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 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 such as silicon quantum dots, accurately identifying when singlet-triplet blockade occurs is therefore critical 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 S = 3. Furthermore, we report the formation of a hybridized spin quintet state and show triplet-quintet and quintet-septet spin blockade. This enables investigation of the quintet relaxation dynamics from which we find a relaxation time of T1 ~ 4 µs. Finally, we develop a quantum capacitance model that is applied generally to reconstruct the energy spectrum of the double quantum dot including the spin-dependent tunnel coupling and the energy splitting between different spin manifolds. Our results open the possibility of using silicon complementary metal-oxide-semiconductor (CMOS) quantum dots as a tuneable platform for studying the interactions and dynamics of high-spin systems.

References

1) https://arxiv.org/abs/1910.10118

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