Strong optical coupling through superfluid Brillouin lasing. (arXiv:1907.06811v1 [physics.optics])

Brillouin scattering has applications ranging from signal processing, sensing
and microscopy, to quantum information and fundamental science. Most of these
applications rely on the electrostrictive interaction between light and
phonons. Here we show that in liquids optically-induced surface deformations
can provide an alternative and far stronger interaction. This allows the
demonstration of ultralow threshold Brillouin lasing and strong phonon-mediated
optical coupling for the first time. This form of strong coupling is a key
capability for Brillouin-reconfigurable optical switches and circuits, for
photonic quantum interfaces, and to generate synthetic electromagnetic fields.
While applicable to liquids quite generally, our demonstration uses superfluid
helium. Configured as a Brillouin gyroscope this provides the prospect of
measuring superfluid circulation with unprecedented precision, and to explore
the rich physics of quantum fluid dynamics, from quantized vorticity to quantum

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