Self-Consistent Measurement and State Tomography of an Exchange-Only Spin Qubit

Understand

We report initialization, complete electrical control, and single-shot readout of an exchange-only spin qubit.

• Full control via the exchange interaction is fast, yielding a demonstrated 75 qubit rotations in under 2 ns.
• Measurement and state tomography are performed using a maximum-likelihood estimator method, allowing decoherence, leakage out of the qubit state space, and measurement fidelity to be quantified.
• The methods developed here are generally applicable to systems with state leakage, noisy measurements, and non-orthogonal control axes.