Novel Spin Qubits

As qubits are mapped on a speed-coherence plane, a pattern emerges: achieving greater coherence often comes at the cost of operational speed, a widely discussed but rarely quantified trade-off that may limit qubit performance. Systems using strong spin-orbit interaction (SOI) for rapid control via electric dipole spin resonance (EDSR) may be especially susceptible to charge noise coupling through the driving field, making hole spins particularly vulnerable, underlining the need to more deeply understand the driving mechanisms behind spin-orbit qubits.

Our proof-of-concept work demonstrates a hole spin qubit in a Ge/Si core/shell nanowire able of achieving a coherence sweet spot at maximal qubit speed, via the control of a local electric field. Our approach triples the qubit speed and quadruples the Hahn-echo coherence time, without compromising one another [1], thereby boosting the Q-factor by almost an order of magnitude.

In addition, we apply a two-tone pulse spectroscopy to resolve and extract the exchange interaction J between two hot hole spin qubits, which appears to be on a similar order of magnitude as the Rabi frequency. This further allows us to drive conditional two-qubit rotations at 1.5 K [2], thereby laying the foundation for realising entangling two-qubit logic gates beyond the millikelvin regime.

These breakthroughs open up new possibilities for designing scalable, high-performance quantum processors based on hole spins, without the drawbacks that have long impacted their development.