Preprint: Spin-valley lifetimes in a silicon quantum dot with tunable valley splitting

February 6th, 2013  |  Published in All, News, Preprints

Whilst silicon is a promising material for quantum computation, the degeneracy of the conduction band minima (valleys) must be lifted with a splitting sufficient to ensure formation of well-defined and long-lived spin qubits. Here we demonstrate that valley separation can be accurately tuned via electrostatic gate control in a metal-oxide-semiconductor quantum dot, providing splittings spanning 0.3 – 0.8 meV. The splitting varies linearly with applied electric field, with a ratio in agreement with atomistic tight-binding predictions. We demonstrate single-shot spin readout and measure the spin relaxation for different valley configurations and dot occupancies, finding one-electron lifetimes exceeding 2 seconds. Spin relaxation occurs via phonon emission due to spin-orbit coupling between the valley states, a process not previously anticipated for silicon quantum dots. An analytical theory describes the magnetic field dependence of the relaxation rate, including the presence of a dramatic rate enhancement (or hot-spot) when Zeeman and valley splittings coincide.

Spin-valley lifetimes in a silicon quantum dot with tunable valley splitting

(Submitted on 5 Feb 2013)

For the first time, an experiment in small silicon quantum dots at the University of New South Wales in Australia has observed evidence of spin-valley state mixing via spin-orbit coupling, implying that roughness plays a critical role in the physics of valley states in silicon quantum dot qubits.

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