Protected quantum computation with multiple resonators in ultrastrong coupling circuit QED

TL;DR

This paper proposes a method for protected quantum computation using multiple resonators in ultrastrong coupling circuit QED, demonstrating improved coherence and fidelity through theoretical analysis of noise and entangled ground states.

Contribution

It introduces a scheme for quantum gates with multiple resonators in ultrastrong coupling circuit QED, leveraging entangled ground states to enhance qubit coherence and operation fidelity.

Findings

Coherence time and fidelity are significantly improved in the ultrastrong coupling regime.

Ground state is an entangled photonic 'cat' state.

Optimal noise conditions enhance quantum operation robustness.

Abstract

We investigate theoretically the dynamical behavior of a qubit obtained with the two ground eigenstates of an ultrastrong coupling circuit-QED system consisting of a finite number of Josephson fluxonium atoms inductively coupled to a transmission line resonator. We show an universal set of quantum gates by using multiple transmission line resonators (each resonator represents a single qubit). We discuss the intrinsic 'anisotropic' nature of noise sources for fluxonium artificial atoms. Through a master equation treatment with colored noise and manylevel dynamics, we prove that, for a general class of anisotropic noise sources, the coherence time of the qubit and the fidelity of the quantum operations can be dramatically improved in an optimal regime of ultrastrong coupling, where the ground state is an entangled photonic 'cat' state.