Why does the double-slit experiment with a laser work properly in an atmosphere? Likewise, I've seen news reports of entangled photons transmitted in a fiber or in open-air used to generate a shared secret. So, both superposition and entanglement works. But, the fact that the speed of the light is slower shows that the photon is interacting with the air (or fiber) molecules. (I understand that the photon mixes with quasi-particles called phonons and the resulting mixture, actually a polariton, travels with a speed slower than c. So, why doesn't the air cause rapid decoherance? You don't need to consider every air atom to perceive the entanglement. Instead, you can seemingly ignore the air (or glass).