Optimal Purification of a Spin Ensemble by Quantum-Algorithmic Feedback
Optimal Purification of a Spin Ensemble by Quantum-Algorithmic Feedback
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DOI：
10.1103/physrevx.12.031014
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发表时间：
2022-07-21
影响因子：
12.5
通讯作者：
Gangloff, Dorian A.
中科院分区：
文献类型：
--
作者：
Jackson, Daniel M.;Haeusler, Urs;Gangloff, Dorian A.
将量子粒子的高温系综纯化到已知状态是利用量子多体效应的关键要求。被动冷却的替代方案是主动反馈，它使系统稳定在选定的目标状态。这种替代方案如果实现，将为量子态的设计提供额外的控制能力。在这里，我们提出了一个反馈算法应用于量子系统，这是能够稳定的集体状态的系综从其最大熵状态的限制，单量子涨落。我们的算法方法最大限度地提高了系统的状态净化率？的物理常数，因此，它仍然是最佳的反馈方法，即使在耗散和无序的存在。我们通过实验测试了这种反馈在半导体量子点的高度非均匀核自旋系综上的鲁棒性，将核自旋波动降低了83倍，降至5.7（2）自旋宏观态。模拟表明，没有系统特定的不均匀性，我们的算法可以净化系统的单自旋波动。此外，我们利用我们的算法方法来定制超越简单极化的非平凡核自旋分布，包括加权双峰和晶格多稳态。这种控制是量子相关宏观态的先驱，我们的算法的扩展版本可以在均匀系统中生成。
Purifying a high-temperature ensemble of quantum particles toward a known state is a key requirement to exploit quantum many-body effects. An alternative to passive cooling, which brings a system to its ground state, is active feedback, which stabilizes the system at a chosen target state. This alternative, if realized, offers additional control capabilities for the design of quantum states. Here we present a feedback algorithm applied to a quantum system, which is capable of stabilizing the collective state of an ensemble from its maximum entropy state to the limit of single quantum fluctuations. Our algorithmic approach maximizes the rate of state purification given the system???s physical constants; thus it remains the optimal feedback approach even in the presence of dissipation and disorder. We test experimentally the robustness of this feedback on the highly inhomogeneous nuclear-spin ensemble of a semiconductor quantum dot, reducing nuclear-spin fluctuations 83-fold, down to 5.7(2) spin macrostates. Simulations demonstrate that without system-specific inhomogeneities, our algorithm can purify the system down to single-spin fluctuations. Further, we exploit our algorithmic approach to tailor nontrivial nuclear-spin distributions that go beyond simple polarization, including weighted bimodality and latticed multistability. This control is a precursor toward quantum-correlated macrostates, which an extended version of our algorithm could generate in homogeneous systems.