Université Lyon, ENS de Lyon, Université Claude Bernard Lyon 1, CNRS, Laboratoire de Physique, F-69342, Lyon, France.
Laboratoire Pierre Aigrain, Département de physique de l'ENS, École normale supérieure, PSL Research University, Université Paris Diderot, Sorbonne Paris Cité, Sorbonne Universités, UPMC Univ. Paris 06, CNRS, 75005, Paris, France.
Nat Commun. 2018 May 15;9(1):1926. doi: 10.1038/s41467-018-04372-9.
Decoherence originates from the leakage of quantum information into external degrees of freedom. For a qubit, the two main decoherence channels are relaxation and dephasing. Here, we report an experiment on a superconducting qubit where we retrieve part of the lost information in both of these channels. We demonstrate that raw averaging the corresponding measurement records provides a full quantum tomography of the qubit state where all three components of the effective spin-1/2 are simultaneously measured. From single realizations of the experiment, it is possible to infer the quantum trajectories followed by the qubit state conditioned on relaxation and/or dephasing channels. The incompatibility between these quantum measurements of the qubit leads to observable consequences in the statistics of quantum states. The high level of controllability of superconducting circuits enables us to explore many regimes from the Zeno effect to underdamped Rabi oscillations depending on the relative strengths of driving, dephasing, and relaxation.
退相干源于量子信息泄露到外部自由度。对于一个qubit，两个主要的退相干通道是弛豫和消相。在这里，我们报告了一个超导 qubit 的实验，我们在这两个通道中恢复了部分丢失的信息。我们证明，对相应的测量记录进行原始平均可以提供 qubit 状态的完整量子层析成像，其中有效自旋 1/2 的所有三个分量同时被测量。从实验的单次实现中，可以推断出量子轨迹，这些轨迹是根据弛豫和/或消相通道对 qubit 状态进行条件化的。qubit 的这些量子测量之间的不兼容性导致量子状态的统计数据中出现可观察的结果。超导电路的高度可控性使我们能够根据驱动、消相和弛豫的相对强度，从 Zeno 效应到欠阻尼的 Rabi 振荡探索许多状态。
