CutQC: using small Quantum computers for large Quantum circuit evaluations
CutQC is introduced, a scalable hybrid computing approach that combines classical computers and quantum computers to enable evaluation of quantum circuits that cannot be run on classical or quantum computers alone and offers significant runtime speedup compared with the only viable current alternative—purely classical simulations.
Abstract
Quantum computing (QC) is a new paradigm offering the potential of\nexponential speedups over classical computing for certain computational\nproblems. Each additional qubit doubles the size of the computational state\nspace available to a QC algorithm. This exponential scaling underlies QC's\npower, but today's Noisy Intermediate-Scale Quantum (NISQ) devices face\nsignificant engineering challenges in scalability. The set of quantum circuits\nthat can be reliably run on NISQ devices is limited by their noisy operations\nand low qubit counts.\n This paper introduces CutQC, a scalable hybrid computing approach that\ncombines classical computers and quantum computers to enable evaluation of\nquantum circuits that cannot be run on classical or quantum computers alone.\nCutQC cuts large quantum circuits into smaller subcircuits, allowing them to be\nexecuted on smaller quantum devices. Classical postprocessing can then\nreconstruct the output of the original circuit. This approach offers\nsignificant runtime speedup compared with the only viable current\nalternative--purely classical simulations--and demonstrates evaluation of\nquantum circuits that are larger than the limit of QC or classical simulation.\nFurthermore, in real-system runs, CutQC achieves much higher quantum circuit\nevaluation fidelity using small prototype quantum computers than the\nstate-of-the-art large NISQ devices achieve. Overall, this hybrid approach\nallows users to leverage classical and quantum computing resources to evaluate\nquantum programs far beyond the reach of either one alone.\n