Using all-optical methods, scientists from Skoltech and the University of Southampton, U.K., have created an artificial lattice called Lieb lattice. All nodes in the lattice hold polaritons- quasiparticles that are half-light and half-matter excitations in semiconductors.
Thi laser-generated polariton lattice allowed scientists to demonstrate breakthrough results significant for condensed matter physics. It can be used to design next-generation devices like optical computers reliant on dispersion management and guiding light.
Under the right conditions, polaritons form coherent many-body states of matter like Bose-Einstein condensates. This gives access to exotic dissipative nonlinear dynamics.
Hence, scientists decided to determine how these condensates behave in artificial optical lattices. To do so, they used a programmable spatial light modulator to shape a laser beam into a lattice inside the cavity. The generated polaritons both increased in number and became more energetic where the laser field was most intense.
The polaritons started forming condensates at high enough laser power. In this case, the condensates resided on the potential maxima of the lattice. In this so-called ballistic regime, high-energy polariton waves escaping the condensates are scattered and diffracted across the lattice.
As the lattice constant decrease, the condensate undergoes a phase transition from the ballistic regime to the opposite case of deeply trapped condensates now residing in the potential minima of the lattice.
The system can’t decide whether the polariton waves should be delocalized or localized at intermediate lattice constants. As a result, the condensates fractured across multiple energies.
Scientists further demonstrate that the lattice could produce completely dispersionless crystal bands, also known as flatbands. Within the flatlands, the particle mass becomes effectively infinite. For this, an optical Lieb lattice has been designed that posses flatbands.
Professor Pavlos Lagoudakis from the Hybrid Photonics Lab said, “Our lab has developed great expertise in optical lattices of polariton condensates, and with this work, we have taken one more step forward. These results will greatly interest a broad scientific community spanning nonlinear optics, condensed matter physics, cold atoms, light-matter physics, and polaritonics. This is the first demonstration of nontrivial phases of matter and flatband engineering in optically generated polariton lattices. Previously, flatband states in polariton systems had only been shown in lithographically written structures.”
Experimental physicist Dr. Sergey Alyatkin from Skoltech, and his colleague, theoretical physicist Dr. Helgi Sigurdsson from the University of Southampton, added: “Our work is a very nice demonstration of the advancements in optical control and richness in the field of polaritonics. The more we study microcavity polaritons in lattices, the more interesting effects we observe. Our latest results have opened a route to new physics of nonstationary lattice mixtures of matter-wave quasiparticles, and we are not confining ourselves to a specific type of investigated lattice.”
- Alyatkin, S., Sigurdsson, H., Askitopoulos, A. et al. Quantum fluids of light in all-optical scatterer lattices. Nat Commun 12, 5571 (2021). DOI: 10.1038/s41467-021-25845-4