title: Genetic design of enhanced valley splitting towards a spin qubit in silicon.
abstract: The long spin coherence time and microelectronics compatibility of Si makes it an attractive material for realizing solid-state qubits. Unfortunately, the orbital (valley) degeneracy of the conduction band of bulk Si makes it difficult to isolate individual two-level spin-1/2 states, limiting their development. This degeneracy is lifted within Si quantum wells clad between Ge-Si alloy barrier layers, but the magnitude of the valley splittings achieved so far is small--of the order of 1 meV or less--degrading the fidelity of information stored within such a qubit. Here we combine an atomistic pseudopotential theory with a genetic search algorithm to optimize the structure of layered-Ge/Si-clad Si quantum wells to improve this splitting. We identify an optimal sequence of multiple Ge/Si barrier layers that more effectively isolates the electron ground state of a Si quantum well and increases the valley splitting by an order of magnitude, to ~9 meV.
authors.affiliation: 1] University of Colorado, Boulder, Colorado 80309, USA [2] National Renewable Energy Laboratory, Golden 80401, Colorado, USA.
authors.forename: Lijun
authors.initials: L
authors.lastname: Zhang
authors.forename: Jun-Wei
authors.initials: JW
authors.lastname: Luo
authors.forename: Andre
authors.initials: A
authors.lastname: Saraiva
authors.forename: Belita
authors.initials: B
authors.lastname: Koiller
authors.forename: Alex
authors.initials: A
authors.lastname: Zunger