The Naked Scientists

The Naked Scientists Forum

Author Topic: What is a entanglement?  (Read 3259 times)

Offline yor_on

  • Naked Science Forum GOD!
  • *******
  • Posts: 11993
  • Thanked: 4 times
  • (Ah, yes:) *a table is always good to hide under*
    • View Profile
What is a entanglement?
« on: 10/11/2011 21:25:36 »
1. Does a entanglement crave opposite spins for photons. If not, how do we define them as entangled? Their common history/ancestry?

2. If I assume that by interacting with one of the photons I impart a momentum, will that momentum also exist in its 'twin'?

2a. If I assume that there always will be needed to be a opposite effect, what happens to the momentum in the 'twin'?


 

Offline JP

  • Neilep Level Member
  • ******
  • Posts: 3366
  • Thanked: 2 times
    • View Profile
What is a entanglement?
« Reply #1 on: 10/11/2011 21:58:17 »
1. No.  Particles can be entangled in many ways, and spin is just one possible way.  They can be theoretically entangled in many properties: position, momentum, energy, angular momentum.  Spin is a very easy one to use experimentally, however.

2. Only if they're entangled in momentum, which isn't necessarily the case. 

2a.  Doesn't really apply since 2 doesn't.
 

Offline yor_on

  • Naked Science Forum GOD!
  • *******
  • Posts: 11993
  • Thanked: 4 times
  • (Ah, yes:) *a table is always good to hide under*
    • View Profile
What is a entanglement?
« Reply #2 on: 10/11/2011 22:40:26 »
If I use a beam splitter, won't their momentum be the same? How can I define a different momentum to them?
=
letting them wander differently in a medium :) No, that would be an interaction that measured the entanglement, wouldn't it?
« Last Edit: 10/11/2011 22:43:31 by yor_on »
 

Offline yor_on

  • Naked Science Forum GOD!
  • *******
  • Posts: 11993
  • Thanked: 4 times
  • (Ah, yes:) *a table is always good to hide under*
    • View Profile
What is a entanglement?
« Reply #3 on: 10/11/2011 22:50:20 »
Hmm, maybe I'm missing something here? I defined it as when measuring one side of the entanglement I imparted this momentum, which I believe to be correct in all interactions? And if I get you right JP, you say that this is only the case if they are entangled in their momentum?

What does that mean?
 

Offline yor_on

  • Naked Science Forum GOD!
  • *******
  • Posts: 11993
  • Thanked: 4 times
  • (Ah, yes:) *a table is always good to hide under*
    • View Profile
What is a entanglement?
« Reply #4 on: 10/11/2011 23:09:50 »
If I choose to measure the momentum, then that momentum at the other side (B) should be a result of both the entanglement itself, plus the added momentum of my initial interaction at (A), setting the entanglements 'state', right? Even if HUP defines a uncertainty to the momentum in each individual entanglement, even when 'identical', the added momentum should still be there in each case, shouldn't it?

:) ah well. Entanglements are tricky.
« Last Edit: 10/11/2011 23:22:20 by yor_on »
 

Offline JP

  • Neilep Level Member
  • ******
  • Posts: 3366
  • Thanked: 2 times
    • View Profile
What is a entanglement?
« Reply #5 on: 11/11/2011 00:17:18 »
Think of it as a pair of coins.  I entangle them in heads and tails.  If we flip our coins and record the outcomes, we can tell they're entangled if we later compare our results and they match.

The entanglement doesn't care if we're in the same room or on the other side of the planet from each other.  It doesn't care if I'm standing still and you're flying by in a rocket ship.  The correlation is only in heads/tails, not in the momentum one of us has or where we are in space.   
 

Offline yor_on

  • Naked Science Forum GOD!
  • *******
  • Posts: 11993
  • Thanked: 4 times
  • (Ah, yes:) *a table is always good to hide under*
    • View Profile
What is a entanglement?
« Reply #6 on: 11/11/2011 09:45:43 »
I see that you want to define it as a expression of statistics JP :) But what I'm wondering about is the way I expect any interaction should impart a momentum. I also said that I expect that to be true in all interactions. If that assumption is wrong, are there any experiments, not theory, proving that we have interactions without that momentum interacting?
 

Offline yor_on

  • Naked Science Forum GOD!
  • *******
  • Posts: 11993
  • Thanked: 4 times
  • (Ah, yes:) *a table is always good to hide under*
    • View Profile
What is a entanglement?
« Reply #7 on: 11/11/2011 10:09:57 »
Macroscopically I can't think of any? If we go down in scale we can speak about waves, quenching and reinforcing, would quenching describe such a situation, or is that totally unrelated? What does the momentum of a wave function means? Its phase?
 

Offline imatfaal

  • Neilep Level Member
  • ******
  • Posts: 2787
  • rouge moderator
    • View Profile
What is a entanglement?
« Reply #8 on: 11/11/2011 11:37:39 »
And measuring and imparting momentum is difficult to tell apart in these circumstances - once you are gaining information or imparting information about one entangled particle (and thus about the other) you have broken the entanglement.  No matter how many pop-science programmes say that you can separate two entangled particles of a quantum pair and use them to communicate - this cannot happen. 

No matter how far apart when I look at my electron it will have the same properties as the entangled other of the pair that Yoron has taken to Proxima Centuri - but if I impart new information - spin, ang mom etc then the entanglment is broken and nothing spectacular will have to Yorons.  In fact Yoron's particle will remain in the same state as mine was - and this is where is it useful; if I measure (and in the process necessarily disrupt) my electrons properties I still know that Yoron's unmeasured engtangled electron has these same properties (not the new ones, the old ones)
 

Offline yor_on

  • Naked Science Forum GOD!
  • *******
  • Posts: 11993
  • Thanked: 4 times
  • (Ah, yes:) *a table is always good to hide under*
    • View Profile
What is a entanglement?
« Reply #9 on: 11/11/2011 13:19:52 »
Hmm, that's not how I understand a entanglement Imatfaal? The superposition or 'pristine' undisturbed wave function only exist before the entanglements measurement. As soon as someone make a measurement 'both sides'Ęshould fall out, even before the second party measures his. It would be interesting if you was right though, a sort of 'delayed' effect of a superposition, coming in two stages.
 

Offline yor_on

  • Naked Science Forum GOD!
  • *******
  • Posts: 11993
  • Thanked: 4 times
  • (Ah, yes:) *a table is always good to hide under*
    • View Profile
What is a entanglement?
« Reply #10 on: 13/11/2011 15:11:56 »
It seems to be a matter of definition which way you look at it though. I like to expect a causality chain myself, from that view, excluding the idea of 'virtual particles', also expecting all to have a direction in time a entanglement/wave function can only be operated on once. That will set its 'state', once for all with no 'sides' of it existing, as I see it.

Although the definition of nothing having to have happened at 'B' before you measure it, and then also able to see it as if 'B' sets 'A:s' wave function too, even though you measured 'A' first exist, it makes no sense from my definition as I don't see 'time' so 'fragmented'. But you are certainly right in that both definitions exist.
 

The Naked Scientists Forum

What is a entanglement?
« Reply #10 on: 13/11/2011 15:11:56 »

 

SMF 2.0.10 | SMF © 2015, Simple Machines
SMFAds for Free Forums
 
Login
Login with username, password and session length