  Under adequate conditions, cavity-polaritons form a macroscopic coherent
quantum state, known as Bose-Einstein condensate (BEC). Compared to
Wannier-Mott excitons in inorganic semiconductors, the localized Frenkel
excitons in organic emitter materials show weaker interaction but stronger
coupling, which recently enabled the first realization of BEC at room
temperature. However, this required ultrafast optical pumping which limits the
applications of organic BECs. Here, we demonstrate room-temperature BEC of
cavity-polaritons in simple laminated microcavities filled with the
biologically produced enhanced green fluorescent protein (eGFP). The unique
molecular structure of eGFP prevents exciton annihilation even at high
excitation densities, thus facilitating BEC under conventional nanosecond
pumping. BEC is clearly evidenced by a distinct threshold, an
interaction-induced blueshift of the condensate, long-range coherence and the
presence of a second threshold at higher excitation density which is associated
with the onset of photon lasing and results from thermalization of the exciton
reservoir.
