Title | Simulating large quantum circuits on a small quantum computer |

Publication Type | Journal Article |

Year of Publication | 2020 |

Authors | Peng, T, Harrow, A, Ozols, M, Wu, X |

Journal | Phys. Rev. Lett. |

Volume | 125 |

Issue | 150504 |

Date Published | 12/8/2020 |

Abstract | 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. |

URL | https://arxiv.org/abs/1904.00102 |

DOI | 10.1103/PhysRevLett.125.150504 |