Photons and free quantum particles

[hokhani]

TL;DR

Are photons localised?

Consider a light source, like lamb, that radiates photons in vacuum. Can we detect a particular photon, moving in a specific direction, always at one point or the photon is localised and moves from one point to another? In other words, I would like to know that like free quantum particles, photons also have the probability of presence everywhere?

 

[PeterDonis]

Can we detect a particular photon, moving in a specific direction, always at one point or the photon is localised and moves from one point to another?

These are two different questions.

"Moving in a specific direction" is a question about momentum. Photons do have a well-defined momentum operator, so yes.

"Localised" is a question about position. Photons do not have a well-defined position operator, so no.

 

[pines-demon]

Consider a light source, like lamb,

I know this is a typo but lambs do emit photons (even in vacuum).