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

TL;DR

This paper demonstrates fast control, initialization, and measurement of an exchange-only spin qubit, with methods for state tomography and fidelity assessment applicable to complex quantum systems.

Contribution

It introduces a comprehensive approach for controlling and characterizing exchange-only spin qubits, including state tomography techniques for systems with leakage and noisy measurements.

Findings

75 qubit rotations in under 2 ns

High-fidelity single-shot readout achieved

Methods applicable to systems with leakage and noise

Abstract

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.