Abstract
Spins in gate-defined silicon quantum dots are promising candidates for implementing large-scale quantum computing. To read the spin state of these qubits, the mechanism that has provided the highest fidelity is spin-to-charge conversion via singlet-triplet spin blockade, which can be detected in situ using gate-based dispersive sensing. In systems with a complex energy spectrum, like silicon quantum dots, accurately identifying when singlet-triplet blockade occurs is hence of major importance for scalable qubit readout. In this work, we present a description of spin-blockade physics in a tunnel-coupled silicon double quantum dot defined in the corners of a split-gate transistor. Using gate-based magnetospectroscopy, we report successive steps of spin blockade and spin-blockade lifting involving spin states with total spin angular momentum up to . More particularly, we report the formation of a hybridized spin-quintet state and show triplet-quintet and quintet-septet spin blockade, enabling studies of the quintet relaxation dynamics from which we find . Finally, we develop a quantum capacitance model that can be applied generally to reconstruct the energy spectrum of a double quantum dot, including the spin-dependent tunnel couplings and the energy splitting between different spin manifolds. Our results allow for the possibility of using Si complementary metal-oxide-semiconductor quantum dots as a tunable platform for studying high-spin systems.
- Received 3 December 2019
- Revised 11 April 2020
- Accepted 5 August 2020
DOI:https://doi.org/10.1103/PhysRevX.10.041010
Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.
Published by the American Physical Society
Physics Subject Headings (PhySH)
Popular Summary
Electronic states with high amounts of spin are central to the understanding of novel physical phenomena such as energy collection in organic photovoltaics and unconventional high-spin superconductivity. Identifying the arrangement of spins is also paramount for the accurate readout of quantum information stored in silicon quantum dots. These atomlike solid-state systems, where individual electrons can be collected on demand, are particularly promising for large-scale quantum computing. Here, we present a method that enables spin order identification and, as a result, the discovery of high-spin states in silicon quantum dots.
Our work achieves this milestone by developing an energy spectroscopy tool based on dispersive radio-frequency readout and by expanding the standard description of Pauli spin blockade—the typical method for reading out spin qubits—to include high-spin states. Our methodology allows us to discover a novel spin system not previously identified in silicon quantum dots: a spin quintet, a multiparticle state consisting of four unpaired electrons. We use this finding as an opportunity to investigate the spin quintet’s dynamical properties, thereby assessing its suitability for quantum computing applications.
Overall, our methods and results provide a pathway for reconstructing energy spectra of complex spin systems and open the possibility of using industrially fabricated quantum dots as a tunable test bed for studying the interactions and dynamics of high-spin systems such as the spin quintet.
