We consider charge qubits based on shallow donor electron states in silicon and coupled quantum dots in GaAs. Specifically, we study the feasibility of P2+ 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 P2+ 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:P2+ and GaAs double quantum dot quantum computer architectures.
@article{arxiv.cond-mat/0412340,
title = {Charge qubits in semiconductor quantum computer architectures: Tunnel coupling and decoherence},
author = {Xuedong Hu and Belita Koiller and S. Das Sarma},
journal= {arXiv preprint arXiv:cond-mat/0412340},
year = {2009}
}