Quantum noise in the Josephson charge qubit

TL;DR

This paper investigates the decoherence mechanisms in Josephson charge qubits, revealing that quantum noise-induced spontaneous emission is the main cause of energy relaxation, with noise spectral density proportional to qubit energy.

Contribution

It provides experimental measurements of decoherence and identifies quantum noise as the primary relaxation process in Josephson charge qubits.

Findings

Spontaneous emission dominates energy relaxation.

Noise spectral density scales with qubit excitation energy.

High-frequency quantum noise impacts qubit coherence.

Abstract

We study decoherence of the Josephson charge qubit by measuring energy relaxation and dephasing with help of the single-shot readout. We found that the dominant energy relaxation process is a spontaneous emission induced by quantum noise coupled to the charge degree of freedom. Spectral density of the noise at high frequencies is roughly proportional to the qubit excitation energy.