AQP Seminar: Stimulated thermalization and long-range spatial coherence of Bose-Einstein condensates in plasmonic lattices

Abstract: 

We study Bose–Einstein condensation of surface plasmon polaritons in strongly coupled lattice modes of a nanoparticle array covered with fluorescent molecules at room temperature. The plasmonic condensate is a manifestation of macroscopic quantum coherence in unprecedented, sub-picosecond, timescales. We study the dynamics in an experiment that utilizes the open cavity character of the system. Spatially resolved spectra and momentum space measurements reveal three distinct regimes as a function of excitation pump fluence: lasing, (incomplete) thermalization, and Bose-Einstein condensation [1]. By varying the lattice size, we show that the thermalization occurs through a stimulated process. Experiments with Michelson interferometer in a retroreflector configuration show that the condensation is accompanied by extended spatial coherence in two dimensions. Above the condensation threshold, the first-order spatial correlation function is nearly constant over array sizes up to half a millimeter [2]. We find that both spatial and temporal coherence display non-exponential decay; the results suggest power-law or stretched exponential behaviour with different exponents for spatial and temporal correlation decays. 

References

[1] Väkeväinen, A. I., Moilanen, A. J., Nečada, M., Hakala, T. K., Daskalakis, K. S., and Törmä, P., Sub-picosecond Thermalization Dynamics in Condensation of Strongly Coupled Lattice Plasmons, Nature Communications 11, 3139 (2020) 

[2] Moilanen, A. J., Daskalakis, K. S., Taskinen, J., and Törmä, P., Spatial and Temporal Coherence of Strongly Coupled Plasmonic Bose-Einstein Condensates, preprint in arXiv:2103.10397v1 [cond-mat.quant-gas] (2021) https://arxiv.org/abs/2103.10397