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arXiv:2309.00177

Enhanced quantum sensing with amplification and deamplification

Min Jiang, Yushu Qin, Yuanhong Wang, Ying Huang, Xinhua Peng, Dmitry Budker

Published Sep 1, 2023• 3 citations
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Abstract

Quantum sensing is a fundamental building block of modern technology that employs quantum resources and creates new opportunities for precision measurements. However, previous methods usually have a common assumption that detection noise levels should be below the intrinsic sensitivity provided by quantum resources. Here we report the first demonstration of Fano resonance between coupled alkali-metal and noble gases through rapid spin-exchange collisions. The Fano resonance gives rise to two intriguing phenomena: spin amplification and deamplification, which serve as crucial resources for enhanced sensing. Further we develop a novel scheme of quantum sensing enhanced by amplification and deamplification, with relaxed requirements on the detection noise. The coupled systems of alkali-metal and noble gases act as amplifiers or de-amplifiers, enabling to extract small signals above the detection noise before final detection. We demonstrate magnetic-field measurement about 54 decibels below the photon-shot noise, which outperforms the state-of-the-art squeezed-light technology and realizes femtotesla-level sensitivity. Our work opens new avenues to applications in searches for ultralight dark matter with sensitivity well beyond the supernova-observation constraints.

DOI
10.48550/arxiv.2309.00177

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Quantum amplification is recognized as a key resource for precision measurements. However, most conventional paradigms employ an ensemble of independent particles that usually limit the performance of quantum amplification in gain, spectral linewidth, etc. Here we demonstrate a new signal amplification using cooperative 129Xe nuclear spins embedded within a feedback circuit, where the noble-gas spin coherence time is enhanced by at least one order of magnitude. Using such a technique, magnetic field can be substantially pre-enhanced by more than three orders and is in situ readout with an embedded 87Rb magnetometer. We realize an ultrahigh magnetic sensitivity of 4.0 fT/Hz1/2^{1/2}1/2 that surpasses the photon-shot noise and even below the spin-projection noise of the embedded atomic magnetometer, allowing for exciting applications including searches for dark matter with sensitivity well beyond supernova constraints. Our findings extend the physics of quantum amplification to cooperative spin systems and can be generalized to a wide variety of existing sensors, enabling a new class of cooperative quantum sensors.
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Quantum sensing is crucial for precision measurements, yet quantum sensor sensitivity is often limited by the coherence time of the quantum system. Here, we demonstrate a method to enhance coherence time through cooperative spins. Using a tunable feedback circuit, we induce cooperation among noble-gas ^{129}Xe spins, resulting in an impressive 18-fold coherence enhancement. Moreover, we show that the cooperative ^{129}Xe spins can significantly amplify magnetic signals by at least 3 orders of magnitude. Magnetic field sensing assisted with such a cooperative spin amplifier realizes the sensitivity of 4 fT/Hz^{1/2} and surpasses the spin-projection noise of the embedded ^{87}Rb spin gas magnetometer. These results pave the way for a new class of "cooperative quantum sensors," and open up exciting prospects in fundamental physics.
Precision molecular spectroscopy provides a sensitive detection method for ultralight bosonic dark matter. This wavelike dark matter couples to the Standard Model fundamental constants, modulates the frequencies of the molecular transitions and of the resonances of the optical cavities, and brings oscillations in the laser absorption spectroscopy signals. Spectroscopy experiments with differential detection methods approach the fundamental limitation imposed by quantum noise in photodetection. The use of squeezed light in spectroscopy is addressed here to circumvent this limitation. An experimental setup is proposed for the interrogation of an acetylene transition at 1542 nm with a bright squeezed light field and a homodyne detection scheme. This approach enables measurements using the squeezed quadrature, ensures broadband sensitivity, demonstrates robustness to moderate losses, and provides improved constraints for the couplings of the ultralight bosonic dark matter to the Standard Model in the radiofrequency range.