Light is remarkably good at keeping its polarization state intact for long distances through single mode fiber. At least historically, the main issues with doing quantum computation with light is that’s it’s hard to store light and hard to get one photon to interact with another one in a controlled manner.

(Polarization of a photon is a two-state quantum system, otherwise known as a qubit.)

Does that mean that an individual and unique photon travels the full distance from transmitter to receiver without interacting with anything?

That seems... really difficult. I'd always assumed fiber operates by continually absorbing and reemitting photons at low loss. Maybe I've fundamentally misunderstood optics.