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

Abstract

Although 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 the 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 read-out and measure the spin relaxation for different valley configurations and dot occupancies, finding one-electron lifetimes exceeding 2 s. 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. The presence of multiple minima, or valleys, in the conduction band of group IV semiconductors can be a problem for spin-based quantum computing, but can also enable alternative qubit implementations. Yang et al. demonstrate electrostatic control of the valleys’ energy splitting in a silicon quantum dot.