We introduce simple qubit-encodings and logic gates which eliminate the need for certain difficult single-qubit operations in superconducting phase-qubits, while preserving universality. The simplest encoding uses two physical qubits per logical qubit. Two architectures for its implementation are proposed: one employing N physical qubits out of which N/2 are ancillas fixed in the |1> state, the other employing N/2+1 physical qubits, one of which is a bus qubit connected to all others. Details of a minimal set of universal encoded logic operations are given, together with recoupling schemes, that require nanosecond pulses. A generalization to codes with higher ratio of number of logical qubits per physical qubits is presented. Compatible decoherence and noise suppression strategies are also discussed.
@article{arxiv.cond-mat/0204153,
title = {Quantum Codes for Simplifying Design and Suppressing Decoherence in Superconducting Phase-Qubits},
author = {Daniel A. Lidar and Lian-Ao Wu and Alexandre Blais},
journal= {arXiv preprint arXiv:cond-mat/0204153},
year = {2016}
}