Fig. 3: Randomized benchmarking with a calibrated beamsplitter pulse.
From: High-fidelity parametric beamsplitting with a parity-protected converter
a Wigner function of Bob after preparing \(\left|{0}_{a}{1}_{b}\right\rangle\) and implementing 1, 10 and 60 calibrated swaps. Each swap is a combination of two identical beamplitter pulses. b Probability of ending in the target state \(\left|{0}_{a}{1}_{b}\right\rangle\) after executing the RB protocol with randomly selected gates from GDR (yellow circles). The curve is normalized to account for state preparation and readout imperfections (Supplementary Note 10), and is in good agreement with a single-exponential, with a decay constant of τRB = 1271 ± 4 gates. This `Raw RB' is practically indistinguishable from the sequences post-selected on the coupler ground state (black crosses), with the difference of the two curves shown below the main plot (pink crosses). c Focusing on the first 2250 gates, we use measurements of both cavities to post-select on sequences in which no photon loss event occurred (green diamonds). We compare these sequences to the raw RB in (b) (yellow), showing an improvement in average gate infidelity from 0.078 ± 0.001% to 0.020 ± 0.001%. d The gate-sets required for the above protocols are generated from calibrated beampslitter pulses with tanh-shaped ramps, where different UBS(φ) are obtained by changing the relative phase of our drives. e The benchmarking sequences consist of randomly generated pulses that, under ideal operation, map \(\left|{0}_{a}{1}_{b}\right\rangle\) back to itself. After each sequence, we measure whether the coupler is in its ground state, the presence of a photon in Bob, and the presence of a photon in Alice using an additional swap gate. This lets us generate the raw, coupler-selected and leakage-detected RB datasets. All sequences are also conditioned on Bob’s ancilla ending in its ground state, to discount first-order effects of ancilla heating.
