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Accueil > Séminaires > Archive des séminaires d’Utinam > 2018

Simone Felicetti

Ultrastrong coupling regime of two-photon interactions

jeudi 26 avril 2018, 10h30

Salle de conférences de l’observatoire

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Laboratoire Matériaux et Phénomènes Quantiques, Université Paris Diderot

Résumé :

Two-photon processes have so far been considered only as effective models to describe quantum optical systems subjected to strong classical drivings. In this case, two-photon interactions (TPI) arise from second- or higher-order effects, and so they are limited to extremely small coupling strengths. However, a ariety of novel physical phenomena emerges in the strong or ultrastrong coupling regime, where such coupling values become comparable to dissipation rates or even to the system bare frequencies, respectively. For instance, in the ultrastrong coupling regime of TPI a spectral collapse [1] can take place, i.e. the system discrete spectrum can collapse in a continuous band.

In this contribution, I will present different schemes to implement TPI using current quantum technologies and recent theoretical analysis on the physics of such models. First, I will present a quantum-simulation protocol [2], [3] where a trapped-ion system is used to implement ultrastrong TPI between a chain of qubits and a single bosonic mode. We analyzed the many-body limit of this model, revealing a rich interplay between the spectral collapse and the superradiant phase transition [4]. Then, we designed a superconducting circuit scheme to implement genuine TPI in a solid-state device [5]. An open quantum system analysis shows that fundamental quantum optical phenomena are qualitatively modified with respect to standard dipolar interactions. We find that realistic parameters allow to reach the spectral collapse, where extreme nonlinearities are expected to emerge at the few-photon level.