Nonadiabatic quantum control of valley states in silicon

Nonadiabatic quantum effects, often experimentally observed in semiconductor nanodevices such as single-electron pumps operating at high frequencies, can result in undesirable and uncontrollable behavior. 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 Schr\"odinger equation, we study numerically nonadiabatic 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 anticrossing in the electronic spectrum as the center of the quantum dot is varied. We show that an electric field applied perpendicularly to the interface allows tuning of the anticrossing energy gap. As a result, by moving the electron through this anticrossing, and by electrically varying the energy gap, it is possible to electrically control the probabilities of the two lowest valley states.