Silicon quantum computation based on magnetic dipolar coupling (6 pages)

Zhongxiang Han, Yun‐Feng Xiao, Guang‐Can Guo

Andrei Derevianko, Caleb C. Cannon

Rogério de Sousa, J. D. Delgado, S. Das Sarma

A dipolar gate alternative to the exchange-gate-based Kane quantum computer is proposed where the qubits are electron spins of shallow group V donors in silicon. Residual exchange coupling is treated as gate error amenable to quantum error correction, removing the stringent requirements on donor positioning characteristic of all silicon exchange-based implementations [Koiller et al., Phys. Rev. Lett. 88, 027903 (2002)]. Contrary to common speculation, such a scheme is scalable with no overhead in gating time even though it is based on long-range dipolar interqubit coupling.

Brage Golding, M. I. Dykman

A solid-state quantum computer with dipolar coupling between qubits is proposed. The qubits are formed by the low-lying states of an isolated acceptor in silicon. The system has the scalability inherent to spin-based solid state systems, but the spatial separation between the qubits is an order of magnitude larger. Despite strong dipolar inter-qubit coupling, the decoherence rate, as measured by electric dipolar echoes at an energy splitting of 1.5 GHz, is less than 1 kHz at low temperatures. For inter-acceptor distances of 100 nm and for modest microwave field amplitudes (50 V/cm) the clock frequency of the quantum computer is 0.1 GHz, which yields a quality factor of 105. This paper describes ideas for detection and operation of the quantum computer, and examines limitations imposed by noise sources.

J. R. Petta

Ian Thorvaldson, P. Macha, Jan-Michael Reiner +13 more

ABSTRACT Nuclear spins have been studied since the beginning of quantum information science since they form the prototypical qubit with long coherence times and high‐fidelity operation. To perform practical fault‐tolerant quantum computations, however, not only do we require precision manufacturing techniques to produce millions of qubits, but these techniques need to consistently yield low‐error qubits. A deep understanding and control of the interactions between the qubits and their environment are needed as we scale so that devices can be engineered to avoid high error rates. In this work, we experimentally and theoretically characterize two often‐overlooked error mechanisms affecting nuclear spin qubits in silicon caused by local interactions. The first is the direct magnetic interactions between nuclear spins, causing dipolar coupling errors, and the second is the interactions between the nuclear spins and their associated electron spin, causing “hotspots” of anisotropic hyperfine coupling errors. By modeling the properties of the combined electron–nuclear spin system as a function of magnetic field, contact hyperfine strength, and electron tunnel rate, we show how these errors can be reliably mitigated, giving rise to readout fidelities of .