Acceptor-based hole spin qubits in silicon*

Spins qubits in silicon are appealing to build quantum computers due to their small area, long coherence times, and compatibility with industrial manufacturing processes. Spin-orbit coupling is appealing to improve the scalability of such systems, enabling simple, long-distance schemes for single-qubit and multi-qubit operations, using microwave photons, phonons, or capacitive coupling [1,2]. A fundamental question is whether qubit coherence time must be sacrificed for qubits with strong spin-orbit coupling, as typically observed over the last 10 to 15 years. Here we present experimental results showing that this is emphatically not the case. We demonstrate 10 millisecond spin coherence times for holes bound to acceptor atoms in isotope purified silicon [3], where spin-orbit coupling yields quantized total angular momentum $J=3/2$, rivaling electron spin qubits, and $10^4$ to $10^5$ times longer than previous spin-orbit qubits in silicon. The key ingredient is to suppress the longitudinal electric dipole by controlling the energy separation of the $|m_J|=1/2$ and $|m_J|=3/2$ doublets, using strain. Recent theory shows that this holds not only for impurities [3] but also quantum dots [4] and for group IV materials, not just Si. These results suggest group IV hole spin qubits as an ideal platform for ultra-fast, highly coherent scalable quantum computing.

 

[1] Ruskov and Tahan, Phys. Rev. B, 88, 064308, 2013.

[2] Tosi et al, Nature Communications 8, 450, 2017.

[3] Kobayashi, Salfi et al, Nature Materials 20 38 2021.

[4] Wang, Marcellina et al, npj Quantum Information 7, 1, 2021.