Entanglement-enhanced AC magnetometry in the presence of Markovian noises

TL;DR

This paper demonstrates that entanglement, specifically GHZ states, can enhance the detection of AC magnetic fields in noisy environments with Markovian decoherence, surpassing classical limits and broadening detection bandwidth.

Contribution

It introduces a method using GHZ states to improve entanglement-enhanced AC magnetometry under parallel Markovian noise, especially for detuned Rabi oscillations.

Findings

GHZ states significantly boost AC magnetic field detection sensitivity.

The interaction time scales as 1/L, improving bandwidth for frequency detection.

Entanglement provides advantages in noisy environments for AC, not DC, magnetic field sensing.

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 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 open up the way for new applications of entanglement-enhanced AC magnetometry.