Cross-Platform Verification of Intermediate Scale Quantum Devices

Abstract

We describe a protocol for cross-platform verification of quantum simulators and quantum computers. We show how to measure directly the overlap $\text{Tr}\left[{\rho }_1{\rho }_2\right]$ and the purities $\text{Tr}\left[{\rho }_{1,2}^2\right]$, and thus a fidelity of two possibly mixed quantum states ${\rho }_1$ and ${\rho }_2$ prepared in separate experimental platforms. We require only local measurements in randomized product bases, which are communicated classically. As a proof-of-principle, we present the measurement of experiment-theory fidelities for entangled $10$-qubit quantum states in a trapped ion quantum simulator.