Universal quantum control of two-electron spin quantum bits using dynamic nuclear polarization

TL;DR

This paper demonstrates universal quantum control of two-electron spin qubits with nanosecond gate times by employing magnetic field gradients generated through dynamic nuclear polarization, enabling arbitrary qubit rotations.

Contribution

It introduces a method to achieve full quantum control of two-electron spin qubits using magnetic field gradients from dynamic nuclear polarization, enabling fast, arbitrary rotations.

Findings

Achieved nanosecond-scale universal control of two-electron spin qubits.

Generated stable magnetic field gradients via dynamic nuclear polarization.

Demonstrated quantum state tomography confirming control.

Abstract

One fundamental requirement for quantum computation is to perform universal manipulations of quantum bits at rates much faster than the qubit's rate of decoherence. Recently, fast gate operations have been demonstrated in logical spin qubits composed of two electron spins where the rapid exchange of the two electrons permits electrically controllable rotations around one axis of the qubit. However, universal control of the qubit requires arbitrary rotations around at least two axes. Here we show that by subjecting each electron spin to a magnetic field of different magnitude we achieve full quantum control of the two-electron logical spin qubit with nanosecond operation times. Using a single device, a magnetic field gradient of several hundred milliTesla is generated and sustained using dynamic nuclear polarization of the underlying Ga and As nuclei. Universal control of the two-electron qubit is then demonstrated using quantum state tomography. The presented technique provides the basis for single and potentially multiple qubit operations with gate times that approach the threshold required for quantum error correction.