Quantum Eraser & 50% information eraser

[StevieTNZ]

Hey there,

I was pointed to the article attached, where I am meant to find an answer as to why in the proposed quantum eraser experiment, only 50% of the time 'information' would be erased - if that was the option chosen.

On page five of the PDF, there seems to be some form of explanation as to why this is, but I don't understand it. Is someone please able to explain why you would not get a detection of a photon from one of the cavities 50% of the time if you chose to 'erase the which-way information'?

Thanks!

Stevie

 

[DrChinese]

Without looking at the article: Erasers usually require coincidence matching to demonstrate that erasure has occurred. So there will be a background of items that do not quality for erasure because of the path they took prior to detection.

If there were some magical way to make those pairs disappear, it might be possible to send an FTL signal. So surprise! Nature has a way of correcting for this.

 

[StevieTNZ]

Hmmm, would there have been 100% information erasure in the experiment by Herzog, Kwiat, Weinfuter and Zeilinger (back in 1995)? I'm guessing with the erasure of idler which-path info, but then the regaining of that information through signal which-path information, then the erasure of signal which-path info, all idler and signal photon info is erased?

 

[StevieTNZ]

Another question:

http://books.google.co.nz/books?id=mQHswDNUbvMC&lpg=PP1&dq=The%20Demon%20and%20the%20Quantum&pg=PA128#v=onepage&q&f=false

I'm going to go a step further and discuss with the experimental set-up
in the picture link above in mind, what if we chose to find out which-way
info, so we open one shutter and either a click or no click occurs. But we
as humans don't find out which happened, and somehow managed to open the
second shutter therefore not being able to know which cavity the photon
came from (maybe have a counter that registers and displays a 1 (hidden
from us upon the first shutter opening - has no way of telling the time
the counter displayed a 1, etc. a device that nothing could tell when the
1 was displayed as each shutter was opened individually), and then if we
open the 2nd shutter, either the counter will stay at 1, or go to 1,
depending whether or not the photon was in the first cavity or not).
Because in principle we open a shutter and hear a click 100% of the time
if we decide to find out which-way info (other than 50% click, 50% no
click, i.e. we open one shutter 50% of the time and a photon is registered
every time, we open the other shutter 50% of the time and a photon is also
registered each time) then with one shutter open, THEN opening the other,
because 100% of the time we know we could get a photon detected when we
open only one, by having both opened, then we are unsure which cavity the
photon came from. What we would do then is correlate the points on the
screen with where we opened the top shutter first, bottom shutter second,
and vice versa (much like the correlation of points in the image link I
provided - hearing a click when opening both shutters at the same time,
not hearing a click when both shutters are opened at the same time -
because of the destructive interference of the photons from both
cavities).
Would interference result if we did what I've just explained? Would the
interference pattern be the same as that shown in this link: http://books.google.co.nz/books?id=mQHswDNUbvMC&lpg=PP1&dq=The%20Demon%20and%20the%20Quantum&pg=PA131#v=onepage&q&f=false (so finding out which-way info so to speak, i.e just open one
shutter, would not result in a definite path pattern, because we're going
to erase it - much like what I said in the beginning, the particle never
went along one path before the eraser of information because then
interference could not result after. It is also we when we become
conscious of which-way the particle went we can speak of the particle
going along that slit, otherwise if we don't become conscious of that
info, then erase what we could potentially find out, interference results.
The particle never went through one slit when we had the potential of
finding which-way info. It seems we must know the which-way info, not have
the potential to know the which-way info, for the particle to have gone
through one slit.

 

[StevieTNZ]

Would one achieve interference if the experiment was set up like this: http://books.google.co.nz/books?id=mQHswDNUbvMC&lpg=PP1&dq=The%20Demon%20and%20the%20Quantum&pg=PA129#v=onepage&q&f=false , but the shutters out? Would that interference be like the typical double-slit experiment (rather than the interference from correlation after erasure)?