Tuning the coherent interaction of an electron qubit and a nuclear magnon

TL;DR

This paper demonstrates precise tuning of the interaction between an electron spin qubit and a nuclear spin ensemble in a GaAs quantum dot, enabling control over collective nuclear excitations and qubit coherence for quantum information applications.

Contribution

It introduces a method for in situ, high-precision tuning of electron-nuclear interactions in a GaAs quantum dot using nuclear sideband spectroscopy and feedback control.

Findings

Achieved isotopically selective nuclear spectroscopy revealing the Knight field.

Controlled the activation rate of nuclear magnons.

Enhanced electron qubit coherence time through interaction tuning.

Abstract

A central spin qubit interacting coherently with an ensemble of proximal spins can be used to engineer entangled collective states or a multi-qubit register. Making full use of this many-body platform requires tuning the interaction between the central spin and its spin register. GaAs quantum dots offer a model realization of the central spin system where an electron qubit interacts with multiple ensembles of $\sim 10^{4}$ nuclear spins. In this work, we demonstrate tuning of the interaction between the electron qubit and the nuclear many-body system in a GaAs quantum dot. The homogeneity of the GaAs system allows us to perform high-precision and isotopically selective nuclear sideband spectroscopy, which reveals the single-nucleus electronic Knight field. Together with time-resolved spectroscopy of the nuclear field, this fully characterizes the electron-nuclear interaction for a priori control. An algorithmic feedback sequence selects the nuclear polarization precisely, which adjusts the electron-nuclear exchange interaction in situ via the electronic g-factor anisotropy. This allows us to tune directly the activation rate of a collective nuclear excitation (magnon) and the coherence time of the electron qubit. Our method is applicable to similar central-spin systems and enables the programmable tuning of coherent interactions in the many-body regime.