Spin filling and orbital structure of the first six holes in a silicon metal-oxide-semiconductor quantum dot

TL;DR

This paper demonstrates a silicon quantum dot capable of trapping and analyzing the first six holes, revealing strong hole-hole interactions and orbital structures consistent with Fock-Darwin spectrum, paving the way for hole spin qubits.

Contribution

It reports the first silicon quantum dot operated down to the last hole, mapping spin and orbital states, and highlighting strong hole-hole interactions relevant for quantum computing.

Findings

Mapping of spin states and orbital structure of six holes

Observation of strong hole-hole interactions reducing singlet-triplet splitting

Confirmation of Fock-Darwin spectrum in hole states

Abstract

The spin states of electrons confined in semiconductor quantum dots form a promising platform for quantum computation. Recent studies of silicon CMOS qubits have shown coherent manipulation of electron spin states with extremely high fidelity. However, manipulation of single electron spins requires large oscillatory magnetic fields to be generated on-chip, making it difficult to address individual qubits when scaling up to multi-qubit devices. The spin-orbit interaction allows spin states to be controlled with electric fields, which act locally and are easier to generate. While the spin-orbit interaction is weak for electrons in silicon, valence band holes have an inherently strong spin-orbit interaction. However, creating silicon quantum dots in which a single hole can be localised, in an architecture that is suitable for scale-up to a large number of qubits, is a challenge. Here we report a silicon quantum dot, with an integrated charge sensor, that can be operated down to the last hole. We map the spin states and orbital structure of the first six holes, and show they follow the Fock-Darwin spectrum. We also find that hole-hole interactions are extremely strong, reducing the two-hole singlet-triplet splitting by 90% compared to the single particle level spacing of 3.5 meV. These results provide a route to single hole spin quantum bits in a planar silicon CMOS architecture.