Spin Qubit Leapfrogging: Dynamics of shuttling electrons ontop of another

In recent years spin shuttling has distinguished itself as a promising candidate for achieving

high fidelity medium range interactions between spin qubits and presents a powerful tool

for enabling scalable semiconductor spin quantum computing architectures in the future.

A dominant source of errors encountered during spin shuttling in silicon are regions of low valley splitting, which can lead to leakage, dephasing and also rapid spin relaxation.

Modelling the process of a shuttled spin qubit encountering a stationary quantum dot, we

investigate the dynamics of the (1,1)-(0,2) charge transition in a silicon double quantum dot

with non-vanishing inter-valley coupling. This enables us to describe the process of the mobile

electron leapfrogging over the stationary one i.e. transitioning from a (1,1,0)- to a (0,1,1)-charge

state, occupying a (0,2,0)-state inbetween. Here the triplets will occupy a valley excited state to

circumvent Pauli-Spin-Blockade leading to a singlet-triplet splitting approximately equal to the valley splitting

in the stationary dot. Consequently this protocol will implement an entangling gate, which can

be tuned by waiting in this configuration. For the gate to be noise-resistant and controllable the valley splitting at the location of the middle dot needs to be very low.

Therefore this opens up the possibility to make practical use and isolate low-valley-splitting hotspots on a wafer, which would otherwise act as error sources.