Genetic design of enhanced valley splitting towards a spin qubit in silicon
نویسندگان
چکیده
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.
منابع مشابه
Enhanced Valley Splitting in Silicon Nanowires and Point Contacts
Splitting between equivalent valleys larger than the spin splitting is reported in a laterally confined electron system in thin Si films grown on SiGe substrate. We demonstrate that the enhanced splitting can be explained within a simple model of the conduction band structure in silicon. Our results are in good agreement with recent first-principle calculation data. Due to the weak spin-orbit c...
متن کاملTheory of valley-orbit coupling in a Si/SiGe quantum dot
Electron states are studied for quantum dots in a strained Si quantum well, taking into account both valley and orbital physics. Realistic geometries are considered, including circular and elliptical dot shapes, parallel and perpendicular magnetic fields, and most importantly for valley coupling the small local tilt of the quantum-well interface away from the crystallographic axes. In absence o...
متن کاملSpin Lifetime Dependence on Valley Splitting in Thin Silicon Films
Electron spin attracts much attention as an alternative to the electron charge degree of freedom for low-power re-programmable logic and non-volatile memory applications. In contrast to charge, spin is not a conserved quantity, and having sufficiently long spin lifetime is critical for applications. We investigate spin relaxation in (001) SOI structures depending on the splitting between the eq...
متن کاملValley splitting in Si quantum dots embedded in SiGe
We examine energy spectra of Si quantum dots embedded in Si0.75Ge0.25 buffers using atomistic numerical calculations for dimensions relevant to qubit implementations. The valley degeneracy of the lowest orbital state is lifted and valley splitting fluctuates with monolayer frequency as a function of the dot thickness. For dot thicknesses 6 nm, valley splitting is found to be 150 eV. Using the u...
متن کامل