Shanghai Institute Of Optics And Precision Machinery Makes Progress in Synergistic Exciton Polarization Exciton Bose Einstein Condensation

Recently, the team of Researcher Dong Hongxing and Researcher Zhang Long from Infrared Optical Materials Research Center, Department of Advanced Laser and Optoelectronic Functional Materials, Shanghai Institute of Optics Precision Machinery, Chinese Academy of Sciences (SIPM), in collaboration with East China Normal University (ECNU), has resolved the kinetic process and its physical mechanism of the phase transition from superfluorescence to synergetically exciton-polarized exciton coalescence in it based on the chalcogenide quantum dots thin-film system, with the related research results being published as The related research results were published in the journal "Observation of Transition from Superfluorescence to Polariton Condensation in CsPbBr3 Quantum Dots Film". -Science & Applications.
A large number of dipoles are spontaneously synchronized by a vacuum field to form a macroscopic dipole moment and produce a brief and intense burst of light, the so-called superfluorescence. Hyperfluorescence is an ideal platform to study the many-body correlation mechanism in exciton systems and to develop bright quantum light sources and ultrafast optical technologies. Meanwhile, the characteristics of cooperative excitons with higher vibronic intensity are conducive to the study of nonlinear properties of cooperative excitons, and it is easier to realize the coalescence of cooperative exciton polarized excitons, which can help to expand the applications in the fields of quantum logic gates, topological state excitations, and so on. At present, there is still a gap in the study of the regulation of the coupling strength between light and cooperative matter states and the phase transition mechanism from hyperfluorescence to coexciton polarized exciton condensation. Realizing the tuning of the coupling strength between light and cooperative matter states based on the quantum dot system and resolving the ultrafast phase transition regulated by the cavity optical field are crucial for the further development and application of quantum devices.
In view of this, the researchers proposed to introduce an external cavity to tune the coupling strength of light and cooperative excitons, based on the distributed Bragg reflector half-cavity on the structure of chalcogenide quantum dots thin film proved the strong coupling phenomenon between the cooperative excitons and the Bragg mode, the Rabi cleavage of 21.6 meV. In addition, in the course of the study, the phenomenon of coalescence of the cooperative excitons polarization exciton was also observed. The involved correlated excitons exhibit significant coupling enhancement, a phenomenon mainly due to the random phase synchronization caused by the synergistic effect induced excitons, which results in the formation of macroscopic dipole moments with consistent polarization directions. The realization of the new quasiparticle Bose Einstein condensation provides new possibilities for the development of ultra-narrow tunable lasers. In addition, the two-optical-matter property of the synergistic exciton polarized exciton condensation promotes the potential applications of synergistic exciton polarized exciton condensation in quantum simulations, unconventional coherent light sources, and all-optical polarization logic devices.
This work is supported by the National Natural Science Foundation of China, Shanghai Young Top Talent Program, Shanghai Leading Talent Program and other programs.

Fig. 1 (a) Schematic structure of a quantum dot film on DBR substrate; (b) hyperfluorescence spectra of a quantum dot film on silicon substrate and reflectance spectra of DBR substrate; (c) Angle-resolved photoluminescence spectra of a quantum dot superlattice thin film on DBR; (d) Calculation of the density of states of the polarized exciton versus angle and wavelength; (e) second-order derivative plot of Fig. (c); and (f) Angle-resolved reflectance spectra of DBR.