# Photon emission.

1. Aug 6, 2011

### cragar

If a photon is emitted from the nucleus of an atom, and the atom is at rest is the photon and the atom entangled? If their spin angular momentum was zero before the emission. And is it possible to have an atom emit a photon from its nucleus and one of its electrons at the same time, and would all 3 of these particles be entangled. Or does entanglement only work between 2 particles.

2. Aug 6, 2011

### DiracRules

I'm not technically prepared on this questions, but as I read a lot of divulgence books I just answer the last question.:tongue:

It has been created a state of three entangled particles (photons) as well as four. The main advances in the field were carried by the GHZ (after Greenberg-Horne-Zeilinger) team, which managed to obtain the first three-particle entangled state.

Anton Zeilinger also managed to teleport a photon :D

http://en.wikipedia.org/wiki/Greenberger-Horne-Zeilinger_state" [Broken]

Last edited by a moderator: May 5, 2017
3. Aug 6, 2011

### Bill_K

You know, long before the word "entanglement" came onto the popular scene, we used to call it coherence. And yes, all the products resulting from a single reaction are coherent until they are observed or interfered with. A more typical example of a nuclear reaction would be beta decay, in which an electron and neutrino are emitted. And they will be coherent with each other and with the daughter nucleus, meaning that their spins and energies are correlated, but in principle not determined until a measurement takes place, even if they travel to alpha centauri first. The trick comes not in producing such a situation, but in detecting it.

4. Aug 6, 2011

### ibysaiyan

The poster above me has already answered to most of the doubts highlighted in the OP but technically isn't it impossible to have an atom at rest or is my thinking wrong? I mean for an atom to be at rest would imply zero energy or an integer below absolute zero :s

5. Aug 6, 2011

### DiracRules

If you consider Heisenberg principle, to have an atom at completely rest you must have it delocalized everywhere in the space
$\sigma_x\cdot\sigma_p\geq\frac{\hbar}{2}$

So, even if theoretically you could achieve such condition, it's obviously impossible:tongue2:...

6. Aug 7, 2011

### cragar

Now that I think about it you don't need an atom to be at rest to have entangled particles. Like what Bill K said, the trick is detecting the event.