Conditional quantum operation of two exchange-coupled single-donor spin qubits in a MOS-compatible silicon device

TL;DR

This paper demonstrates a coherent, conditional control of two exchange-coupled $^{31}$P donor electron spins in silicon, achieving precise coupling measurement and a scalable two-qubit gate compatible with existing silicon fabrication methods.

Contribution

It introduces a method for conditional quantum control of donor spins in silicon with precise exchange coupling measurement, enabling scalable quantum computing architectures.

Findings

Measured exchange coupling with unprecedented precision.

Achieved a native two-qubit Controlled-Rotation gate.

Scheme is insensitive to variations in coupling strength.

Abstract

Silicon nanoelectronic devices can host single-qubit quantum logic operations with fidelity better than 99.9%. For the spins of an electron bound to a single donor atom, introduced in the silicon by ion implantation, the quantum information can be stored for nearly 1 second. However, manufacturing a scalable quantum processor with this method is considered challenging, because of the exponential sensitivity of the exchange interaction that mediates the coupling between the qubits. Here we demonstrate the conditional, coherent control of an electron spin qubit in an exchange-coupled pair of $^{31}$P donors implanted in silicon. The coupling strength, $J = 32.06 \pm 0.06$ MHz, is measured spectroscopically with unprecedented precision. Since the coupling is weaker than the electron-nuclear hyperfine coupling $A \approx 90$ MHz which detunes the two electrons, a native two-qubit Controlled-Rotation gate can be obtained via a simple electron spin resonance pulse. This scheme is insensitive to the precise value of $J$, which makes it suitable for the scale-up of donor-based quantum computers in silicon that exploit the Metal-Oxide-Semiconductor fabrication protocols commonly used in the classical electronics industry.