Impact of g-factors and valleys on spin qubits in a silicon double quantum dot

TL;DR

This paper investigates the effects of g-factors and valley states on silicon spin qubits in a double quantum dot, revealing inter-valley spin-orbit coupling and a novel two-qubit gate mechanism.

Contribution

It introduces a method to analyze valley and g-factor effects on silicon spin qubits and demonstrates a new two-qubit gate approach based on triplet state transitions.

Findings

Inter-valley coupling strength of 43 MHz extracted from resonance data.

Observation of a narrow resonance indicating triplet state transitions.

Simulation shows weak exchange coupling and g-factor differences influence qubit behavior.

Abstract

We define single electron spin qubits in a silicon MOS double quantum dot system. By mapping the qubit resonance frequency as a function of gate-induced electric field, the spectrum reveals an anticrossing that is consistent with an inter-valley spin-orbit coupling. We fit the data from which we extract an inter-valley coupling strength of 43 MHz. In addition, we observe a narrow resonance near the primary qubit resonance when we operate the device in the (1,1) charge configuration. The experimental data is consistent with a simulation involving two weakly exchanged-coupled spins with a g-factor difference of 1 MHz, of the same order as the Rabi frequency. We conclude that the narrow resonance is the result of driven transitions between the T- and T+ triplet states, using an ESR signal of frequency located halfway between the resonance frequencies of the two individual spins. The findings presented here offer an alternative method of implementing two-qubit gates, of relevance to the operation of larger scale spin qubit systems.