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Physical Review X

Sensing of Arbitrary-Frequency Fields Using a Quantum Mixer

Guoqing Wang, Yi-Xiang Liu, Jennifer M. Schloss, Scott T. Alsid, Danielle Braje, Paola Cappellaro

Published Jun 17, 2022• 71 citations
Publisher

Abstract

Quantum sensors such as spin defects in diamond have achieved excellent performance by combining high sensitivity with spatial resolution.Unfortunately, these sensors can only detect signal fields with frequency in a few accessible ranges, typically low frequencies up to the experimentally achievable control field amplitudes and a narrow window around the sensors' resonance frequency.Here, we develop and demonstrate a technique for sensing arbitrary-frequency signals by using the sensor qubit as a quantum frequency mixer, enabling a variety of sensing applications.The technique leverages nonlinear effects in periodically driven (Floquet) quantum systems to achieve quantum frequency mixing of the signal and an applied bias ac field.The frequency-mixed field can be detected using well-developed sensing techniques such as Rabi and CPMG with the only additional requirement of the bias field.We further show that the frequency mixing can distinguish vectorial components of an oscillating signal field, thus enabling arbitrary-frequency vector magnetometry.We experimentally demonstrate this protocol with nitrogenvacancy centers in diamond to sense a 150-MHz signal field, proving the versatility of the quantum mixer sensing technique.

DOI
10.1103/physrevx.12.021061

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Quantum sensors such as spin defects in diamond have achieved excellent performance by combining high sensitivity with spatial resolution.Unfortunately, these sensors can only detect signal fields with frequency in a few accessible ranges, typically low frequencies up to the experimentally achievable control field amplitudes and a narrow window around the sensors' resonance frequency.Here, we develop and demonstrate a technique for sensing arbitrary-frequency signals by using the sensor qubit as a quantum frequency mixer, enabling a variety of sensing applications.The technique leverages nonlinear effects in periodically driven (Floquet) quantum systems to achieve quantum frequency mixing of the signal and an applied bias ac field.The frequency-mixed field can be detected using well-developed sensing techniques such as Rabi and CPMG with the only additional requirement of the bias field.We further show that the frequency mixing can distinguish vectorial components of an oscillating signal field, thus enabling arbitrary-frequency vector magnetometry.We experimentally demonstrate this protocol with nitrogenvacancy centers in diamond to sense a 150-MHz signal field, proving the versatility of the quantum mixer sensing technique.
Achieving high-frequency spectral resolution with quantum sensors, while crucial in fields ranging from physical to biological sciences, is challenging due to their finite coherence time. Here, we introduce a novel protocol that achieves this goal by measuring phase correlations of AC magnetic fields using ensembles of NV centers. Our method extends the sensing dynamic range to frequencies higher than the system's Rabi frequency while achieving arbitrary frequency resolution, limited only by the target field coherence time. Moreover, our approach operates more robustly with respect to the magnetic field's amplitude. Thanks to this robustness, our protocol allows the application of more πππ-pulses in pulse sequences such as CPMG, enabling the decoupling of a broader range of frequency noise. The higher harmonics generated in this process continue to act as a part of the signal, ultimately improving the frequency resolution. This method paves the way for achieving arbitrary frequency resolution with improved performances, making it highly versatile for quantum sensing applications across diverse scientific fields.
Quantum sensors are keeping the cutting-edge sensitivities in metrology. However, for high-sensitive measurements of arbitrary signals, limitations in linear dynamic range could introduce distortions when sensing the frequency, magnitude and phase of unknown signals. Here, we overcome these limitations with advanced sensing protocol that combines quantum phase-sensitive detection with heterodyne readout. We present theoretical and experimental investigations using nitrogen-vacancy centers in diamond, showing the ability to sense radio signals with a 98 dB linear dynamic range, a 31 pT/Hz1/2^{1/2}1/2 sensitivity, and arbitrary frequency resolution. Further, we use the sensor as a quantum radio receiver to show the capability in detecting audio signals (melody piece, speech) with high fidelity. The methods developed here could broaden the horizon for quantum sensors towards applications in telecommunication, where high-fidelity and low-distortion at multiple frequency bands within small sensing volumes are required.
Magnetic field fluctuations on nanometer length scales manifest in a diverse range of phenomena -- electron and spin dynamics in materials and devices, quantum many-body systems, and molecular chemistry. Measuring these phenomena requires sensors with a challenging combination of broad spectral bandwidth, high sensitivity, and nanoscale spatial resolution. Nitrogen-vacancy (NV) centers, atom-like quantum sensors in diamond, possess the requisite sensitivity and nanoscale sensing volume, but are typically limited in bandwidth by the practical speed of the applied quantum control sequence. Here, we overcome this limitation by exposing the NV qubit to a microwave dressing field during a dynamical decoupling sequence, which both amplifies and frequency-mixes target signals at arbitrary frequencies into the detection band of the dynamical decoupling protocol. We demonstrate this approach by using NV centers to detect both coherent and noisy nanoscale spin wave dynamics in a magnetic yttrium-iron-garnet (YIG) thin film over a broad frequency range. Our technique generalizes to other qubit platforms, providing a versatile framework for nanoscale spectroscopy across diverse physical and chemical systems.
Abstract Quantum sensors are keeping the cutting-edge sensitivities in metrology. However, for high-sensitive measurements of arbitrary signals, limitations in linear dynamic range could introduce distortions when sensing the frequency, magnitude and phase of unknown signals. Here, we overcome these limitations with advanced sensing protocol that combines quantum phase-sensitive detection with the heterodyne readout. We present theoretical and experimental investigations using nitrogen-vacancy centers in diamond, showing the ability to sense audio signals with a 98 dB linear dynamic range, a 31 pT/Hz1/2 sensitivity, and arbitrary frequency resolution. Further, we perform the quantum-assisted distortion-free audio signal (melody, speech) sensing with high fidelity. The methods developed here could broaden the horizon for quantum sensors towards applications in telecommunication, where high-fidelity and low-distortion at multiple frequency bands within small sensing volumes are required.
Quantum sensors are known for their high sensitivity in sensing applications. However, this sensitivity often comes with severe restrictions on other parameters which are also important. Examples are that in measurements of arbitrary signals, limitation in linear dynamic range could introduce distortions in magnitude and phase of the signal. High frequency resolution is another important feature for reconstructing unknown signals. Here, we demonstrate a distortion-free quantum sensing protocol that combines a quantum phase-sensitive detection with heterodyne readout. We present theoretical and experimental investigations using nitrogen-vacancy centers in diamond, showing the capability of reconstructing audio frequency signals with an extended linear dynamic range and high frequency resolution. Melody and speech based signals are used for demonstrating the features. The methods could broaden the horizon for quantum sensors towards applications, e.g. telecommunication in challenging environment, where low-distortion measurements are required at multiple frequency bands within a limited volume.
The diamond sensor has emerged as a promising platform for quantum sensing, enabling the estimation of physical quantities -- such as microwave~(MW) field -- with precision unattainable by classical counterpart. However, traditional diamond sensors suffer severe precision degradation when the signal MW is not resonant with the sensor transition frequency. Here, we propose and demonstrate a Floquet diamond sensor~(FDS) for high-precision off-resonant MW amplitude sensing without attenuating the strength of the signal MW. The periodic driven field effectively induces an quasi-energy shift that matches the off-resonant MW frequency. The measurement precision of FDS is characterized by quantum Fisher information, which approaches the ultimate precision -- Heisenberg limit -- within the coherent time. Furthermore, the FDS exhibits robust tolerance to practical control errors and is compatible with dynamical coupling protocol, enabling a robust and high-sensitivity magnetic sensing. Our results confirm the quantum advantage of quantum sensing and provide a practical technology for high-precision off-resonant MW sensing.