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 $S=3$. More particularly, we report the formation of a hybridized spin quintet state and show triplet-quintet and quintet-septet spin blockade. This enables studies of the quintet relaxation dynamics from which we find $T_1 \sim 4 ~\mu s$. 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 open for the possibility of using Si CMOS quantum dots as a tuneable platform for studying high-spin systems.
Highlights
High-spin states have been shown to play a key role in a variety of important physical phenomena
Our study provides a comprehensive understanding of spin-blockade physics in systems with a dense energy spectrum and allows for the possibility of investigating the dynamics of high-spin systems using programmable complementary metal-oxide-semiconductor (CMOS) technology
In order to study the spin physics and energy spectrum of the multielectron double quantum dots (DQDs) defined in this device, and, in particular, of the interdot charge transition (ICT) shown in Fig. 1(b), we perform a dispersive magnetospectroscopy study by measuring the line trace intersecting the ICT at VGmw 1⁄4 0.440 V while increasing the magnetic field B, which is applied in plane with the device and at an 83° angle to the nanowire
Summary
High-spin states have been shown to play a key role in a variety of important physical phenomena. Given that silicon possesses an additional valley degree of freedom [28], the energy spectrum in silicon quantum dots can be rather complex, and accurately identifying when singlet-triplet blockade occurs is of importance for achieving reliable and scalable readout of spin qubits in silicon. To better understand the magnetic dependence of the dispersive response, we develop a quantum capacitance model that enables reconstruction of the energy spectrum of the coupled DQD, including the spin-dependent tunnel coupling and the energy splitting between different spin manifolds. Our study provides a comprehensive understanding of spin-blockade physics in systems with a dense energy spectrum and allows for the possibility of investigating the dynamics of high-spin systems using programmable CMOS technology
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