Verified delegated quantum computation requires techniques beyond cut-and-choose

TL;DR

This paper demonstrates that relying solely on cut-and-choose techniques for verified delegated quantum computation cannot achieve both security and efficiency simultaneously, highlighting the need for alternative methods.

Contribution

The authors prove the fundamental limitations of cut-and-choose techniques in achieving secure and efficient verification in delegated quantum computation.

Findings

Cut-and-choose alone cannot ensure both security and efficiency.

Additional techniques are necessary for practical verifiable quantum computation.

Pure cut-and-choose protocols are fundamentally limited in this setting.

Abstract

Delegated quantum computation enables a client with limited quantum capabilities to outsource computations to a more powerful quantum server while preserving correctness and privacy. Verification is crucial in this setting to ensure that the untrusted quantum server performs the computation honestly and returns correct results. A common verification method is the quantum cut-and-choose technique. Inspired by classical verification methods for two-party computation, the client uses the majority of the delegated rounds to test the server's honesty, while keeping the remaining ones for the actual computation. Combining this technique with other methods, such as quantum error correction, could help achieve negligible cheating probabilities for the server; however, such methods can impose significant overheads making implementations unfeasible for the near-term future. In this work, we investigate whether cut-and-choose can yield efficient and secure verifiable quantum computation without additional costly techniques. We find that verifiable delegated quantum computation protocols relying solely on cut-and-choose techniques cannot be secure and efficient at the same time.