Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Splitting photons are entangled?

  1. Sep 5, 2011 #1
    I'm sorry if this is a silly question and please forgive me but, if you split photons into two by any medium or matter can it entangle photons? Do the photons have to go through a beta barium borate crystal or any other crystals? Are there any alternatives to split photons? Please provide good info and please no negative comments. Thank you.
  2. jcsd
  3. Sep 5, 2011 #2


    User Avatar

    What do you mean by 'splitting photons'? Photons are never 'split'. Downconversion, occuring at BBO crystal is not a 'split': the photon just excites the crystal, which then emits pair of photons.
  4. Sep 5, 2011 #3
    what i mean is that when a photon goes in the crystal, it splits right? what im asking is that can i do parametric downconversion on any other medium or matter and can it split with that option? i dont have anything in mind, im just curious.

    here is the source where i got the information about splitting photons:

    Last edited by a moderator: Apr 26, 2017
  5. Sep 5, 2011 #4


    User Avatar

    Photons do not 'split'. What happens in BBO is that original photon is absorbed, and two brandly new photons are emitted.
    BBO crystal is not the only means (but most common for practical purposes of experiments in optical range) to create entangled photons.

    For example: if the positronium annihilates into two gamma photons - they are also perfectly entangled.
  6. Sep 5, 2011 #5
    so, im guessing that there is no other option to entangle photons. last question, do we have to use crystals to do parametric downconverison or is there a alternative, if so why?
  7. Sep 5, 2011 #6


    User Avatar
    Science Advisor

    Strictly speaking they are not absorbed and reemitted. As this is a parametric process there is virtual absorption at best and no real absorption. A more solid description is given when examining the polarization arising inside the non-linear medium which is basically the eigenstate of the em field inside that medium. As the polarization contains non-linear response the possibility for sum- or difference frequency generation opens up and one can get down-conversion.

    Ehm, as xts already said there are other possibilities. You could also use other parametric processes like the output from an OPO. Also there are schemes that rely on parametric scattering to generate entangled particles, especially in polariton systems.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook