Compromise-Free Scaling of Qubit Speed and Coherence

TL;DR

This paper demonstrates a hole spin qubit in Ge/Si nanowires that simultaneously enhances operational speed and coherence time by leveraging a tunable Rashba spin-orbit interaction, overcoming the traditional speed-coherence trade-off.

Contribution

It introduces a novel qubit design that exploits gate-tunable spin-orbit interaction to achieve concurrent improvements in speed and coherence, breaking the conventional trade-off barrier.

Findings

Tripled Rabi frequency with quadrupled coherence time

Over an order of magnitude increase in Q-factor

Identification of a gate voltage point for optimal speed and protection

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.