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

Jonne V. Koski, Andreas J. Landig, Maximilian Russ, José C. Abadillo-Uriel, Pasquale Scarlino, Benedikt Kratochwil, Christian Reichl, Werner Wegscheider, Guido Burkard, Mark Friesen, Susan N. Coppersmith, Andreas Wallraff, Klaus Ensslin, Thomas Ihn

Published 2019-05-02Version 1

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.