Fig. 1: Overview of the protocol.
From: Certified randomness using a trapped-ion quantum processor
a, The idealized protocol. A client submits M random circuits \({\{{C}_{i}\}}_{i\in [M]}\) serially to a randomness server and expects bitstrings \({\{{x}_{i}\}}_{i\in [M]}\) back, each within a time tQC. b, A subset of circuit-bitstring pairs is used to compute the XEB score. The XEB score has distributions (bottom plot for qualitative illustration only) corresponding to either an honest server or an adversarial server performing a low-fidelity classical simulation. For any XEB target indicated by the dashed line, an honest server may fail to achieve a score above this threshold with a probability Pfail. c, Illustration of the challenge circuits, consisting of layers of UZZ gates sandwiched between layers of random SU(2) gates on all qubits. The arrangement of two-qubit gates is obtained via edge colouring (right) on a random n-node graph. d, Client-server interaction as implemented in our protocol. Following a device-readiness check (‘precheck’), the client submits a batch of 2b circuits and expects all the samples corresponding to the batch to be returned within a cutoff duration Tb,cutoff. Note that only one batch with execution time Tbatch is illustrated in the figure. The client continues the protocol until M total circuits have been successfully executed.
