日本东京大学Thanaporn Sichanugrist团队研究了马尔可夫噪声下的纠缠增强交流磁测。相关论文于2025年4月7日发表在《物理评论A》杂志上。

纠缠是提高量子传感器灵敏度的一种资源。在理想情况下，使用纠缠态作为探测目标场的探针，人们可以突破所有经典传感器的标准量子极限。然而，由于纠缠对退相干是脆弱的，因此尚不清楚纠缠增强计量在嘈杂的环境中是否有用。在平行马尔可夫退相干效应下估计直流磁场的振幅时，其益处确实有限，其中噪声算子平行于目标场。相反，当研究组试图检测交流磁场时，在平行马尔可夫退相干的影响下，发现使用纠缠比经典策略更有优势。

研究组考虑一个场景，用目标交流磁场诱导量子比特的拉比振荡。虽然原则上他们可以根据拉比振荡估计交流磁场的振幅，但如果量子比特频率与交流磁场频率明显失谐，信号就会变弱。研究组证明，通过使用Greenberger-Hone-Zeilinger（GHZ）态，即使在平行马尔可夫退相干的影响下，也可以显著增强失谐拉比振荡的信号。

该方法基于这样一个事实，即GHZ态和交流磁场之间的相互作用时间按1/L缩放，以减轻退相干效应，其中L是量子比特的数量，这有助于提高交流磁场可检测频率的带宽。该研究结果为纠缠增强交流磁测的新应用铺平了道路。

附：英文原文

Title: Entanglement-enhanced ac magnetometry in the presence of Markovian noise

Author: Thanaporn Sichanugrist, Hajime Fukuda, Takeo Moroi, Kazunori Nakayama, So Chigusa, Norikazu Mizuochi, Masashi Hazumi, Yuichiro Matsuzaki

Issue&Volume: 2025/04/07

Abstract: Entanglement is a resource to improve the sensitivity of quantum sensors. In an ideal case, using an entangled state as a probe to detect target fields, we can beat the standard quantum limit by which all classical sensors are bounded. However, since entanglement is fragile against decoherence, it is unclear whether entanglement-enhanced metrology is useful in a noisy environment. Its benefit is indeed limited when estimating the amplitude of dc magnetic fields under the effect of parallel Markovian decoherence, where the noise operator is parallel to the target field. In this paper, on the contrary, we show an advantage to using an entanglement over the classical strategy under the effect of parallel Markovian decoherence when we try to detect ac magnetic fields. We consider a scenario to induce a Rabi oscillation of the qubits with the target ac magnetic fields. Although we can, in principle, estimate the amplitude of the ac magnetic fields from the Rabi oscillation, the signal becomes weak if the qubit frequency is significantly detuned from the frequency of the ac magnetic field. We show that, by using the Greenberger-Horne-Zeilinger (GHZ) states, we can significantly enhance the signal of the detuned Rabi oscillation even under the effect of parallel Markovian decoherence. Our method is based on the fact that the interaction time between the GHZ states and ac magnetic fields scales as 1/L to mitigate the decoherence effect, where L is the number of qubits, which contributes to improving the bandwidth of the detectable frequencies of the ac magnetic fields. Our results pave the way for new applications of entanglement-enhanced ac magnetometry.

DOI: 10.1103/PhysRevA.111.042605

Source: https://journals.aps.org/pra/abstract/10.1103/PhysRevA.111.042605