

Entangled Photons Make a Picture from a Paradox - foolrush
http://www.scientificamerican.com/article/entangled-photons-make-a-picture-from-a-paradox/

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dchichkov
"""

    
    
      One advantage of the technique is that the two photons
      need not be of the same energy, Zeilinger says, meaning
      that the light that touches the object can be of a
      different colour than the light that is detected. For
      example, a quantum imager could probe delicate biological
      samples by sending low-energy photons through them while
      building up the image using visible-range photons and a
      conventional camera. The work is published in the August
      28 issue of Nature.

~~~
bane
Would this mean then that I could "image" something with a wavelength that
makes things like walls, clothes or skin transparent and then see them with
visible wavelengths? For example, use entangled infrared photons to see
through water vapor (clouds) but end up with visible wavelength images of my
subject?

My thinking are implications in satellite imaging, security, medicine, etc.

(I have basically a caveman understanding of this topic, so clarification
would be helpful)

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tucif
The preprint of the paper is avalable on the arxiv, in case you don't have a
Nature subscription:
[http://arxiv.org/abs/1401.4318](http://arxiv.org/abs/1401.4318)

------
axilmar
The first paragraph of the article says:

"Physicists have devised a way to take pictures using light that has not
interacted with the object being photographed."

Then in another paragraph it says:

"In the first path, one photon in the pair passes through the object to be
imaged"

So the light actually has interacted with the object to be photographed. The
opening paragraph is obviously wrong.

Furthermore, another paragraph says:

"In ghost imaging, even though only one photon interacts with the object, both
photons need to be collected to reconstruct the image, whereas in the Vienna
team's work only one photon needs to be detected"

Then another one says:

"The remaining photon from the second path is also reunited with itself from
the first path and directed towards a camera"

So again, the article contains a huge ambiguity, because in one paragraph it
says that only one photon is needed for the photograph and then it says that
one photon needs to be reunited with another photon (even if they are
entangled, they are still different photons), so two photos are needed for the
photograph.

~~~
JoeAltmaier
Are they entangled, or just potential photons? When splitting light, photons
go 'both ways' potentially even though is a classical sense there is only 1
photon that will ever be detected. Recombining them is still meaningful in a
wave sense, because each potential photon path interacts with the other when
the paths are reunited.

------
teekert
But what if I keep the entangled photon around for very long while separating
the two by a large distance. Then I image the cat using the photons I kept
around which forms a cat image at the very large distance. Very spooky action.

Or is this not the way this works? Are the entangled pairs not actually used
to build the image? I find it difficult to understand what they do exactly
although the Nature site seems pretty clear:

"This form of imaging uses pairs of photons, twins that are ‘entangled’ in
such a way that the quantum state of one is inextricably linked to the other.
While one photon has the potential to travel through the subject of a photo
and then be lost, the other goes to a detector but nonetheless 'knows' about
its twin’s life and can be used to build up an image."
([http://www.nature.com/news/entangled-photons-make-a-
picture-...](http://www.nature.com/news/entangled-photons-make-a-picture-from-
a-paradox-1.15781))

------
DanGPhoton
About 15 years ago I saw Paul Kwiat at UIUC give a talk on "Interaction Free
Measurements" which seems to be effectively the same thing as here. (cf
[http://physics.illinois.edu/people/kwiat/interaction-free-
me...](http://physics.illinois.edu/people/kwiat/interaction-free-
measurements.asp) ) I could never figure out why this did not get more
attention at the time

~~~
pyre
Is this really "Interaction Free"? You're hitting it with photons. They
comment on using low-energy photons, but that just minimizes the interaction,
while still producing something useful (visible spectrum image).

------
shadowmint
If this works as described I wonder if it could be used to distinguish
incoming scattered entangled photons from other incoming 'noise' photons.

That would be a really exciting application for imaging in noisy envrionments.

------
mabbo
This being hacker news, I can't help but wonder about the implications for
quantum computing. Maybe this is already an answered question, but can one
read a Q-bit without interaction that might break it's entanglement?

~~~
ClayFerguson
As far as I have ever heard, you must collapse the wave function to measure a
Q-bit, and that is when entanglement always stops. However if we can create
systems where a collapse can always 'retrigger' a new entanglement we could
theoretically create computers that run at the Planc Time as the clock rate,
but we don't know how to do that yet. That's decades off, or centuries.

------
probablyfiction
"Spooky action" indeed

~~~
lisper
It actually isn't spooky at all once you understand it properly (but it is
almost never explained properly, especially in the popular press). Measurement
and entanglement are really the same phenomenon. The process of "measuring"
photon A was actually begun when it became entangled with photon B (and vice
versa). We call it a "measurement" when a large number of particles (like a
measurement apparatus or a brain) become mutually entangled with each other.
See:

[http://www.flownet.com/ron/QM.pdf](http://www.flownet.com/ron/QM.pdf)

for a more detailed explanation.

~~~
ClayFerguson
lisper, actually measurement is the act of collapsing the wave, and
entanglement only exists before the wave function collapse. It's possible to
never measure something, and it could be entangled forever.

~~~
waqf
You didn't read lisper's link, did you?

~~~
ClayFerguson
Yes I read his comment. Both entanglement and measurement apply to individual
particles, so the opposite of what he said is true.

~~~
lisper
You didn't read waqf's comment, did you? You may have read my _comment_ but
you clearly didn't read my _link_.

> actually measurement is the act of collapsing the wave, and entanglement
> only exists before the wave function collapse. It's possible to never
> measure something, and it could be entangled forever.

Entangled particles continue to be entangled even after they are "measured".
If this were not true, faster-than-light communication would be possible. To
understand why, read the paper.

The only way to "undo" an entanglement is to time-reverse the process that
created the entangled pair to begin with, i.e. to bring the members of the
entangled pair back together.

~~~
ClayFerguson
You are correct, I didn't read your link. Why? Because every word of what you
said in your comment was wrong. So why _would_ I click the link?

~~~
lisper
I dunno, because you might learn something?

------
dang
Also [https://medium.com/the-physics-arxiv-blog/entangled-
photons-...](https://medium.com/the-physics-arxiv-blog/entangled-photons-
produce-quantum-images-of-invisible-targets-they-never-hit-97ea2d275eba) and
[http://spectrum.ieee.org/tech-
talk/semiconductors/devices/qu...](http://spectrum.ieee.org/tech-
talk/semiconductors/devices/quantum-entanglement-camera), via
[https://news.ycombinator.com/item?id=8234014](https://news.ycombinator.com/item?id=8234014)
and
[https://news.ycombinator.com/item?id=8234548](https://news.ycombinator.com/item?id=8234548)
respectively.

------
debt
The implications of faster than light communication should not be understated.
Using quantum entanglement, you could "send"(whatever that means) a text to
someone near Alpha Centari _faster_ than sending a text to someone in
Zimbabwe.

~~~
michael_nielsen
Please don't repeat this. It is false.

(For this kind of thing, stating credentials seems useful: I was a
professional quantum physicist for 13 years, much of that time spent working
on the theory of entanglement, and entanglement-based effects such as quantum
teleportation.)

~~~
debt
Why is it false then?

~~~
jmaygarden
Because both photons in the pair must be correlated. From the article:

"The remaining photon from the second path is also reunited with itself from
the first path and directed towards a camera, where it is used to build the
image, despite having never interacted with the object."

So, they need both the particles together. It doesn't work if one is near
Alpha Centauri and cannot be combined with the one on Earth. I'm a complete
layman, but this is my understanding of it.

Apparently, the breakthrough here is being able to use different wavelength
and intensity of light to interact with an object than that desired for
imaging. No information is actually transferred through entanglement.

~~~
sologoub
That's how I read this as well. That said, the medical applications are
amazing - they might be able to do MRI-like (or better?!) imaging without the
harmful effects!

~~~
roywiggins
MRI imaging is effectively harmless (unlike, say, CT scans, which might cause
harm).

