量子系统的部分测量

J. Monroe
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引用次数: 1

摘要

射影测量是量子力学中常用的假设。然而,量子测量技术的进步允许部分测量,在保持波函数完整的情况下准确地估计状态信息。在本文中,我们采用部分测量来研究两种现象。首先,我们以海森堡1929年思想实验的方式研究了一种不确定性关系,除了投影测量外,还包括部分测量。我们发现弱部分测量可以降低两个不相容(不可交换)观测值之间的不确定度。在第二项研究中,我们研究了由部分测量引起的不可逆动力学的基础。我们通过比较因果顺序和反向因果顺序的后选择反馈协议产生的测量结果的正向和时间反向概率来做到这一点。我们发现部分测量的统计量根据广义热力学第二定律产生熵。我们使用超导量子比特进行这些实验。本文还描述了这些器件的制造过程,并详细介绍了一种新的制造技术,该技术可以实现约瑟夫森结超导电路的快速单步光刻。与传统的电子束光刻相比,该技术通过使用直接写入光刻系统简化了处理过程。尽管其光刻面积大,但用这种方法制成的约瑟夫森结具有低临界电流和高相干时间。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
Partial Measurements of Quantum Systems
Projective measurement is a commonly used assumption in quantum mechanics. However, advances in quantum measurement techniques allow for partial measurements, which accurately estimate state information while keeping the wavefunction intact. In this dissertation, we employ partial measurements to study two phenomena. First, we investigate an uncertainty relation -- in the style of Heisenberg's 1929 thought experiment -- which includes partial measurements in addition to projective measurements. We find that a weak partial measurement can decrease the uncertainty between two incompatible (non-commuting) observables. In the second study, we investigate the foundation of irreversible dynamics resulting from partial measurements. We do so by comparing the forward and time-reversed probabilities of measurement outcomes resulting from post-selected feedback protocols with both causal and reversed-causal order. We find that the statistics of partial measurements produce entropy in accordance with generalized second laws of thermodynamics. We perform these experiments using superconducting qubits. This dissertation also describes the fabrication process for these devices and details a novel fabrication technique that allows fast, single-step lithography of Josephson-junction superconducting circuits. The technique simplifies processing by utilizing a direct-write photolithography system, in contrast to traditional electron-beam lithography. Despite their large lithographic area, Josephson junctions made with this method have low critical currents and high coherence times.
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