Real-time two-axis control of a spin qubit

TL;DR

This paper presents a real-time control protocol for a spin qubit that uses FPGA-based feedback to adaptively estimate and compensate for environmental fluctuations, significantly improving qubit stability and coherence.

Contribution

The study introduces a novel FPGA-driven feedback system for real-time Hamiltonian estimation and control of a two-electron spin qubit, enabling dynamic stabilization without magnetic field gradients.

Findings

Extended coherence of qubit rotations through feedback correction.

Real-time estimation of Overhauser field and exchange interaction.

Enhanced qubit stability and performance under fluctuating conditions.

Abstract

Optimal control of qubits requires the ability to adapt continuously to their ever-changing environment. We demonstrate a real-time control protocol for a two-electron singlet-triplet qubit with two fluctuating Hamiltonian parameters. Our approach leverages single-shot readout classification and dynamic waveform generation, allowing full Hamiltonian estimation to dynamically stabilize and optimize the qubit performance. Powered by a field-programmable gate array (FPGA), the quantum control electronics estimates the Overhauser field gradient between the two electrons in real time, enabling controlled Overhauser-driven spin rotations and thus bypassing the need for micromagnets or nuclear polarization protocols. It also estimates the exchange interaction between the two electrons and adjusts their detuning, resulting in extended coherence of Hadamard rotations when correcting for fluctuations of both qubit axes. Our study emphasizes the critical role of feedback in enhancing the performance and stability of quantum devices affected by quasistatic noise. Feedback will play an essential role in improving performance in various qubit implementations that go beyond spin qubits, helping realize the full potential of quantum devices for quantum technology applications.