• Colloque CPTGA
• Personne à contacter : Julia Meyer ()
• Lieu : Amphithéâtre, maison des Magistères

Résumé : We will discuss interesting properties of open quantum graphs and microwave networks [1]. We will demonstrate that there exist graphs which do not obey the Weyl’s law N(R) = LR/π + O(1), where O(1) is a function which for R going to infinity is bounded by a constant. The Weyl’s law directly links the counting function N(R) of the number of resonances with the square root of energy k, 0(k), and the total length L of the internal edges of a graph. Graphs which do not obey the Weyl’s law are called non-Weyl graphs. We show that for standard coupling conditions the transition from a Weyl graph to a non-Weyl graph occurs if we introduce a balanced vertex. A vertex of a graph is called balanced if the numbers of infinite leads and internal edges meeting at a vertex are the same. The experimental results demonstrating the existence of non-Weyl networks are in excellent agreement with the theoretical predictions [2].

Acknowledgements

References

• [1]. O. Hul, S. Bauch, P. Pakoński, N. Savytskyy, K. Życzkowski, and L. Sirko, Phys. Rev. E 69, 056205 (2004).
• [2]. M. Ławniczak, J. Lipovsky, and L. Sirko, Phys. Rev. Lett. 122, 140503 (2019).

• Séminaire nano-électronique quantique
• Personne à contacter : Robert Whitney ()
• Lieu : Salle Rémy Lemaire K223, Institut Néel

Résumé :

In cavity quantum electrodynamics (QED), the interaction between an atomic transition and the cavity field is measured by the vacuum Rabi frequency omega_0. The regime with omega_0 comparable to the two-level transition frequency is called the ultrastrong coupling regime. In such a regime, and for a large number of atoms coupled to the same cavity mode, a superradiant quantum phase transitions (SQPT) has been predicted, e.g. within the Dicke model.

In this theoretical seminar, I will briefly describe the SQPT at equilibrium, discuss the experimental context, and present our recent proposal where a 2DEG with Rashba spin-orbit coupling placed inside an optical cavity can exhibit the SQPT.

Ref: P. Nataf, T. Champel, G. Blatter, and D. M. Basko, Rashba cavity qed: a route towards the superradiant quantum phase transition, arXiv:1907.02938 (2019)

• Séminaire théorie
• Personne à contacter : Serge Florens ()
• Lieu : Amphithéâtre, maison des Magistères

Résumé : After briefly summarizing my long-term interest in quantum physics of low-dimensional spinless fermions that attract each other, I will present our recent study of a quantum many-body lattice system of one-dimensional fermions interacting with a dynamical Z2 gauge field. The gauge field mediates long-range attraction between fermions resulting in their confinement into bosonic dimers. At strong coupling we developed an exactly solvable effective theory of such dimers with emergent constraints. I will show that even at a generic coupling and fermion density, the model can be rewritten as a local spin 1/2 chain and forms a Luttinger liquid. In a finite chain we observed the doubling of the period of Friedel oscillations which paves the way towards experimental detection of confinement in this system. Finally, I will also discuss the possibility of a Mott phase at the commensurate filling 2/3, connection to quantum scars and our plans to extend this study to two spatial dimensions in pursuit of exotic p-wave superfluidity.

Liens :[Sergej Moroz]