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


The fundamental concept of light–matter interaction is routinely realized by coupling the quantized electric field in a cavity to the dipole moment of a real or an artificial atom. A recent proposal1,2, motivated by the prospect of overcoming the decohering effects of distant charge fluctuations, suggests that introduction of and coupling to an electric quadrupole moment of a single electron can be achieved by confining it in a triple quantum dot. Here, we show an experimental realization of this concept by connecting a superconducting microwave resonator to the middle of the three dots, such that the dipole coupling becomes negligible. We demonstrate strong coupling to the electron quadrupole moment and determine that the coherence of our system is limited by short-range charge noise. Our experiment enables the construction and detection of a complex electronic state of a single electron in a solid-state environment that does not exist as such for a free electron.

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Fig. 1: Schematics of the qubit wavefunctions and the device.
Fig. 2: Qubit charge configuration and resonator amplitude response.
Fig. 3: Qubit–photon interaction.
Fig. 4: Determination of qubit energy and linewidth.

Data availability

The data represented in Figs. 24 are provided with the manuscript as source data. All other data that support the plots within this paper and other findings of this study are available from the corresponding author upon reasonable request.


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We thank C. K. Andersen and M. Collodo for useful discussions and D. van Woerkom for his contribution to the sample fabrication. This work was supported by the Swiss National Science Foundation through the National Center of Competence in Research (NCCR) Quantum Science and Technology. S.N.C. and M.F. acknowledge support by the Vannevar Bush Faculty Fellowship programme sponsored by the Basic Research Office of the Assistant Secretary of Defense for Research and Engineering and funded by the Office of Naval Research through grant no. N00014-15-1-0029. M.R. and G.B. acknowledge funding from the Army Research Office (ARO) through grant no. W911NF-15-1-0149 and the DFG through grant SFB 767. M.F. and J.C.A.-U. acknowledge support by ARO (W911NF-17-1-0274). The views and conclusions contained herein are those of the authors and should not be interpreted as necessarily representing the official policies or endorsements, either expressed or implied, of the ARO or the US Government. The US Government is authorized to reproduce and distribute reprints for Governmental purposes, notwithstanding any copyright notation thereon.

Author information




J.V.K., A.J.L. and P.S. fabricated the device. J.V.K. and A.J.L. performed the measurements with input from B.K. J.V.K. analysed the measurement data. J.V.K., J.C.A.-U. and M.R. wrote the manuscript with input from all authors. C.R. grew the heterostructure under the supervision of W.W. M.R. derived the input–output model under the supervision of G.B. J.C.A.-U. and M.R. developed the charge noise and magnetic field models under the supervision of G.B., M.F. and S.N.C. A.W., T.I. and K.E. supervised the experiment.

Corresponding author

Correspondence to J. V. Koski.

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Supplementary information

Supplementary Information

Supplementary Figs. 1–3 and Discussion.

Source data

Source Data Fig. 2

Measurement and simulation data of Fig. 2

Source Data Fig. 3

Measurement and simulation data of Fig. 3

Source Data Fig. 4

Measurement and simulation data of Fig. 4

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Koski, J.V., Landig, A.J., Russ, M. et al. Strong photon coupling to the quadrupole moment of an electron in a solid-state qubit. Nat. Phys. 16, 642–646 (2020).

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