Ultrastrong-coupling phenomena beyond the Dicke model

Tuomas Jaako, Ze-Liang Xiang, Juan José Garcia-Ripoll, and Peter Rabl
Phys. Rev. A 94, 033850 – Published 27 September 2016

Abstract

We study effective light-matter interactions in a circuit QED system consisting of a single LC resonator, which is coupled symmetrically to multiple superconducting qubits. Starting from a minimal circuit model, we demonstrate that, in addition to the usual collective qubit-photon coupling, the resulting Hamiltonian contains direct qubit-qubit interactions, which have a drastic effect on the ground- and excited-state properties of such circuits in the ultrastrong-coupling regime. In contrast to the superradiant phase transition expected from the standard Dicke model, we find an opposite mechanism, which at very strong interactions completely decouples the photon mode and projects the qubits into a highly entangled ground state. These findings resolve previous controversies over the existence of superradiant phases in circuit QED, but they more generally show that the physics of two- or multiatom cavity QED settings can differ significantly from what is commonly assumed.

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  • Received 3 August 2016

DOI:https://doi.org/10.1103/PhysRevA.94.033850

©2016 American Physical Society

Physics Subject Headings (PhySH)

Atomic, Molecular & Optical

Authors & Affiliations

Tuomas Jaako1,*, Ze-Liang Xiang1, Juan José Garcia-Ripoll2, and Peter Rabl1

  • 1Vienna Center for Quantum Science and Technology, Atominstitut, TU Wien, Stadionallee 2, 1020 Vienna, Austria
  • 2Instituto de Física Fundamental, IFF-CSIC, Calle Serrano 113b, E-28006 Madrid, Spain

  • *tuomas.jaako@ati.ac.at

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Issue

Vol. 94, Iss. 3 — September 2016

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