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arXiv:2401.13879 · Physical Review A

Enhancing weak-magnetic-field sensing of a cavity-magnon system with dual frequency modulation

Zheng Liu, Yu‐qiang Liu, Zi-yi Mai, Yi‐jia Yang, Nan-nan Zhou, Chang‐shui Yu

Published Feb 12, 2024• 12 citations
arXivHTMLPDF

Abstract

The crucial limitation of improving the sensitivity of the detection of weak magnetic fields is the unavoidable measurement noise. In this paper, we propose a scheme to achieve precise sensing robust against additional noise by employing a dual frequency bias field modulation within a cavity-magnon system. We find that the antirotating wave term can amplify the signal of the detected magnetic field, but this amplification effect must coexist with the rotating wave term. In particular, by the bias field modulation, we find the robustness against cavity field thermal noise is substantially enhanced, quantum noise and cavity field thermal noise is greatly reduced, and the external magnetic field signal is amplified, thereby improving the weak-magnetic-field sensing system's sensitivity. Compared with the previous scheme, our scheme requires neither an ultrastrong- or deep-strong-coupling mechanism nor the suppression of the additional noise by increasing the electromagnetic cooperativity. Our scheme could provide a valuable candidate for weak-magnetic-field sensing.

DOI
10.1103/physreva.109.023709

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The crucial limitation of improving the sensitivity of the detection of weak magnetic fields is the unavoidable measurement noise. In this paper, we propose a scheme to achieve precise sensing robust against additional noise by employing a dual frequency bias field modulation within a cavity-magnon system. We find that the antirotating wave term can amplify the signal of the detected magnetic field, but this amplification effect must coexist with the rotating wave term. In particular, by the bias field modulation, we find the robustness against cavity field thermal noise is substantially enhanced, quantum noise and cavity field thermal noise is greatly reduced, and the external magnetic field signal is amplified, thereby improving the weak-magnetic-field sensing system's sensitivity. Compared with the previous scheme, our scheme requires neither an ultrastrong- or deep-strong-coupling mechanism nor the suppression of the additional noise by increasing the electromagnetic cooperativity. Our scheme could provide a valuable candidate for weak-magnetic-field sensing.
A scheme of an ultra-sensitive magnetometer in the cavity quantum electromagnonics where the intracavity microwave mode coupled to a magnonic mode via magnetic dipole interaction is proposed. It is shown that by driving both magnonic and microwave modes with external classical fields and controlling the system parameters, one can reduce the added noise of magnetic field measurement below the standard quantum limit (SQL). Surprisingly, we show that beyond the rotating wave approximation (RWA), not only the added noise can be suppressed, but also the output cavity response to the input signal can be substantially amplified in order to achieve a precise magnetic-field measurement. The sensitivity of the proposed magnetic amplifier-sensor is approximately in the order of 10−18T/Hz10^{-18}T/\sqrt{Hz}10−18T/Hz​ which is competitive compared to the current state-of-the-art magnetometers like superconducting quantum interference devices (SQUIDs) and atomic magnetometers. The advantage of the proposed sensor in comparison with the other magnetometers is its high sensitivity at room temperature and sensing in a wide range of frequency up to MHz as well as its capability to signal-response amplification.
A scheme of an ultrasensitive magnetometer in the cavity quantum electromagnonics is proposed, where the intracavity microwave mode is coupled to a magnonic mode via magnetic dipole interaction. It is shown that by driving both magnonic and microwave modes with external classical fields and controlling the system parameters, one can reduce the added noise of magnetic field measurement below the standard quantum limit (SQL). Surprisingly, we show that beyond the rotating wave approximation (RWA), not only can the added noise be suppressed but also the output cavity response to the input signal can be substantially amplified in order to achieve a precise magnetic-field measurement. The estimated theoretical sensitivity of the proposed magnetic amplifier-sensor is approximately on the order of ${10}^{\ensuremath{-}18}\phantom{\rule{0.28em}{0ex}}\mathrm{T}/\sqrt{\mathrm{Hz}}$, which is competitive compared to the current state-of-the-art magnetometers like superconducting quantum interference devices (SQUIDs) and atomic magnetometers. The advantages of the proposed sensor in comparison with the other magnetometers is its high sensitivity at room temperature, sensing in a wide range of frequencies up to MHz, and its capability for signal-response amplification.
ABSTRACT We propose a scheme to achieve exponential amplification of weak magnetic‐field signals and significant suppression of additional noise in a cavity magnonics. By introducing a two‐photon pump field and constructing single‐quadrature coupling between modes in the squeezed representation, a significant enhancement of the signal response based on quantum nondemolition measurement can be achieved. Fine‐tuning the squeezing parameters of the pump field enables the realization of high signal response under both strong and weak cavity‐magnon coupling regimes, thereby enhancing the controllability of the sensor. In addition, by introducing an auxiliary broadband squeezed source, the additional noise can be suppressed far below the standard quantum limit (SQL) through quantum destructive interference between the two noise fields, thereby significantly enhancing the sensor's performance. This scheme, combining exponential signal amplification with significant noise suppression, offers a powerful platform for the development of quantum sensors and advances in quantum precision measurements.
We developed a highly sensitive and long-term stable diamond quantum magnetometer by integrating a dual-feedback system that compensates for common- and differential-mode frequency shifts in double-quantum (DQ) 4-Ramsey interferometry. Detecting extremely weak magnetic-field signals requires extensive signal accumulation to enhance the signal-to-noise ratio. However, deviations from the optimal operating frequencies caused by thermal drift or environmental magnetic noise severely hinder the long-term stability of such a sensing system. To overcome the limitation, we first derived analytical solutions for the signal response to common- and differential-mode detunings based on a detuning-inclusive Hamiltonian to theoretically clarify the robustness limit in DQ 4-Ramsey sensing. Guided by this theoretical model, we introduced synchronized frequency modulation and a dual-feedback scheme to independently track and compensate for these frequency shifts while maintaining an optimal magnetic-field response. The proposed method enabled stable continuous operation against temperature variations of 2.8 K. By maintaining a magnetic field sensitivity of 7.0 pT/Hz^1/2 in the frequency range of 5-100 Hz for a prolonged duration of 4 hours, we achieved an extremely low noise floor of 64 fT/Hz^1/2. During prolonged continuous sensing, the system exhibited the expected 1/T^1/2 scaling with integration time T, and prevented both the underestimation of amplitude and waveform distortion. These results establish a robust approach for long-term DQ 4-Ramsey diamond magnetometry and demonstrate its potential for detecting weak biomagnetic signals.
Abstract Quantum metrology enables measurement sensitivities beyond classical limits by exploiting quantum resources. Among promising platforms, hybrid cavity–magnon systems—where microwave photons interact with collective spin excitations in magnetic materials—offer a versatile testbed for emerging quantum technologies. However, their performance hinges on precise knowledge of the cavity–magnon coupling strength. Here, we propose an experimentally feasible scheme to enhance the quantum estimation of this parameter by leveraging coherent feedback and parametric amplification. Using the Heisenberg–Langevin formalism, we linearize the system dynamics and compute both quantum (QFI) and classical Fisher information. Our analysis shows that optimal detuning, strong driving, and cryogenic temperatures below 0.1 K significantly improve estimation precision, while magnon dissipation and thermal noise degrade the QFI. Parametric amplification enhances precision when the gain and phase are optimally tuned, and coherent feedback yields even greater sensitivity at tailored phase shifts and reflectivities. Notably, their combination achieves the lowest estimation error and the highest robustness against thermal noise. Finally, we identify the cavity mode as the optimal probe, with homodyne detection nearly saturating the quantum limit under ideal conditions. These findings establish a robust pathway for high-precision, noise-resilient cavity–magnon coupling estimation.
Magnons, as fundamental quasiparticles that emerge in elementary spin excitations, hold a big promise for innovating quantum technologies in information coding and processing. By establishing the exact relation between Fisher information and entanglement in partially accessible metrological schemes, we rigorously prove that bipartite entanglement plays a crucial role during the dynamical encoding process. However, the presence of an entanglement during the measurement process unavoidably reduces the ultimate measurement precision. These findings are verified in an experimentally feasible cavity magnonic system engineered for detecting a weak magnetic field by performing precision measurements through the cavity field. Moreover, we further demonstrate that, within a weak-coupling region, measurement precision can reach the Heisenberg limit. Additionally, quantum criticality also enables us to enhance measurement precision in a strong-coupling region.