Optimal conveyor-mode shuttling of electron spin qubits by employing a 2D map of the local valley splitting

Long-range coherent qubit coupling is a promising functional block for a scalable architecture of a spin-qubit based quantum computer. In a conveyor-mode shuttle, the spin-qubit is adiabatically transported while confined in a propagating sinusoidal potential in a gate-defined quantum channel [1]. Its key feature is the all-electrical operation by only few easily tunable input terminals. During shuttling spin dephasing and relaxation is predicted to occur due to stochastic valley excitations at spots of tiny local valley splitting and at spin-valley relaxation hotspots, respectively [1].

We explore electron-spin shuttling in conveyor-mode on a state-of-art ²⁸Si/SiGe heterostructure [2]. Prior to the analysis of spin qubit decoherence during shuttling, we map the valley splitting [3,4]. While shuttling, we find partial valley excitations resulting in quick spin dephasing in regions of tiny valley splitting. Crossing a spin-valley hotspot at which the Zeeman equals valley splitting energy, quick spin relaxation depending on shuttle velocity occurs. Avoiding such regions [5], we spin-coherently shuttle across a distance of 280 nm 100 times forth and back, which sums up to a total shuttle distance of 50 µm.

[1] Langrock ea., PRX Quantum 4 (2023).

[2] Wuetz ea., Nat. Commun. 14, 1385 (2023).

[3] Volmer ea., npj Quantum Inf. 10, 61 (2024).

[4] Struck eal., Nat. Commun. 15, 1325 (2024).

[5] Losert ea., arXiv 2405.01832.