Simulation of Si:P spin-based quantum computer architecture

TL;DR

This paper presents a detailed simulation of phosphorus donor interactions in silicon quantum wells, analyzing effects of confinement, gate voltages, and donor positioning to inform the design of silicon-based quantum computers.

Contribution

It introduces a comprehensive simulation framework for donor-based silicon quantum computers, incorporating a two-valley model and unrestricted Hartree-Fock methods for realistic device analysis.

Findings

Quantum well confinement shrinks charge distribution in all dimensions.

Gate voltages influence exchange oscillations and gate fidelity.

Donor positioning significantly affects exchange interactions and oscillation suppression.

Abstract

We present a systematic and realistic simulation for single and double phosphorous donors in a silicon-based quantum computer design. A two-valley equation is developed to describe the ground state of phosphorous donors in strained silicon quantum well (QW), with the central cell effect treated by a model impurity potential. We find that the increase of quantum well confinement leads to shrinking charge distribution in all 3 dimensions. Using an unrestricted Hartree-Fock method with Generalized Valence Bond (GVB) single-particle wave functions, we are able to solve the two-electron Sch${\ddot o}$dinger equation with quantum well confinement and realistic gate potentials. The effects of QW width, gate voltages, donor separation, and donor position are calculated and analyzed. The gate tunability and gate fidelity are defined and evaluated, for a typical QC design. Estimates are obtained for the duration of $\sqrt{SWAP}$ gate operation and the required accuracy in voltage control. A strong exchange oscillation is observed as both donors are shifted along [001] axis but with their separation unchanged. Applying a gate potential tends to suppress the oscillation. The exchange oscillation as a function of donor position along [100] axis is found to be completely suppressed as the donor separation is decreased. The simulation presented in this paper is of importance to the practical design of an exchange-based silicon quantum computer.