How to verify proof of Quantumness of a Quantum System available over the cloud

A Reddit user seeks methods to verify a cloud-based quantum system’s authenticity, questioning whether it’s a true quantum computer or a simulator, and how to confirm its claimed 70 logical qubits and 2M+ gate depth. Standard benchmarks like quantum volume or randomized benchmarking could distinguish hardware from simulators by exposing noise patterns unique to physical qubits, though simulators may mimic small-scale results. Algorithms like quantum supremacy circuits (e.g., Google’s 2019 cross-entropy test) or boson sampling could stress-test the system’s qubit count and gate fidelity, revealing hardware limitations a simulator might hide. For gate depth validation, deep variational algorithms (e.g., QAOA with high p-values) or error mitigation tests would probe the system’s ability to sustain long computations without decoherence or crosstalk. Public frameworks (Qiskit, Cirq) offer pre-built tools like Quantum Characterisation, Verification, and Validation (QCVV) protocols, but independent audits remain critical for unproven cloud-based quantum claims.