# Strong photon coupling to the quadrupole moment of an electron in solid state

## TL;DR

This paper demonstrates strong coupling between a quadrupole moment of an electron in a triple quantum dot and microwave photons, showing potential for more coherent quantum information processing.

## Contribution

The authors experimentally realize a quadrupole qubit in a triple quantum dot and achieve strong photon coupling with improved coherence properties.

## Key findings

- Strong quadrupole qubit-photon coupling demonstrated
- Enhanced qubit coherence when dipole coupling is minimized
- Potential for more noise-resilient quantum devices

## Abstract

The implementation of circuit quantum electrodynamics allows coupling distant qubits by microwave photons hosted in on-chip superconducting resonators. Typically, the qubit-photon interaction is realized by coupling the photons to the electric dipole moment of the qubit. A recent proposal suggests storing the quantum information in the electric quadrupole moment of an electron in a triple quantum dot. The qubit is expected to have improved coherence since it is insensitive to dipolar noise produced by distant voltage fluctuators. Here we experimentally realize a quadrupole qubit in a linear array of three quantum dots in a GaAs/AlGaAs heterostructure. A high impedance microwave resonator coupled to the middle dot interacts with the qubit quadrupole moment. We demonstrate strong quadrupole qubit--photon coupling and observe improved coherence properties when operating the qubit in the parameter space where the dipole coupling vanishes.