Room-temperature superfluidity in a polariton condensate (1609.03153v1)

Abstract: Superfluidity---the suppression of scattering in a quantum fluid at velocities below a critical value---is one of the most striking manifestations of the collective behaviour typical of Bose-Einstein condensates. This phenomenon, akin to superconductivity in metals, has until now only been observed at prohibitively low cryogenic temperatures. For atoms, this limit is imposed by the small thermal de Broglie wavelength, which is inversely related to the particle mass. Even in the case of ultralight quasiparticles such as exciton-polaritons, superfluidity has only been demonstrated at liquid helium temperatures. In this case, the limit is not imposed by the mass, but instead by the small exciton binding energy of Wannier-Mott excitons, which places the upper temperature limit. Here we demonstrate a transition from normal to superfluid flow in an organic microcavity supporting stable Frenkel exciton-polaritons at room temperature. This result paves the way not only to table-top studies of quantum hydrodynamics, but also to room-temperature polariton devices that can be robustly protected from scattering.

• The paper presents the first observation of room-temperature superfluidity in a polariton condensate using an organic microcavity design.
• It employs a pulsed laser and microscopy to reveal suppressed scattering and density modulation around defects.
• Numerical modeling with the Gross-Pitaevskii equation confirms a critical density of ~10^7 polaritons/µm², opening new avenues for photonic applications.

Room-Temperature Superfluidity in a Polariton Condensate

The paper of superfluidity in quantum fluids, traditionally limited to cryogenic temperatures, has seen remarkable advancement with the exploration of polariton condensates. This paper presents an investigation into room-temperature superfluidity within an organic microcavity supporting Frenkel exciton-polaritons, a significant leap over conventional environments constrained by low cryogenic temperatures.

Context and Motivation

Historically, superfluidity has been a key element in understanding quantum fluid dynamics, deeply entwined with Bose-Einstein condensation (BEC). Observing this phenomenon typically required temperatures close to absolute zero, as seen with conventional BEC experiments like those involving ultracold atom systems. Here, the challenge lies in overcoming the temperature limits posed by excitonic and quasiparticle systems.

Methodology

The authors have utilized an optical microcavity configuration, integrating TDAF organic molecules sandwiched between dielectric mirrors. This design forms stable Frenkel exciton-polaritons with significant Rabi energy allowing observation at room temperature. Exciton-polaritons are chosen due to their advantageous properties such as large exciton binding energies, which facilitate the transition to a superfluid state at elevated temperatures.

Experimental Conditions and Observations

• Microscopy Setup: The excitation and detection were accomplished using microscope objectives positioned at the substrate and cavity sides respectively, with a pulsed laser resonant with the lower polariton branch to facilitate the creation of polariton wavepackets.
• Defect Interaction: The experiment demonstrated a transition from a normal to a superfluid flow in polaritons as they encountered defects. The suppression of scattering and modulation of density in front of and around defects were pivotal indicators of superfluidity.
• Density and Velocity Effects: A notable density of approximately $10^7 \, \text{pol}/\upmu\text{m}^2$ was identified as critical for achieving superfluidity, with the behavior also intricately linked to group velocity adjustments.

Numerical Modeling

Theoretical modeling was conducted using the time-dependent Gross-Pitaevskii equation tailored to the specific polariton mass and interaction dynamics. The consistency of model predictions with experimental data underscores the robustness of the methods employed.

Significance and Future Potential

The implications of room-temperature superfluidity in polariton condensates are multifaceted:

• Table-top Quantum Hydrodynamics: The findings advocate for accessible experimental setups for studying quantum fluid dynamics, bypassing the requirement for extreme cooling infrastructure.
• Photonic Circuitry: Potential applications extend to photonic devices, where scattering and reflection losses could be minimized or eliminated using polariton superfluidity, enhancing device efficiency and performance.
• Interdisciplinary Advances: These results have the potential to further unify concepts across optics, condensed matter physics, and quantum mechanics, potentially influencing next-generation technology development.

Conclusion

This work establishes a pivotal step in achieving room-temperature quantum fluidity, offering a new arena for studying and leveraging quantum mechanical phenomena. Further research could focus on exploring the scalability of this system, the coherence properties over extended conditions, and leveraging these findings in practical photonic applications, expanding the horizons of quantum technology.