Engineering inter-qubit exchange coupling between donor bound electrons in silicon

TL;DR

This paper explores electrical control of exchange coupling between donor electrons in silicon, demonstrating a tunable, robust method for two-qubit gates in silicon quantum computing with reduced fabrication constraints.

Contribution

It introduces a detuning gate design for donor qubits that achieves large exchange tunability and mitigates oscillations, improving upon previous barrier gate methods.

Findings

Achieved five orders of magnitude change in exchange energy with modest electric fields.

Demonstrated reduced sensitivity to donor placement and fabrication imperfections.

Provided state-of-the-art calculations of exchange energies for 1P-1P and 2P-1P donor systems.

Abstract

We investigate the electrical control of the exchange coupling (J) between donor bound electrons in silicon with a detuning gate bias, crucial for the implementation of the two-qubit gate in a silicon quantum computer. We find the asymmetric 2P-1P system provides a highly tunable exchange-curve with mitigated J-oscillation, in which 5 orders of magnitude change in the exchange energy can be achieved using a modest range of electric field for 15 nm qubit separation. Compared to the barrier gate control of exchange in the Kane qubit, the detuning gate design reduces the demanding constraints of precise donor separation, gate width, density and location, as a range of J spanning over a few orders of magnitude can be engineered for various donor separations. We have combined a large-scale full band atomistic tight-binding method with a full configuration interaction technique to capture the full two-electron spectrum of gated donors, providing state-of-the-art calculations of exchange energy in 1P-1P and 2P-1P qubits.