Noise and the Measurement Process for a Circular Josephson Array Qubit

TL;DR

This paper analyzes a circular Josephson array charge qubit, focusing on how noise affects its coherence and measurement process, and estimates decoherence from different noise sources using the spin-boson model.

Contribution

It introduces a model for a circular Josephson array qubit with long relaxation times and simulates the measurement process considering noise effects.

Findings

Decoherence due to ohmic and 1/f noise estimated

Long relaxation times achievable in the proposed qubit

Measurement process modeled with density matrix simulation

Abstract

We discuss a charge qubit consisting of a circular array of Josephson junctions. The two-level system we consider couples the two charge states through a higher order tunneling process thus making it possible to achieve a long relaxation time. Using the spin-boson Hamiltonian, we estimate decoherence due to ohmic as well as 1/f noise. We simulate the quantum mechanical measurement process by studing the density matrix of the qubit and a capacitively coupled single-electron transistor that measures the charge.