Nonadiabatic quantum control of valley states in silicon

Abstract

Non-adiabatic quantum effects, often experimentally observed in semiconductors nano-devices such as single-electron pumps operating at high frequencies, can result in undesirable and uncontrollable behaviour. However, when combined with the valley degree of freedom inherent to silicon, these unfavourable effects may be leveraged for quantum information processing schemes. By using an explicit time evolution of the Schrodinger equation, we study numerically non-adiabatic transitions between the two lowest valley states of an electron in a quantum dot formed in a SiGe/Si heterostructure. The presence of a single atomic layer step at the top SiGe/Si interface opens an anti-crossing in the electronic spectrum as the centre of the quantum dot is varied. We show that an electric field applied perpendicularly to the interface allows tuning of the anti-crossing energy gap. As a result, by moving the electron through this anti-crossing, and by electrically varying the energy gap, it is possible to electrically control the probabilities of the two lowest valley states.