Decoherence in qubits due to low-frequency noise

TL;DR

This paper reviews the theory of qubit decoherence caused by low-frequency 1/f noise from two-state fluctuators, highlighting non-Gaussian effects and analyzing the impact on quantum coherence and manipulation protocols.

Contribution

It introduces a realistic spin-fluctuator model to evaluate qubit dynamics, including non-Gaussian noise effects, and extends analysis to systems with many fluctuators causing 1/f noise.

Findings

Non-Gaussian noise significantly affects qubit coherence.

Exact solutions for single fluctuator interactions are obtained.

Analysis of experimental data suggests non-Gaussian behavior in Josephson qubits.

Abstract

The efficiency of the future devices for quantum information processing is limited mostly by the finite decoherence rates of the qubits. Recently a substantial progress was achieved in enhancing the time, which a solid-state qubit demonstrates a coherent dynamics. This progress is based mostly on a successful isolation of the qubits from external decoherence sources. Under these conditions the material-inherent sources of noise start to play a crucial role. In most cases the noise that quantum device demonstrate has 1/f spectrum. This suggests that the environment that destroys the phase coherence of the qubit can be thought of as a system of two-state fluctuators, which experience random hops between their states. In this short review we discuss the current state of the theory of the decoherence due to the qubit interaction with the fluctuators. We describe the effect of such an environment on different protocols of the qubit manipulations - free induction and echo signal. It turns out that in many important cases the noise produced by the fluctuators is non-Gaussian. Consequently the results of the interaction of the qubit with the fluctuators are not determined by the pair correlation function only. We describe the effect of the fluctuators using so-called spin-fluctuator model. Being quite realistic this model allows one to evaluate the qubit dynamics in the presence of one fluctuator exactly. This solution is found, and its features, including non-Gaussian effects are analyzed in details. We extend this consideration for the systems of large number of fluctuators, which interact with the qubit and lead to the 1/f noise. We discuss existing experiments on the Josephson qubit manipulation and try to identify non-Gaussian behavior.