Dephasing due to background charge fluctuations

TL;DR

This paper investigates how background charge fluctuations cause dephasing in charge qubits, deriving dephasing rates for different coupling scenarios and comparing them with existing models.

Contribution

It provides a detailed analysis of dephasing mechanisms due to background charge noise, including the effects of fluctuating tunnel coupling and bias, using stochastic differential equations.

Findings

Dephasing rate inversely proportional to telegraph noise time constant in strong coupling.

Gaussian decay observed in initial dephasing regime with tunnel coupling fluctuations.

Dephasing rate matches spectral weight predictions in weak coupling bias fluctuations.

Abstract

In quantum computation, quantum coherence must be maintained during gate operation. However, in physical implementations, various couplings with the environment are unavoidable and can lead to a dephasing of a quantum bit(qubit). The background charge fluctuations are an important dephasing process, especially in a charge qubit system. We examined the dephasing rate of a qubit due to random telegraph noise. Solving stochastic differential equations, we obtained the dephasing rate of a qubit constructed of a coupled-dot system; we applied our results to the charge Josephson qubit system. We examined the dephasing rates due to two types of couplings between the coupled-dot system and the background charge, namely, fluctuation in the tunnel coupling constant and fluctuation in the asymmetric bias. For a strong coupling condition, the dephasing rate was inversely proportional to the time constant of the telegraph noise. When there is fluctuation in the tunnel coupling constant, Gaussian decay occurs in the initial regime. We also examined the rate of dephasing due to many impurity sites. For a weak coupling condition with fluctuation in the asymmetric bias, the obtained dephasing rate coincided with that obtained by the perturbation method using the spectral weight of a boson thermal bath, which is proportional to the inverse of the frequency.