# Bose-Einstein Condensation in a Plasmonic Lattice

## TL;DR

This paper reports the first observation of Bose-Einstein condensation of surface plasmon polaritons in a nanoparticle lattice, achieved through ultrafast thermalization at room temperature, with potential for on-chip quantum technologies.

## Contribution

It demonstrates a novel BEC of surface plasmon polaritons in a lattice, with ultrafast thermalization and a tunable crossover to lasing, advancing plasmonic quantum coherence research.

## Key findings

- Observation of BEC in plasmonic lattice modes
- Ultrafast thermalization within picoseconds
- Crossover from BEC to lasing by band structure engineering

## Abstract

Bose-Einstein condensation is a remarkable manifestation of quantum statistics and macroscopic quantum coherence. Superconductivity and superfluidity have their origin in Bose-Einstein condensation. Ultracold quantum gases have provided condensates close to the original ideas of Bose and Einstein, while condensation of polaritons and magnons have introduced novel concepts of non-equilibrium condensation. Here, we demonstrate a Bose-Einstein condensate (BEC) of surface plasmon polaritons in lattice modes of a metal nanoparticle array. Interaction of the nanoscale-confined surface plasmons with a room-temperature bath of dye molecules enables thermalization and condensation in picoseconds. The ultrafast thermalization and condensation dynamics are revealed by an experiment that exploits thermalization under propagation and the open cavity character of the system. A crossover from BEC to usual lasing is realized by tailoring the band structure. This new condensate of surface plasmon lattice excitations has promise for future technologies due to its ultrafast, room-temperature and on-chip nature.