Noise-resistant quantum state compression readout

Qubit measurement is generally the most error-prone operation that degrades the performance of near-term quantum devices,and the exponential decay of readout fidelity severely impedes the development of large-scale quantum information processing.Given these disadvantages, we present a quantum state readout method, named compression readout, that naturally avoids large multi-qubit measurement errors by compressing the quantum state into a single qubit for measurement. Our method generally outperforms direct measurements in terms of accuracy, and the advantage grows with the system size. Moreover, because only one-qubit measurements are performed, our method requires solely a fine readout calibration on one qubit and is free of correlated measurement error, which drastically diminishes the demand for device calibration. These advantages suggest that our method can immediately boost the readout performance of near-term quantum devices and will greatly benefit the development of large-scale quantum computing.

在61比特可编程超导量子处理器上对量子多体态进行量子神经元感知

对具有不同性质和物相的多体量子态进行分类是量子多体物理学中最基本的任务之一.然而,由于巨大数量的相互作用的粒子所产生的指数级的复杂性,大规模量子态的分类对于经典的方法来说极具挑战性.本文提出了一种新的方法,称为量子神经元感知.利用一个61比特的超导量子处理器作为演示,作者表明该方案可以有效地对两种不同类型的多体现象,即遍历相和局域相,进行分类.量子神经元感知过程使他们能够通过只测量一个量子比特来区分这些多体物相,并提供比传统方法(如测量不平衡度)更好的分辨率.本研究证明了量子神经元感知在近期量子处理器应用的可行性和扩展性,并为探索更大规模系统中的量子多体现象开辟了新的途径.

基于量子干涉消除量子点纠缠光子源时间关联的研究

作为高效率的确定性固态量子光源,半导体量子点展现了具有高纠缠保真度的偏振纠缠光子发射,并被应用于量子信息领域.但是,在级联跃迁产生纠缠光子的过程中,时间关联效应会导致光子的不可分辨性受限,因此极大地限制了半导体量子点在多光子实验中的可拓展性.本文通过在偏振分束器上进行量子干涉,量子点发射光子的偏振自由度和时间自由度发生了分离,从而消除了时间关联对偏振纠缠的影响.基于以上方案,在实验上,四光子Greenberger-Horne-Zeilinger(GHZ)态保真度从(58.7±2.2)%提升至(75.5±2.0)%.这项工作展现了利用半导体量子点纠缠光子源有望实现可拓展、高品质的多光子纠缠态,从而促进光学量子信息的发展.