Dresden 2014 – scientific programme

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TT: Fachverband Tiefe Temperaturen

TT 6: Transport: Quantum Coherence and Quantum Information Systems - Theory I

TT 6.4: Talk

Monday, March 31, 2014, 11:45–12:00, HSZ 204

Hybrid quantum magnetism in the strong and ultrastrong coupling regime — •Andreas Kurcz, Alejandro Bermudez, and Juan Jose Garcia-Ripoll — Instituto de Fisica Fundamental (IFF-CSIC), Calle Serrano 113bis, Madrid E-28006, Spain

We study a quantum setup that consist of superconducting qubit mediated resonators, where quantum magnetism arises non-perturbatively and can be understood both analytically and numerically (A. Kurcz et. al., arXiv:1310.8173). The setup exhibits a set of interspersed spin-boson lattice models [1,2] and reveals a phase transition of the Ising type [3], where both qubits and cavities spontaneously polarise and where the cavity-qubit detuning acts as the equivalent of a magnetic field. We develop a many-body correlated mean field theory that accurately predicts the nature of the ground state and that captures this phenomenon all the way, from a perturbative dispersive regime where photons can be traced out, to the non-perturbative 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 hybridised spin-photon quasiparticles, and can be probed spectroscopically from transmission experiments in circuit-QED, as shown by Matrix-Product-State methods. Our model offers an ideal playground in order to simulate the existing many-body machinery from spin-photon waves to many body-spectroscopy.
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