Simulating Large Quantum Circuits on a Small Quantum Computer
Simulating Large Quantum Circuits on a Small Quantum Computer
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DOI：
10.1103/physrevlett.125.150504
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发表时间：
2020-10-06
影响因子：
8.6
通讯作者：
Wu, Xiaodi
中科院分区：
文献类型：
--
作者：
Peng, Tianyi;Harrow, Aram W.;Wu, Xiaodi
有限的量子记忆是近期量子设备最重要的约束之一。理论和实际重要性是了解小量子计算机是否可以模拟更大的量子系统，或者执行比可用的量子更多的算法要多于可用的量子。在这封信中，我们引入了量子电路的群集参数K和D。这样的电路的张量网络最多可以将最多d的大小簇分解为群集间量子通信。我们提出了一个群集模拟方案，该方案可以在D-Qubit机器上模拟任何（k，d）聚集的量子电路，大约有2（o（k）），当考虑到更多细粒电路结构时，可能会进一步加速。我们展示了如何使用我们的方案来模拟聚类的量子系统，就像大分子一样 - 可以将它们分为多个显着较小的群集，它们之间的相互作用较弱。通过使用合适的聚类ANSATZ，我们还实验表明，量子变异的eigensolver仍然可以实现所需的性能，以估算Beh2分子的能量，同时在物理量子设备上运行，所需的量子数为一半。
Limited quantum memory is one of the most important constraints for near-term quantum devices. Understanding whether a small quantum computer can simulate a larger quantum system, or execute an algorithm requiring more qubits than available, is both of theoretical and practical importance. In this Letter, we introduce cluster parameters K and d of a quantum circuit. The tensor network of such a circuit can be decomposed into clusters of size at most d with at most K qubits of inter-cluster quantum communication. We propose a cluster simulation scheme that can simulate any (K, d)-clustered quantum circuit on a d-qubit machine in time roughly 2(O(K)), with further speedups possible when taking more fine-grained circuit structure into account. We show how our scheme can be used to simulate clustered quantum systems-such as large molecules-that can be partitioned into multiple significantly smaller clusters with weak interactions among them. By using a suitable clustered ansatz, we also experimentally demonstrate that a quantum variational eigensolver can still achieve the desired performance for estimating the energy of the BeH2 molecule while running on a physical quantum device with half the number of required qubits.