Periodic Reporting for period 1 - ToPol (Topological Polaritonics)
Période du rapport: 2018-04-01 au 2020-03-31
This is highly relevant both at the fundamental and technological levels. At the more technological level, this could allow engineering new photonic active devices (e.g. switches, diodes, sources...) that are immune to the presence of local defects and environmental fulctuations. At the more fundamental point of view, it will pave the way to the exploration of new physical objects that are inherently nonlinear, like topological solitons or vortices. The implementation of such novel objects is crucial to better understand topological phases of matter in the presence of inter-particle interactions.
The objective of this action is precisely to study this question using exciton-polaritons confined in arrays of semiconductor microresonators. Thanks to their excitonic part, these hybrid light-matter quasiparticles exhibit strong Kerr-like nonlinearities. More specifically the objectives of this project are divided in three parts: 1- implementing topological phases of matter that break time-reversal symmetry in polaritonic arrays, 2- implementing nonlinear effects in simpler polaritonic lattices that do not break time-reversal symmetry, and 3- combined both to explore nonlinear topological physics in systems that break time-reversal.
Since the beginning of the project, the work realized can be classified in the following classes:
1- Demonstrating the onset of a lasing action in a benzene-like polaritonic molecule. This has allowed generating a coherent emission from a state that carries a well-defined topological charge. Furthermore, by using a circularly-polarized laser pump, it was possible to optically break time-reversal symmetry in a well-defined manner and control the chirality of the emission field, see image 1 attached. This is in line with the first objectvie described above, and has led to the following publication: Nat. Photonics 13, 283–288 (2019).
2- Using the device fabricated in the previous point, we were able to explore the nonlinear regime by working at high driving power. Thanks to gain saturation, we were able to observe a bistable regime between two modes carrying a distinct topological charge. This was the first observation of such a nonlinear effect with chiral light, and it is in line with the second objective described above. It has led to the following publication: Opt. Letters 44, 18, 4531-4534 (2019)
3- Recently, I have collaborated with a PhD student to observe nonlinear effects in topological arrays of higher dimensionality. Namely, we have demonstrated the onset of symmetry-protected solitons in a 1D topological lattice. This is also an important result in relation with the second objective. A manuscript is right now finalized, and should be submitted shortly to a high-impact journal.
4- In order to push the exploration of this physics in 2-dimension lattices, I have realized an important work where we have measured topological invariants in a honeycomb lattice that emulates the physics graphene, see image 2 attached. This is very relevant, as a similar lattice will be used to demonstrate (under a magnetic field) 2-dimensional topological lattices that break time-reversal symmetry. A manuscript has been updated on arXiv (2002.09528) and is currently under revision in a high-impact journal.