Dominik Zumbühl

Quantum computers bring great potential to execute complex tasks exponentially faster than any classical computer. Qubits based on semiconductor spins in Si and Ge are small (nm length scale), promise excellent coherence with fast switching times, and can even be operated at elevated temperatures (above 4 K) where cooling powers are large, thus allowing integration of the classical control electronics. All of these advantages propel Si/Ge spins as a leading qubit platform.

In this talk, I will present recent progress on hole spins in Ge/Si nanowires. We can gate-voltage tune the Rabi frequency and driven coherence by about a factor of 7, and the g-factor by 50%. We can thus tune from a fast manipulation to an idle mode, demonstrating a spin–orbit switch. Further, we show ultrashort spin-flipping times down to ~1 ns, and an exceptionally strong and tunable spin-orbit coupling strength reaching down to $L_{so} \sim 4\; \text{nm}$. These qubits were also operated at 1.5 K, and have great potential for very strong spin-photon coupling.

Silicon fin field effect transistors (finFETs) are the race horse of classical transistor scaling, integrating more than 50 billion transistors on 1 cm2. We show that Si FinFETs can host hole spin qubits operating above 4 K, achieving fast all electrical control and single-qubit gate fidelities of 99% at the fault-tolerance threshold, and a Rabi oscillation quality factor greater than 87. We identify two Rabi EDSR driving mechanisms, and demonstrate a fast cROT two-qubit gate with highly gate-tunable exchange interaction. These finFETs feature industry compatibility and quality, yet are fabricated in a flexible and agile way, helping to accelerate further development.