Benchmark

The goal of benchmarking is to determine how far the output of a noisy system is from its ideal behavior; this becomes exceedingly difficult for large quantum systems where classical simulations become intractable. A common approach is to turn to circuits comprised of elements of the Clifford group (e.g., CZ, CNOT, π and π/2 gates), which probe quantum behavior but are nevertheless efficient to simulate classically. However, there is some concern that these circuits may overlook error sources that impact the larger Hilbert space. In this manuscript, we show that for a broad class of error models these concerns are unwarranted. In particular, we show that, for error models that admit noise tailoring by Pauli twirling, the diamond norm and fidelity of any generic circuit is well approximated by the fidelities of proxy circuits composed only of Clifford gates. We discuss methods for extracting the fidelities of these Clifford proxy circuits in a manner that is robust to errors in state preparation and measurement and demonstrate these methods in simulation and on IBM Quantum’s fleet of deployed heron devices. ...

We introduce a volumetric benchmark for near-term quantum platforms based on the generation and verification of genuine entanglement across n-qubits using graph states and direct stabilizer measurements. Our benchmark evaluates the robustness of multipartite and bipartite n-qubit entanglement with respect to many sources of hardware noise: qubit decoherence, CNOT and swap gate noise, and readout error. We demonstrate our benchmark on multiple superconducting qubit platforms available from IBM (ibmq_belem, ibmq_toronto, ibmq_guadalupe and ibmq_jakarta). Subsets of n<10 qubits are used for graph state preparation and stabilizer measurement. Evaluation of genuine and biseparable entanglement witnesses we report observations of 5 qubit genuine entanglement, but robust multipartite entanglement is difficult to generate for n>4 qubits and identify two-qubit gate noise as strongly correlated with the quality of genuine multipartite entanglement. ...