We analyze the accuracy of quantum phase gates acting on "0-π qubits" in superconducting circuits, where the gates are protected against thermal and Hamiltonian noise by continuous-variable quantum error-correcting codes. The gates are executed by turning on and off a tunable Josephson coupling between an LC oscillator and a qubit or pair of quits; assuming perfect qubits, we show that the gate errors are exponentially small when the oscillator's impedance L/C is large compared to ℏ/4e2≈1kΩ. The protected gates are not computationally universal by themselves, but a scheme for universal fault-tolerant quantum computation can be constructed by combining them with unprotected noisy operations. We validate our analytic arguments with numerical simulations.
@article{arxiv.1302.4122,
title = {Protected gates for superconducting qubits},
author = {Peter Brooks and Alexei Kitaev and John Preskill},
journal= {arXiv preprint arXiv:1302.4122},
year = {2020}
}