Accurate spin and valley state identification in silicon double quantum dots*

To read the state of silicon spin qubits, the mechanism that has provided highest fidelity is spin-to-charge conversion via Pauli spin blockade [1]. However, given the valley degree of freedom in silicon quantum dots, which can lead to complex energy spectra, accurate identification of the spin states involved in Pauli spin blockade is a key requirement for reliable readout and operation of silicon spin qubits.

Here, we expand the standard description of Pauli spin blockade in a double quantum dots (DQD) to include multiparticle states with large total spin angular momentum S. Using gate-based dispersive readout and magnetospectroscopy, we show successive steps of spin blockade and spin-blockade lifting involving spin states up to S=3 as well as the formation of a novel spin-quintet state [2]. Furthermore, we demonstrate the use of this technique for discerning whether the valleys involved in DQD interdot transitions are of equal or different quantum number.

[1] Harvey-Collard et al, Phys. Rev. X 8, 021046 (2018)
[2] Lundberg et al, Phys. Rev. X 10, 041010 (2020)