Decoherence and gate performance of coupled solid state qubits

TL;DR

This paper analyzes how coupled solid state qubits perform under decoherence, showing that common bath coupling can optimize gate fidelity at low temperatures, especially for CPHASE gates, due to commuting interactions.

Contribution

It demonstrates that low-temperature operation with common baths enhances gate performance for solid state qubits with  type of coupling, highlighting advantages over other coupling schemes.

Findings

Uncorrelated baths degrade gate quality more at low temperatures.

Common bath coupling allows for optimal gate performance at low temperatures.

Coupling that commutes with decoherence interactions improves gate fidelity.

Abstract

Solid state quantum bits are promising candidates for the realization of a {\em scalable} quantum computer. However, they are usually strongly limited by decoherence due to the many extra degrees of freedom of a solid state system. We investigate a system of two solid state qubits that are coupled via $\sigma_z^{(i)} \otimes \sigma_z^{(j)}$ type of coupling. This kind of setup is typical for {\em pseudospin} solid-state quantum bits such as charge or flux systems. We evaluate decoherence properties and gate quality factors in the presence of a common and two uncorrelated baths coupling to $\sigma_z$, respectively. We show that at low temperatures, uncorrelated baths do degrade the gate quality more severely. In particular, we show that in the case of a common bath, optimum gate performance of a CPHASE gate can be reached at very low temperatures, because our type of coupling commutes with the coupling to the decoherence, which makes this type of coupling attractive as compared to previously studied proposals with $\sigma_y^{(i)} \otimes \sigma_y^{(j)}$ -coupling. Although less pronounced, this advantage also applies to the CNOT gate.