Directional Goldstone waves in polariton condensates close to equilibrium

Area of Science:

• Condensed matter physics
• Quantum optics
• Semiconductor physics

Background:

• Exciton-polaritons in semiconductor microcavities form quantum fluids of light.
• These quasi-particles exhibit superfluid properties analogous to Bose-Einstein condensates.

Purpose of the Study:

• To investigate the excitation spectrum of a thermalized polariton condensate.
• To study the transition from free-particle dispersion to superfluid Goldstone modes.
• To measure the critical sound speed in polariton superfluids.

Main Methods:

• Utilized microscopic oceanographic techniques to probe the polariton condensate.
• Analyzed the excitation spectrum as a function of fluid density.
• Investigated the impact of asymmetric pumping on collective excitations.

Main Results:

• Demonstrated the transition from parabolic to linear dispersion with increasing fluid density.
• Observed a sound-like Goldstone mode characteristic of superfluids.
• Showed that asymmetric pumping creates directional collective excitations.
• Measured the critical sound speed for polariton superfluids near equilibrium.

Conclusions:

• Polariton condensates exhibit superfluid behavior with a distinct Goldstone mode.
• Fluid density and pumping asymmetry significantly influence collective excitations.
• The study provides insights into the fundamental properties of quantum fluids of light.