Two-Electron Spin Correlations in Precision Placed Donors in Silicon

TL;DR

This paper demonstrates precise control and measurement of two-electron spin states in silicon donor qubits, showing tunable exchange interactions and providing insights for scalable quantum computing architectures.

Contribution

It introduces a method using scanning tunnelling microscopy lithography to precisely place donors and control their spin interactions in silicon quantum devices.

Findings

Measured anti-correlated spin states at 16 nm separation.

Achieved electrical control of exchange interaction.

Determined tunnel coupling to be 200 MHz.

Abstract

Substitutional donor atoms in silicon are promising qubits for quantum computation with extremely long relaxation and dephasing times demonstrated. One of the critical challenges of scaling these systems is determining inter-donor distances to achieve controllable wavefunction overlap while at the same time performing high fidelity spin readout on each qubit. Here we achieve such a device by means of scanning tunnelling microscopy lithography. We measure anti-correlated spin states between two donor-based spin qubits in silicon separated by 16${\pm}1$ nm. By utilizing an asymmetric system with two phosphorus donors at one qubit site and one on the other (2P-1P), we demonstrate that the exchange interaction can be turned on and off via electrical control of two in-plane phosphorus doped detuning gates. We determine the tunnel coupling between the 2P-1P system to be 200 MHz and provide a roadmap for the observation of two-electron coherent exchange oscillations.