Cross-Verification of Independent Quantum Devices

C Greganti,P Schindler,J F Fitzsimons,T F Demarie,T Monz,R Stricker,M Meth,R Blatt,L A Rozema,P Walther,I Alonso Calafell,A Erhard,J A Jones,V Saggio,M Ringbauer,L Postler

doi:10.1103/physrevx.11.031049

Abstract

Quantum computers are on the brink of surpassing the capabilities of even the most powerful classical computers. This naturally raises the question of how one can trust the results of a quantum computer when they cannot be compared to classical simulation. Here we present a verification technique that exploits the principles of measurement-based quantum computation to link quantum circuits of different input size, depth, and structure. Our approach enables consistency checks of quantum computations within a device, as well as between independent devices. We showcase our protocol by applying it to five state-of-the-art quantum processors, based on four distinct physical architectures: nuclear magnetic resonance, superconducting circuits, trapped ions, and photonics, with up to 6 qubits and 200 distinct circuits.

Highlights

Quantum computers represent a fundamental shift in the way we think about computation
Quantum computers are on the brink of surpassing the capabilities of even the most powerful classical computers, which naturally raises the question of how one can trust the results of a quantum computer when they cannot be compared to classical simulation Here, we present a cross-verification technique that exploits the principles of measurement-based quantum computation to link quantum circuits of different input size, depth, and structure
While our approach does not aim to solve the full problem of verification that is secure against any dishonest behavior of the devices, it enables us to build a high level of trust in the outputs of honest quantum devices by observing the measurement-based quantum computation (MBQC) relationships upheld when sampling from different realizations of seemingly unrelated circuits. We demonstrate this technique by running up to 200 distinct circuits of different width and depth on five stateof-the-art quantum processors, using four primary technologies for digital quantum computation: (1) a nuclear magnetic resonance (NMR) device [7] at the University of Oxford, (2) cloud-accessible superconducting systems from IBM [31] and Rigetti [32], (3) a trapped-ion quantum processor [8] at the University of Innsbruck, and (4) a photonic cluster-state quantum device [33] at the University of Vienna

Summary

Introduction

Quantum computers represent a fundamental shift in the way we think about computation. By harnessing quantum interference effects between different possible branches of a computation, quantum processors have the potential to drastically outperform conventional computers for a range of tasks [1,2,3,4,5,6]. Potential applications of quantum computation range from cryptanalysis to the simulation of physical systems, and even to machine learning. Extraordinary experimental efforts in recent years have enabled demonstrations of the technology’s potential in a growing number of physical systems [7,8,9,10]. For certain simulation [11,12] and sampling [13] tasks, these devices are already pushing the limits of classical supercomputers, and it is foreseeable that the generation of quantum processors will vastly outperform their classical counterparts

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