Boixo Sergio, Smelyanskiy Vadim N, Shabani Alireza, Isakov Sergei V, Dykman Mark, Denchev Vasil S, Amin Mohammad H, Smirnov Anatoly Yu, Mohseni Masoud, Neven Hartmut
Google, Venice, California 90291, USA.
NASA Ames Research Center, Moffett Field, California 94035, USA.
Nat Commun. 2016 Jan 7;7:10327. doi: 10.1038/ncomms10327.
Quantum tunnelling is a phenomenon in which a quantum state traverses energy barriers higher than the energy of the state itself. Quantum tunnelling has been hypothesized as an advantageous physical resource for optimization in quantum annealing. However, computational multiqubit tunnelling has not yet been observed, and a theory of co-tunnelling under high- and low-frequency noises is lacking. Here we show that 8-qubit tunnelling plays a computational role in a currently available programmable quantum annealer. We devise a probe for tunnelling, a computational primitive where classical paths are trapped in a false minimum. In support of the design of quantum annealers we develop a nonperturbative theory of open quantum dynamics under realistic noise characteristics. This theory accurately predicts the rate of many-body dissipative quantum tunnelling subject to the polaron effect. Furthermore, we experimentally demonstrate that quantum tunnelling outperforms thermal hopping along classical paths for problems with up to 200 qubits containing the computational primitive.
量子隧穿是一种量子态穿越高于其自身能量的能量势垒的现象。量子隧穿已被假设为量子退火优化中的一种有利物理资源。然而，尚未观察到多量子比特的计算隧穿，并且缺乏关于高频和低频噪声下协同隧穿的理论。在此，我们表明8量子比特隧穿在当前可用的可编程量子退火器中发挥着计算作用。我们设计了一种用于隧穿的探针，这是一种计算原语，其中经典路径被困在一个错误的最小值中。为支持量子退火器的设计，我们在现实噪声特性下开发了一种开放量子动力学的非微扰理论。该理论准确预测了受极化子效应影响的多体耗散量子隧穿速率。此外，我们通过实验证明，对于包含该计算原语且多达200个量子比特的问题，量子隧穿在穿越经典路径时比热跳跃表现更优。
