MajuLab Seminar by Alberto Bramati – 27 June 2024

lberto Bramati received his PhD in physics in 1998 at the Laboratoire Kastler Brossel in Paris on the generation of squeezed states in semiconductor lasers. After a two-years post-doc in the group of Pr. Lugiato on optical solitons and quantum imaging, he joined Sorbonne University where he is full professor since 2008. His main research topics are in the framework of Quantum Optics, Quantum Information and Nano-Photonics. In the last years he focussed on the study of polariton systems, quantum fluids of light and soild states quantum emitters,  obtaining several pioneering results: among them the first demonstration of polariton superfluidity, hydrodynamic dark solitons and polarized single photon sources.

Elected OSA Fellow in 2015, he is currently senior member of the Institut Universitaire de France.

Quantum Fluids of light

Photons confined in optical cavities or propagating in paraxial geometries acquire an effective mass and behave like matter particles. Moreover, an effective photon-photon interaction can be engineered when the photons propagate in a nonlinear medium, resulting in collective fluid-like behaviors of light, such as superfluidity. The characterization of the elementary excitations in such quantum fluids of light [1] is essential to study their collective effects.

I will present a novel coherent probe spectroscopy technique to study the Bogoliubov dispersion of these excitation modes in a fluid of microcavity exciton-polaritons under resonant pumping [2]. Thanks to the unprecedented spectral and spatial resolution, we observe directly the low-energy sonic behaviour and detect the negative-energy modes, i.e. the ghost branch, of the dispersion relation. This technique provides the missing tool for the quantitative study of quantum hydrodynamics in polariton fluids.

In the second part of the talk, I will show how this technique allows to observe spontaneous symmetry breaking in a parametrically driven microcavity, revealing the appearance of a diffusive Goldstone mode; a new phenomenology stemming from the out of equilibrium nature of the system [3].

Finally, I will show how the properties of polariton quantum fluids can be used to simulate astrophysical objects like Black Holes and I will briefly discuss our progresses on the experimental investigation of the Hawking effect in a quantum fluid of polaritons.

[1] I. Carusotto and C. Ciuti, Quantum Fluids of Light, Rev. Mod. Phys. 85, 299 (2013).

[2] F. Claude, M. Jacquet, R. Usciati, I. Carusotto, E. Giacobino, A. Bramati, Q. Glorieux, Phys. Rev. Lett. 129, 103601 (2022) Title: High-Resolution Coherent Probe Spectroscopy of a Polariton Quantum Fluid

[3] M. Wouters et al. “Goldstone mode of optical parametric oscillators in planar semiconductor microcavities in the strong coupling regime”. Phys. Rev. A 76 043807 (2007)

MajuLab is an international joint research unit of the CNRS, UCA, SU, NUS and NTU in Singapore (IRL 3654), hosted by CQT and SPMS.