Charge qubits in semiconductor quantum computer architectures: Tunnel coupling and decoherence

TL;DR

This paper investigates charge qubits in silicon and GaAs, analyzing tunnel coupling and decoherence, with a focus on silicon's multi-valley effects and their impact on qubit performance.

Contribution

It provides a detailed analysis of P$_2^+$ charge qubits in silicon, highlighting the effects of valley interference on tunnel coupling and comparing silicon and GaAs architectures.

Findings

Valley interference causes tunnel coupling to center around zero.

Silicon bandstructure has minimal impact on electron-phonon decoherence.

Comparison shows differences in qubit properties between Si:P$_2^+$ and GaAs quantum dots.

Abstract

We consider charge qubits based on shallow donor electron states in silicon and coupled quantum dots in GaAs. Specifically, we study the feasibility of P$_2^+$ charge qubits in Si, focusing on single qubit properties in terms of tunnel coupling between the two phosphorus donors and qubit decoherence caused by electron-phonon interaction. By taking into consideration the multi-valley structure of the Si conduction band, we show that inter-valley quantum interference has important consequences for single-qubit operations of P$_2^+$ charge qubits. In particular, the valley interference leads to a tunnel-coupling strength distribution centered around zero. On the other hand, we find that the Si bandstructure does not dramatically affect the electron-phonon coupling and consequently, qubit coherence. We also critically compare charge qubit properties for Si:P$_2^+$ and GaAs double quantum dot quantum computer architectures.