High-fidelity single-spin shuttling and conveyor two-qubit gate in Si/SiGe

Maxim De Smet

Efficient quantum error correction in spin qubit systems relies on strong qubit connectivity within the architecture [1]. In semiconductor heterostructures, exchange-based two-qubit interactions are typically limited to nearest-neighbor couplings due to their intrinsic short range. To overcome this limitation, recent advancements have focused on utilizing superconducting resonators [2] and on physically displacing spin qubits.

We create a quantum link by shuttling a single electron spin across a linear array of six tunnel-coupled quantum dots in an isotopically enriched ²⁸Si/SiGe heterostructure. An electron can be shuttled through the array in bucket brigade mode by sequentially pulsing both the electrochemical potential of each quantum dot and the interdot tunnel barriers [3,4,5]. Alternatively, sinusoidal voltage signals can be applied to all the channel gates to create a conveyor potential [6,7]. We benchmark both bucket-brigade and conveyor-mode shuttling while transporting the electron back and forth from the second to the fifth quantum dot. Conveyor-mode shuttling reaches a transport fidelity of 99.6% for an effective shuttle distance of 10 μm in only 184 ns.

Furthermore, we can leverage the shuttling of electron spins for qubit operations. In this talk, I will present a high-fidelity controlled-Z (CZ) gate, activated by bringing two electron spins close together by conveyor-mode shuttling. By shuttling each electron to the linear array's midpoint, a saturation of the exchange coupling can be observed. The CZ fidelity, assessed through randomized benchmarking, reaches 99.4%. We next utilize the conveyor-style two-qubit gate to accomplish quantum state teleportation. Specifically, the quantum state of the spin localized in dot 6 is conditionally teleported to the spin located in dot 2.

[1] Xu et al., Nature Physics 20, 1084–1090 (2024)

[2] Dijkema et al., Nature Physics (2024)

[3] T. Fujita et al., npj Quantum Information 3, 22 (2017)

[4] J. Yoneda et al., Nature Communications 12, 4114 (2021)

[5] A. Noiri et al., Nature Communications 13, 5740 (2022)

[6] I. Seidler et al., npj Quantum Information 8, 100 (2022)

[7] Struck et al., Nature Communications 15, 1325 (2024)