Cross-Platform Comparison of Arbitrary Quantum Processes

In this work, we present a protocol for comparing the performance of arbitrary quantum processes executed on spatially or temporally disparate quantum platforms using Local Operations and Classical Communication (LOCC). The protocol involves sampling local unitary operators, which are then communicated to each platform via classical communication to construct quantum state preparation and measurement circuits. Subsequently, the local unitary operators are implemented on each platform, resulting in the generation of probability distributions of measurement outcomes. The max process fidelity is estimated from the probability distributions, which ultimately quantifies the relative performance of the quantum processes. Furthermore, we demonstrate that this protocol can be adapted for quantum process tomography. We apply the protocol to compare the performance of five quantum devices from IBM and the "Qianshi" quantum computer from Baidu via the cloud. Remarkably, the experimental results reveal that the protocol can accurately compare the performance of the quantum processes implemented on different quantum computers, requiring significantly fewer measurements than those needed for full quantum process tomography. We view our work as a catalyst for collaborative efforts in cross-platform comparison of quantum computers.