Coherent control of a donor-molecule electron spin qubit in silicon

Donor spins in silicon provide a promising material platform for large scale quantum computing. Excellent electron spin coherence times of T-2(*) = 268 mu s with fidelities of 99.9% have been demonstrated for isolated phosphorus donors in isotopically pure Si-28, where donors are local-area-implanted in a nanoscale MOS device. Despite robust single qubit gates, realising two-qubit exchange gates using this technique is challenging due to the statistical nature of the dopant implant and placement process. In parallel a precision scanning probe lithography route has been developed to place single donors and donor molecules on one atomic plane of silicon with high accuracy aligned to heavily phosphorus doped silicon in-plane gates. Recent results using this technique have demonstrated a fast (0.8 ns) two-qubit gate with two P donor molecules placed 13 nm apart in Si-nat. In this paper we demonstrate a single qubit gate with coherent oscillations of the electron spin on a P donor molecule in Si-nat patterned by scanning tunneling microscope (STM) lithography. The electron spin exhibits excellent coherence properties, with a T-2 decoherence time of 298 +/- 30 mu s, and T-2(*) dephasing time of 295 +/- 23 ns.