Sound certification of memory-bounded quantum computers

TL;DR

This paper presents a practical, sound certification protocol for quantum gates in memory-bounded quantum computers, eliminating the need for trusted state preparation and measurement, and validated through numerical experiments.

Contribution

It introduces quantum system quizzing, a novel certification method that is sound, robust, and does not rely on trusted state preparation, suitable for memory-limited quantum devices.

Findings

Proved soundness for a wide range of gate sets including universal gates.

Resolved tensor product structure recovery in memory-bounded systems.

Validated efficiency and robustness through numerical experiments.

Abstract

The rapid advancement of quantum hardware calls for the development of reliable methods to certify its correct functioning. However, existing certification tests often fall short: they either rely on flawless state preparation and measurement or lack soundness guarantees, meaning that they do not rule out incorrect implementations of the target operations by a quantum device. We introduce an approach, which we call quantum system quizzing, for the certification of quantum gates in a practical server-user scenario, where a classical user tests the results of quantum computation performed by a quantum server by checking its responses to a set of predesigned small-sized computational problems. Importantly, this approach does not require trusted state preparation and measurement and is thus inherently free from the associated systematic errors. For a wide range of relevant gate sets, including a universal one, we prove our certification protocol to be sound; i.e., it is guaranteed to reject any incorrect gate implementation, under the assumptions of a known Hilbert space dimension and context independence of error. A major technical challenge that we are first to resolve is recovering the tensor product structure of a multi-qubit system in the memory-bounded single-device setup. Finally, we prove the robustness of our protocol and validate its sample and computational efficiency through extensive numerical experiments. Our protocol is platform-agnostic and introduces a new paradigm for benchmarking and comparing diverse quantum architectures.