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Circuit QED: Coupling Superconducting Qubits via a Cavity Bus on a Chip

Dr. Johannes Majer
TU Wien


Circuit quantum electrodynamics is a system that allows us to carry out new experiments in quantum optics using a superconducting integrated circuit on a chip. In circuit QED, microwave photons are guided and confined by superconducting transmission lines and cavities, and can then be coherently coupled to a transmon qubit. This system leads to a much stronger coupling of “light” and “matter” than is possible with traditional atomic systems. Making use of this strong coupling, it is possible to couple two qubits via the cavity[1]. I will show how one can use the cavity as a coupling bus which provides non-local and non-nearest-neighbor coupling. The interaction is mediated by the exchange of virtual rather than real photons, avoiding cavity-induced loss. The same cavity is also used to perform multiplexed control and read-out of the two qubits. The coupling is effectively switchable which allows for time-domain transfer of the quantum states between the qubits.



J. Majer, J. M. Chow, J. M. Gambetta, Jens Koch, B. R. Johnson, J. A. Schreier, L. Frunzio, D. I. Schuster, A. A. Houck, A. Wallraff, A. Blais, M. H. Devoret, S. M. Girvin and R. J. Schoelkopf.
Coupling superconducting qubits via a cavity bus
Nature 449 443 (2007)