Tomography of entangling two-qubit logic operations in exchange-coupled donor electron spin qubits

TL;DR

This paper demonstrates high-fidelity universal quantum gates and entanglement in silicon donor electron spins, showing their potential for scalable quantum computing with preserved coherence.

Contribution

It provides the first experimental realization and tomography of entangling two-qubit gates in exchange-coupled donor electron spins in silicon.

Findings

Achieved ~93% fidelity in creating Bell states

Observed exchange interaction does not affect qubit coherence

Demonstrated universal quantum gates in silicon donor system

Abstract

Scalable quantum processors require high-fidelity universal quantum logic operations in a manufacturable physical platform. Donors in silicon provide atomic size, excellent quantum coherence and compatibility with standard semiconductor processing, but no entanglement between donor-bound electron spins has been demonstrated to date. Here we present the experimental demonstration and tomography of universal 1- and 2-qubit gates in a system of two weakly exchange-coupled electrons, bound to single phosphorus donors introduced in silicon by ion implantation. We surprisingly observe that the exchange interaction has no effect on the qubit coherence. We quantify the fidelity of the quantum operations using gate set tomography (GST), and we use the universal gate set to create entangled Bell states of the electrons spins, with fidelity ~ 93%, and concurrence 0.91 +/- 0.08. These results form the necessary basis for scaling up donor-based quantum computers.