Protected qubit based on a superconducting current mirror

TL;DR

This paper introduces a protected superconducting qubit using exciton condensation in coupled Josephson junction chains, with exponential error suppression for most gates, advancing fault-tolerant quantum computing.

Contribution

It presents a novel qubit design based on exciton condensation that offers exponential suppression of errors and a universal set of fault-tolerant quantum gates.

Findings

All unwanted Hamiltonian terms are exponentially suppressed with chain length.

Most quantum gates in the scheme offer exponential error suppression.

A single non-fault-tolerant gate requires about 50% precision, assuming others are exact.

Abstract

We propose a qubit implementation based on exciton condensation in capacitively coupled Josephson junction chains. The qubit is protected in the sense that all unwanted terms in its effective Hamiltonian are exponentially suppressed as the chain length increases. We also describe an implementation of a universal set of quantum gates. Most gates also offer exponential error suppression. The only gate that is not intrinsically fault-tolerant needs to be realized with about 50% precision, provided the other gates are exact.