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arXiv:2510.03618

Floquet Diamond Sensor with Optimal Precision

Qigeng Duan, Teng Li, Siqi Chen, Pang, Shengshi, Lu He

Published Oct 4, 2025• 0 citations
arXivHTMLPDF

Abstract

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.

DOI
10.48550/arxiv.2510.03618

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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.
Diamond quantum sensors are sensitive to weak microwave magnetic fields resonant to the spin transitions. However, the spectral resolution in such protocols is ultimately limited by the sensor lifetime. Here, we demonstrate a heterodyne detection method for microwaves (MW) leading to a lifetime independent spectral resolution in the GHz range. We reference the MW signal to a local oscillator by generating the initial superposition state from a coherent source. Experimentally, we achieve a spectral resolution below 1 Hz for a 4 GHz signal far below the sensor lifetime limit of kilohertz. Furthermore, we show control over the interaction of the MW-field with the two-level system by applying dressing fields, pulsed Mollow absorption and Floquet dynamics under strong longitudinal radio frequency drive. While pulsed Mollow absorption leads to improved sensitivity, the Floquet dynamics allow robust control, independent from the system's resonance frequency. Our work is important for future studies in sensing weak microwave signals in a wide frequency range with high spectral resolution.
Abstract Diamond quantum sensors are sensitive to weak microwave magnetic fields resonant to the spin transitions. However, the spectral resolution in such protocols is ultimately limited by the sensor lifetime. Here, we demonstrate a heterodyne detection method for microwaves (MW) leading to a lifetime independent spectral resolution in the GHz range. We reference the MW signal to a local oscillator by generating the initial superposition state from a coherent source. Experimentally, we achieve a spectral resolution below 1 Hz for a 4 GHz signal far below the sensor lifetime limit of kilohertz. Furthermore, we show control over the interaction of the MW-field with the two-level system by applying dressing fields, pulsed Mollow absorption and Floquet dynamics under strong longitudinal radio frequency drive. While pulsed Mollow absorption leads to improved sensitivity, the Floquet dynamics allow robust control, independent from the system’s resonance frequency. Our work is important for future studies in sensing weak microwave signals in a wide frequency range with high spectral resolution.
The nitrogen-vacancy centers in diamond have exhibited excellent sensing capabilities. By applying the resonance frequency tracking (RFT) method in a closed-loop system, magnetic-field measurements with a wide dynamic range have been demonstrated. However, the previous strategies employ phase-sensitive control signals, which degrade control robustness and reduce tracking rates, thereby impeding real-time measurements. Here, an amplitude–phase joint discrimination strategy is proposed to improve robustness, overcoming the limitations of existing strategies that are sensitive to phase delays in fluorescence signal transmission. Moreover, to improve the tracking speed, a customized device, integrating a fast-response lock-in amplifier (LIA) and a frequency-agile microwave (MW) source, is reported. The LIA achieves a response time as short as 20 μs, while the MW source reaches a frequency switching time of 1 μs. The proposed strategy and customized device are implemented and evaluated on an all-fiber quantum current sensing system. Test results show that the system achieves a maximum sampling rate of 20 kHz, with excellent linearity (a linear deviation of 0.37% over the range of 0-120 A) and high accuracy (a measurement error of 0.73% at 80 A), making it promising for a wide range of high-speed quantum measurement scenarios.
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.
Permitting a more precise measurement to physical quantities than the classical limit by using quantum resources, quantum metrology holds a promise in developing many revolutionary technologies. However, the noise-induced decoherence forces its superiority to disappear, which is called no-go theorem of noisy quantum metrology and constrains its application. We propose a scheme to overcome the no-go theorem by Floquet engineering. It is found that, by applying a periodic driving on the atoms of the Ramsey spectroscopy, the ultimate sensitivity to measure their frequency characterized by quantum Fisher information returns to the ideal t^{2} scaling with the encoding time whenever a Floquet bound state is formed by the system consisting of each driven atom and its local noise. Combining with the optimal control, this mechanism also allows us to retrieve the ideal Heisenberg-limit scaling with the atom number N. Our result gives an efficient way to avoid the no-go theorem of noisy quantum metrology and to realize high-precision measurements.
The nitrogen–vacancy center in diamond enables highly sensitive magnetic-field measurements. In this work, we demonstrate an excellent sensitivity of 7.9 pT·Hz –1/2 in the near-DC range of 1 to 1000 Hz. This performance is achieved using a 35 mW laser power and 1 mW microwave power enabled by 561 nm laser excitation and the resonant-antenna design. By leveraging dual resonance with intrinsic π shift for real-time common-mode rejection, this technique effectively suppresses low-frequency noise and pushes the 1/ f corner frequency down to 1 Hz, with a measured sensitivity at 1 Hz of 10.6 pT·Hz –1/2 . The magnetometer also exhibits excellent capability in detecting magnetic anomalies, promoting the practical use of diamond quantum sensors in biomedical, geophysical, and other real-world applications.