Two-electron spin correlations in precision placed donors in silicon

M A Broome,C D Hill,M G House,M Y Simmons,W J Baker,T F Watson,J G Keizer,S K Gorman,L C L Hollenberg,D Keith,S J Hile

doi:10.1038/s41467-018-02982-x

M A Broome, C D Hill + Show 9 more

Open Access

https://doi.org/10.1038/s41467-018-02982-x

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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 ± 1 nm. By utilising 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.

Highlights

Substitutional donor atoms in silicon are promising qubits for quantum computation with extremely long relaxation and dephasing times demonstrated
While the first two protocols require the use of high frequency microwave fields for electron spin resonance[11], a direct two-electron SWAP necessitates the ability to turn on and off the exchange interaction between the electrons over orders of magnitude for high fidelity two-qubit operations
We have demonstrated a controllable exchange interaction resulting in two-electron spin anti-correlations on precision placed 2P−1P donors qubits in Si using in-plane ‘detuning’ gates

Summary

Introduction

Substitutional donor atoms in silicon are promising qubits for quantum computation with extremely long relaxation and dephasing times demonstrated. While the extent of a single donor wavefunction is well understood[12,13,14], modelling the exchange coupling between two donor electrons is more complex[12,13,14,15,16,17] due to multi-valley interference effects[18] To this end, a critical challenge for donor-based architectures is to know the distance required between the donors in order to turn the exchange interaction on and off with external gates[15,16]. By observing the onset of these anti-correlated spin states as a function of detuning pulse voltage and time, we estimate the magnitude of tunnel coupling between the two donor qubits, and provide a roadmap towards coherent exchange gates for future devices

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