Room temperature Organic Exciton-Polariton Condensate in a Lattice

TL;DR

The work demonstrates a flexible, ambient-condition platform for room-temperature organic exciton-polaritons in a one-dimensional lattice, addressing the cryogenic limitations of traditional polariton systems. By embedding fluorescent protein gain material (mCherry) in hemispheric microcavity traps and enclosing them in high-reflectivity DBRs, the authors realize a strong-coupling system with a robust bandstructure and observable Bloch bands ($E_R$ on the order of $240\,\mathrm{meV}$). They show controlled loading of the condensate into lattice modes with distinct orbital symmetries and observe a self-localized gap-soliton state driven by the interplay of nonlinear interactions and negative effective mass, supported by an open-dissipative Gross-Pitaevskii modelling framework. This organic platform offers low cost, tunability, and operation at ambient temperature, enabling on-chip bosonic simulators and potential explorations of topological polaritons and related phenomena.

Abstract

Interacting Bosons, loaded in artificial lattices, have emerged as a modern platform to explore collective manybody phenomena, quantum phase transitions and exotic phases of matter as well as to enable advanced on chip simulators. Such experiments strongly rely on well-defined shaping the potential landscape of the Bosons, respectively Bosonic quasi-particles, and have been restricted to cryogenic, or even ultra-cold temperatures. On chip, the GaAs-based exciton-polariton platform emerged as a promising system to implement and study bosonic non-linear systems in lattices, yet demanding cryogenic temperatures. In our work, we discuss the first experiment conducted on a polaritonic lattice at ambient conditions: We utilize fluorescent proteins as an excitonic gain material, providing ultra-stable Frenkel excitons. We directly take advantage of their soft nature by mechanically shaping them in the photonic one-dimensional lattice. We demonstrate controlled loading of the condensate in distinct orbital lattice modes of different symmetries, and finally explore, as an illustrative example, the formation of a gap solitonic mode, driven by the interplay of effective interaction and negative effective mass in our lattice. The observed phenomena in our open dissipative system are comprehensively scrutinized by a nonequilibrium model of polariton condensation. We believe, that this work is establishing the organic polariton platform as a serious contender to the well-established GaAs platform for a wide range of applications relying on coherent Bosons in lattices, given its unprecedented flexibility, cost effectiveness and operation temperature.

Figures (4)

• Figure 1: Schematic images and angle-resolved measurements of our device.a - c, Artistic illustration of single trap (a), molecular configuration (b) and one-dimensional lattice (c). The hemispheric indentations are filled with the "mCherry" proteins (red). d - f, Angle-resolved photoluminescence spectrum of a single trapping site (d), as well as a molecular configuration (e) and the one-dimensional lattice (f), proving the formation of a bandgap polariton spectrum resulting from evanescent coupling between the sites. White lines show calculated single-particle energy bands in the effective periodic potential of the depth - 160 meV. The measurements are recorded at a detuning between the cavity photon and exciton energy of $\Delta=E_C-E_X=$ - 100 meV (at $k=0$ of the ground Bloch-band).
• Figure 2: Excitation power-dependent analysis of an one-dimensional lattice.a - d, Far-field photoluminescence spectra recorded at various pump powers. Excitation with a continuous wave laser (a), the white line shows calculated single-particle energy s-band in the effective periodic potential. Angled-resolved spectra for pump powers at the condensation threshold (b, P = 1.5 nJ/pulse), above the threshold (c, P = 6.0 nJ/pulse) and far past the threshold (d, P = 29.9 nJ/pulse). The condensed mode moves into the gap. e, Integrated emission intensity (black) and linewidth (red) versus excitation energy. At P = 1.5 nJ/pulse the linwidth drops to the resolution limit of the spectrometer whereas the intensity clearly features a superlinear increase. f, Excitation power-dependent blueshift of the mode.
• Figure 3: Controlled loading of the polariton condensate in the lattice. off-site versus on-site pumping and formation of corresponding gap state condensates.a, d, e, Far-field spectra below (left) and above (right) the condensation threshold, corresponding with the pump-potential alignment inserted with a sketch of the position of the pump laser spot (green) aligned with respect to the polariton potential. b, Spatial coherence measurement under on-site excitation above threshold and c, extracted coherent magnitude of the interference pattern.
• Figure 4: Self localization of a gap-solitonic mode.a, b, Energy-resolved realspace images under on-site pumping conditions little above threshold (a, P = 2.4 nJ/pulse), and far above threshold (b, P = 18.9 nJ/pulse). c, d, The intensity traces are fitted by a $sech^{2}$ and an exponential function. For the lower excitation power the $sech^{2}$-function fits to the intensity profile while for higher excitation power the exponential function fits better. In the insets, the same profiles are shown in log scale. Spatial narrowing of the extension of the condensate characterize the gap-soliton mode.