Exchange coupling in silicon quantum dots: Theoretical considerations for quantum computation

TL;DR

This paper analyzes exchange coupling in silicon double quantum dots for spin qubits, exploring two schemes and their sensitivity to charge noise using theoretical models to identify optimal operational conditions.

Contribution

It provides a detailed theoretical comparison of two spin qubit schemes in silicon quantum dots and investigates conditions for minimizing charge noise effects.

Findings

Different exchange dependencies in two qubit schemes

Identification of optimal spots with minimal charge noise influence

Theoretical framework for system sensitivity analysis

Abstract

We study exchange coupling in Si double quantum dots, which have been proposed as suitable candidates for spin qubits due to their long spin coherence times. We discuss in detail two alternative schemes which have been proposed for implementing spin qubits in quantum dots. One scheme uses spin states in a single dot and the interdot exchange coupling controls interactions between unbiased dots. The other scheme employs the singlet and triplet states of a biased double dot as the two-level system making up the qubit and exchange controls the energy splitting of the levels. Exchange in these two configurations depends differently on system parameters. Our work relies on the Heitler-London approximation and the Hund-Mulliken molecular orbital method. The results we obtain enable us to investigate the sensitivity of the system to background charge fluctuations and determine the conditions under which optimal spots, at which the influence of the charge noise is minimized, may exist in Si double quantum dot structures.