分类： 光学 >> 量子光学 提交时间： 2023-02-19
摘要： In a fully-controllable experiment platform for studying non-Markovian open quantum dynamics, we show that the non-Markovianity could be investigated from the global and local aspects. By mixing random unitary dynamics, we demonstrate non-Markovian and Markovian open quantum dynamics. From the global point of view, by tuning the base frequency we demonstrate the transition from the Markovianity to the non-Markovianity as measured by the quantum mutual information (QMI). In a Markovian open quantum process, the QMI decays monotonically, while it may rise temporarily in a non-Markovian process. However, under some circumstances, it is not sufficient to globally investigate the non-Markovianity of the open quantum dynamics. As an essential supplement, we further utilize the quantum Fisher information (QFI) flow to locally characterize the non-Markovianity in different channels. We demonstrate that the QMI in combination with the QFI flow are capable of measuring the non-Markovianity for a multi-channel open quantum dynamics.
分类： 光学 >> 量子光学 提交时间： 2023-02-19
Xinyue Long
Wan-Ting He
Na-Na Zhang
Kai Tang
Zidong Lin
Hongfeng Liu
Xinfang Nie
Guanru Feng
Jun Li
Tao Xin
Qing Ai
Dawei Lu
摘要： In open quantum systems, the precision of metrology inevitably suffers from the noise. {In Markovian open quantum dynamics, the precision can not be improved by using entangled probes although the measurement time is effectively shortened.} However, it was predicted over one decade ago that in a non-Markovian one, the error can be significantly reduced by the quantum Zeno effect (QZE) [Chin, Huelga, and Plenio, Phys. Rev. Lett. \textbf{109}, 233601 (2012)]. In this work, we apply a recently-developed quantum simulation approach to experimentally verify that entangled probes can improve the precision of metrology by the QZE. Up to $n=7$ qubits, we demonstrate that the precision has been improved by a factor of $n^{1/4}$, which is consistent with the theoretical prediction. Our quantum simulation approach may provide an intriguing platform for experimental verification of various quantum metrology schemes.
分类： 光学 >> 量子光学 提交时间： 2023-02-19
摘要： Quantum metrology aims to use quantum resources to improve the precision of measurement. Quantum criticality has been presented as a novel and efficient resource. Generally, protocols of criticality-based quantum metrology often work without decoherence. In this paper, we address the issue whether the divergent feature of the inverted variance is indeed realizable in the presence of noise when approaching the QPT. Taking the quantum Rabi model (QRM) as an example, we obtain the analytical result for the inverted variance. We show that the inverted variance may be convergent in time due to the noise. When approaching the critical point, the maximum inverted variance demonstrates a power-law increase with the exponent -1.2, of which the absolute value is smaller than that for the noise-free case, i.e., 2. We also observe a power-law dependence of the maximum inverted variance on the relaxation rate and the temperature. Since the precision of the metrology is very sensitive to the noise, as a remedy, we propose performing the squeezing operation on the initial state to improve the precision under decoherence. In addition, we also investigate the criticality-based metrology under the influence of the two-photon relaxation. Contrary to the single-photon relaxation, the quantum dynamics of the inverted variance shows a completely-different behavior. It does not oscillate with the same frequency with respect to the re-scaled time for different dimensionless coupling strengths. Strikingly, although the maximum inverted variance still manifests a power-law dependence on the energy gap, the exponent is positive and depends on the dimensionless coupling strength. This observation implies that the criticality may not enhance but weaken the precision in the presence of two-photon relaxation. It can be well described by the non-linearity introduced by the two-photon relaxation.
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