Spin-Blockade Spectroscopy of Si/SiGe Quantum Dots

TL;DR

This paper introduces a fast, reliable method for measuring singlet-triplet energy splitting in Si/SiGe quantum dots, revealing that spin-blockade may be limited by orbital excitation energies rather than valley splitting.

Contribution

The authors develop and demonstrate an in situ technique for measuring singlet-triplet splitting in Si/SiGe quantum dots, applicable across various energy regimes.

Findings

Measured splitting varies smoothly with gate biases.

Spin-blockade can be limited by orbital excitation energy.

Technique is useful for device tuning and characterization.

Abstract

We implement a technique for measuring the singlet-triplet energy splitting responsible for spin-to-charge conversion in semiconductor quantum dots. This method, which requires fast, single-shot charge measurement, reliably extracts an energy in the limits of both large and small splittings. We perform this technique on an undoped, accumulation-mode Si/SiGe triple-quantum dot and find that the measured splitting varies smoothly as a function of confinement gate biases. Not only does this demonstration prove the value of having an $in~situ$ excited-state measurement technique as part of a standard tune-up procedure, it also suggests that in typical Si/SiGe quantum dot devices, spin-blockade can be limited by lateral orbital excitation energy rather than valley splitting.