Why would FTL not be possible even in a noiseless place?

[San K]

I am illustrating this via both questions and an experiment both of which are conceptually are dealing with the same idea.

http://en.wikipedia.org/wiki/Coincidence_counting_(physics )

Question:


1 a) if there were zero noise, and only single photon was sent, do we need a co-incidence counter?

1 b) is it practically possible to have zero noise?

2. if not, could we do FTL of information?


let's look at the below setup and tell me what i am missing (or wrong assumptions) in the logic below:

Alice, Bob and Charlie

Alice sends entangled photons to Bob and Charlie and a Delayed choice quantum eraser is setup between Bob and Charlie (and Alice).

Alice and Bob are sitting close by while Charlie is on a distant planet

Signal photon is going towards Bob and Idler towards Charlie

its decided that:

if Alice wants to communicate 1 to Charlie she creates a no-which-way pattern (interference)

if Alice wants to communicate 0 to Charlie she creates a which-way pattern (no-interference)

so now to communicate to Charlie, Alice and Bob work with the signal photon.

they want to send the information digit 1 to say Charlie FTL, so they pass the photon through the polarizer setup such that which-way info is erased.

Now when Charlie looks at his photon's behavior he sees that the photon is detected on the interference pattern bands...i.e. the photon lands up on one of the intereference bands...on his detector D

Note: before this was done, a million photons were sent earlier and thus the bands were formed...and marked on the detector.

Now after that...the above experiment was done where only 1 single photon was sent.

Since there is no noise (i.e. no photons from outside the experiement striking the detector) Charlie (alice and bob) don't need a co-incidence counter.

All charlie does is...watch where the photon struck. Did the photon lie on the interference band/fringes or between them? and he would know (with higher than 50% probability) what was done to the signal photon by alice and bob.

 

[Nugatory]

This approach fails for the same reason that so many other attempts to use entanglement for FTL communication fail: Alice and Bob cannot control the behavior of their particle without interacting with it and ending the entanglement. Thus Charlie will see the same pattern no matter what Alice and Bob do, and the effects of the entanglement will only be apparent when they compare notes after the fact.

(It is possible for Alice and Bob to things that affect the pattern that Charles observes - trivially they could block on of the slits - but in this case the message is being by carried by the photons themselves so there is no FTL involved).