Compromise-free scaling of qubit speed and coherence
Miguel J. Carballido, Simon Svab, Rafael S. Eggli, Taras Patlatiuk, Pierre Chevalier Kwon, Jonas Schuff, R. Kaiser, Leon C. Camenzind, Ang Li, Natalia Ares, Erik P. A. M. Bakkers, Stefano Bosco, J. Carlos Egues, Daniel Loss, Dominik M. Zumbühl
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. Across qubit platforms, improving coherence often compromises operational speed. Here, the authors overcome this trade-off by electrically controlling a hole spin qubit in a Ge/Si core/shell nanowire, achieving triple manipulation speeds while quadrupling coherence times.