CutQC: Using Small Quantum Computers for Large Quantum Circuit Evaluations

TL;DR

CutQC is a hybrid quantum-classical method that partitions large quantum circuits into smaller parts for execution on limited quantum hardware, enabling the evaluation of bigger circuits with higher fidelity than current NISQ devices.

Contribution

The paper introduces CutQC, a novel hybrid approach that enables large quantum circuit evaluation by partitioning circuits and combining classical postprocessing, surpassing current hardware limitations.

Findings

Enables evaluation of larger quantum circuits than current hardware allows.

Achieves higher fidelity in quantum circuit evaluation on small quantum computers.

Provides significant runtime speedup over classical simulation methods.

Abstract

Quantum computing (QC) is a new paradigm offering the potential of exponential speedups over classical computing for certain computational problems. Each additional qubit doubles the size of the computational state space available to a QC algorithm. This exponential scaling underlies QC's power, but today's Noisy Intermediate-Scale Quantum (NISQ) devices face significant engineering challenges in scalability. The set of quantum circuits that can be reliably run on NISQ devices is limited by their noisy operations and low qubit counts. This paper introduces CutQC, 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. CutQC cuts large quantum circuits into smaller subcircuits, allowing them to be executed on smaller quantum devices. Classical postprocessing can then reconstruct the output of the original circuit. This approach offers significant runtime speedup compared with the only viable current alternative--purely classical simulations--and demonstrates evaluation of quantum circuits that are larger than the limit of QC or classical simulation. Furthermore, in real-system runs, CutQC achieves much higher quantum circuit evaluation fidelity using small prototype quantum computers than the state-of-the-art large NISQ devices achieve. Overall, this hybrid approach allows users to leverage classical and quantum computing resources to evaluate quantum programs far beyond the reach of either one alone.