Collective excitations of a bound-in-the-continuum condensate

Area of Science:

• Quantum physics
• Condensed matter physics
• Optics

Background:

• Characterizing bosonic quantum fluids relies on understanding elementary excitation spectra.
• Observing these spectra is challenging due to low occupation of non-condensate states.
• Low-threshold Bose-Einstein condensation was recently achieved in a symmetry-protected bound state.

Purpose of the Study:

• To explore the intrinsic collective properties of long-living polariton condensates.
• To unveil the peculiar features of the Bogoliubov spectrum of excitations in this system.
• To investigate the impact of a dark bound-in-the-continuum state on excitation observability.

Main Methods:

• Utilizing a system with Bose-Einstein condensation coupled to semiconductor excitons.
• Leveraging the dark nature of the bound-in-the-continuum state for enhanced observation.
• Analyzing the Bogoliubov spectrum of collective excitations.

Main Results:

• Collective excitations above the condensate are observable in enhanced detail.
• Identified energy-flat dispersion parts with two parallel photoluminescence stripes.
• Observed linearization at non-zero momenta and strongly anisotropic sound velocity.

Conclusions:

• The dark nature of the bound state facilitates detailed study of polariton condensate excitations.
• The observed spectral features offer new insights into quantum fluid dynamics.
• This work opens avenues for exploring novel quantum phenomena in polariton systems.