal, and precise phase measurement with error <1°. Compared to state-of-the-art NV-diamond techniques for narrowband magnetic spectroscopy, the QFM-CASR protocol greatly extends the detectable frequency range, enabling applications in high-frequency radio frequency (RF) and MW signal microscopy and analysis, as well as tesla-scale nuclear magnetic resonance (NMR) spectroscopy of small samples.
Quantum systems composed of solid-state electronic spins can be sensitive detectors of narrowband magnetic fields. A prominent example is the nitrogen-vacancy (NV) center in diamond, which has been employed for magnetic spectroscopy with high spatial and spectral resolution. However, NV-diamond spectroscopy protocols are typically based on dynamical decoupling sequences, which are limited to low-frequency signals ( ≲ 20 MHz) due to the technical requirements on microwave (MW) pulses used to manipulate NV electronic spins. In this work, we experimentally demonstrate a high-resolution magnetic spectroscopy protocol that integrates a quantum frequency mixing (QFM) effect in a dense NV ensemble with coherently averaged synchronized readout (CASR) to provide both a wide range of signal frequency detection and sub-Hz spectral resolution. We assess the sensitivity of this QFM-CASR protocol across a frequency range of 10 MHz to 4 GHz. By measuring the spectra of multi-frequency signals near 0.6, 2.4 and 4 GHz, we demonstrate sub-Hz spectral resolution with a nT-scale noise floor for the target signal, and precise phase measurement with error < 1 ∘ . Compared to state-of-the-art NV-diamond techniques for high-resolution magnetic spectroscopy, the QFM-CASR protocol extends the signal frequency range by more than an order of magnitude, enabling applications in radio frequency (RF) and MW signal microscopy and analysis, as well as tesla-scale nuclear magnetic resonance (NMR) spectroscopy of small samples.