Martina Morassi

Inside a tiny mirrored cavity, smaller than the thickness of a hair, light is trapped and bounces off the walls many times. If you place a material that can absorb and emit light inside, the light particles (photons) start to 'dress' in excitations of the material — this is how polariton modes are born.

Two musicians in separate rooms play the same note. The sound must be so identical that a listener can't tell who is playing. In the quantum world, these musicians are single-photon sources — particles of light that must be indistinguishable from one another.