Phys Rev Lett. 2014 May 09;112(18):180405. doi: 10.1103/PhysRevLett.112.180405. Epub 2014 May 08.

Hybrid quantum magnetism in circuit QED: from spin-photon waves to many-body spectroscopy.

Physical review letters

Andreas Kurcz, Alejandro Bermudez, Juan José García-Ripoll

PMID: 24856680 DOI: 10.1103/PhysRevLett.112.180405

Abstract

We introduce a model of quantum magnetism induced by the nonperturbative exchange of microwave photons between distant superconducting qubits. By interconnecting qubits and cavities, we obtain a spin-boson lattice model that exhibits a quantum phase transition where both qubits and cavities spontaneously polarize. We present a many-body ansatz that captures this phenomenon all the way, from a the perturbative dispersive regime where photons can be traced out, to the nonperturbative ultrastrong coupling regime where photons must be treated on the same footing as qubits. Our ansatz also reproduces the low-energy excitations, which are described by hybridized spin-photon quasiparticles, and can be probed spectroscopically from transmission experiments in circuit QED, as shown by simulating a possible experiment by matrix-product-state methods.

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• Journal Article