Department of Physics, University of Wisconsin-Madison, Madison, WI 53706, USA.
Department of Physics, Syracuse University, Syracuse, NY 13244, USA.
Science. 2018 Sep 21;361(6408):1239-1242. doi: 10.1126/science.aat4625. Epub 2018 Sep 20.
Fast, high-fidelity measurement is a key ingredient for quantum error correction. Conventional approaches to the measurement of superconducting qubits, involving linear amplification of a microwave probe tone followed by heterodyne detection at room temperature, do not scale well to large system sizes. We introduce an approach to measurement based on a microwave photon counter demonstrating raw single-shot measurement fidelity of 92%. Moreover, the intrinsic damping of the photon counter is used to extract the energy released by the measurement process, allowing repeated high-fidelity quantum nondemolition measurements. Our scheme provides access to the classical outcome of projective quantum measurement at the millikelvin stage and could form the basis for a scalable quantum-to-classical interface.
快速、高保真度的测量是量子纠错的关键组成部分。传统的超导量子比特测量方法涉及微波探针信号的线性放大，然后在室温下进行外差检测，这种方法很难扩展到大规模系统。我们引入了一种基于微波光子计数器的测量方法，该方法实现了原始单拍测量保真度为 92%。此外，光子计数器的固有阻尼用于提取测量过程中释放的能量，从而实现重复的高保真量子非破坏测量。我们的方案为在毫开尔文阶段实现投影量子测量的经典结果提供了途径，并可能成为可扩展的量子-经典接口的基础。
