Supporting Data For: "Compromise-Free Scaling of Qubit Speed and Coherence" (V1)

Supporting Data For: "Compromise-Free Scaling of Qubit Speed and Coherence" (V1) Miguel J. Carballido; Simon Svab; Taras Patlatiuk; Pierre Chevalier Kwon; Jonas Schuff; Rahel M. Kaiser; Leon C. Camenzind; Ang Li; Natalia Ares; Erik P.A.M. Bakkers; Stefano Bosco; J. Carlos Egues; Daniel Loss; Dominik M. Zumbühl Nature Communications (2025), DOI: 10.1038/s41467-025-62614-z Abstract Across leading qubit platforms, a common trade-off persists: increasing coherence comes at the cost of operational speed, reflecting the notion that protecting a qubit from its noisy surroundings also limits control over it. This speed-coherence dilemma limits qubit performance across various technologies. Here, we demonstrate a hole spin qubit in a Ge/Si core/shell nanowire that triples its Rabi frequency while simultaneously quadrupling its Hahn-echo coherence time, boosting the Q-factor by over an order of magnitude. This is enabled by the direct Rashba spin–orbit interaction, emerging from heavy-hole-light-hole mixing through strong confinement in two dimensions. Tuning a gate voltage, causes this interaction to peak, providing maximum drive speed and a point where the qubit is optimally protected from charge noise, allowing speed and coherence to scale together. Our proof-of-concept shows that careful dot design can overcome a long-standing limitation, offering a new approach towards building high-performance, fault-tolerant qubits.