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Towards spin dynamics in SiGe quantum dots

A single electron spin confined in a quantum dot is one of the most promising realisations of a quantum bit (qubit). While research efforts have mainly focused on electrons, EU scientists proposed to study holes.
Towards spin dynamics in SiGe quantum dots
The EU-funded project SPIDERMAN (Electronic transport and spin dynamics through SiGe self-assembled quantum dots) explored the potential of silicon-germanium (SiGe) nanostructures for the realisation of spin qubits. In Si and Ge, electrons' spins can have long relaxation and coherence times due to small hyperfine interaction. It has been shown that spin coherence times for electrons in Silicon can approach 1 second. However, much less is known about confined holes which have an even lower hyperfine interaction.

The SPIDERMAN team aimed to realise SiGe quantum dot devices out of nanostructures. SiGe nanostructures were self-assembled through lattice-mismatched hetero-epitaxial growth, where Ge was deposited on a Si substrate.

Within the course of the project, the scientists were successful in modulating the hole g-factor in SiGe nanostructures – namely, the response of the spin of holes confined in SiGe to an external magnetic field. The giant modulations were achieved when an electric field was applied along the growth direction. Such an electrically tunable hole g-factor in quantum dots is highly desired for applications in quantum computing as well as in spintronics.

In addition, the scientists used the Luttinger Hamiltonian that describes the valence band structure to find an explanation for this unusual behaviour. They attributed the strong modulation of the hole g-factor to a relative displacement of the heavy-hole and the light-hole wave functions when an electric field was applied.

SPIDERMAN results suggest that hole spins in self-organised SiGe nanostructures, can be electrically manipulated with frequencies in the order of 100 MHz. The experimental work carried out stresses the hitherto largely overlooked potential of holes as spin qubits and were the first important steps towards the realization of a hole spin qubit in SiGe self-assembled nanostructures.

Related information

Keywords

Spin dynamics, quantum dots, electron spin, SPIDERMAN, silicon-germanium, hole g-factor
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