



01588nas a2200157   4500008004100000245006600041210006600107260001400173490000800187520113200195100001701327700001701344700001701361700001501378856003701393       2020                        eng d00aSimulating large quantum circuits on a small quantum computer0 aSimulating large quantum circuits on a small quantum computer  c12/8/20200 v1253 a<p>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. Our main result is a simulation scheme of any (K,d)-clustered quantum circuit on a d-qubit machine in time roughly 2O(K). An important application of our result is the simulation of clustered quantum systems---such as large molecules---that can be partitioned into multiple significantly smaller clusters with weak interactions among them. Another potential application is quantum optimization: we demonstrate numerically that variational quantum eigensolvers can still perform well when restricted to clustered circuits, thus making it feasible to study large quantum systems on small quantum devices.</p>1 aPeng, Tianyi1 aHarrow, Aram1 aOzols, Maris1 aWu, Xiaodi  uhttps://arxiv.org/abs/1904.00102