Picturing Schrodinger's cat: Quantum physics enables revolutionary imaging method

Aug 28, 2014
The cats represent the famous Schrödinger cat paradox, in which a quantum cat closed in a box can be dead and alive at the same time. The dark and light cat bodies are images of a cardboard cut-out. They arise due to destructive and constructive quantum interference, respectively. In this experiment the photons that interact with the cardboard cut-out are not detected, while the images are obtained by detecting only photons that never interact with the object. Credit: Gabriela Barreto Lemos

Researchers from the Institute for Quantum Optics and Quantum Information (IQOQI), the Vienna Center for Quantum Science and Technology (VCQ), and the University of Vienna have developed a fundamentally new quantum imaging technique with strikingly counterintuitive features. For the first time, an image has been obtained without ever detecting the light that was used to illuminate the imaged object, while the light revealing the image never touches the imaged object.

In general, to obtain an image of an object, one has to illuminate it with a beam and use a camera to sense the light that is either scattered or transmitted through that object. The type of light used to shine onto the object depends on the properties that one would like to image. Unfortunately, in many practical situations, the ideal type of light for the illumination of the object is one for which cameras do not exist.

The experiment published in Nature this week for the first time breaks this seemingly self-evident limitation. The object (e.g. the contour of a cat) is illuminated with light that remains undetected. Moreover, the light that forms an image of the cat on the camera never interacts with it. In order to realise their experiment, the scientists use so-called "entangled" pairs of photons. These pairs of photons - which are like interlinked twins - are created when a laser interacts with a non-linear crystal. In the experiment, the laser illuminates two separate crystals, creating one pair of twin photons (consisting of one infrared photon and a "sister" red photon) in either crystal. The object is placed in between the two crystals. The arrangement is such that if a photon pair is created in the first crystal, only the infrared photon passes through the imaged object. Its path then goes through the second crystal where it fully combines with any infrared photons that would be created there.

With this crucial step, there is now, in principle, no possibility to find out which crystal actually created the photon pair. Moreover, there is now no information in the infrared photon about the object. However, due to the quantum correlations of the entangled pairs the information about the object is now contained in the red photons - although they never touched the object. Bringing together both paths of the red photons (from the first and the second crystal) creates bright and dark patterns, which form the exact image of the object.

The cats represent the famous Schrödinger cat paradox, in which a quantum cat closed in a box can be dead and alive at the same time. The dark and light cat bodies are images of a cardboard cut-out. They arise due to destructive and constructive quantum interference, respectively. In this experiment the photons that interact with the cardboard cut-out are not detected, while the images are obtained by detecting only photons that never interact with the object. Credit: Gabriela Barreto Lemos

Stunningly, all of the infrared photons (the only light that illuminated the object) are discarded; the picture is obtained by only detecting the red photons that never interacted with the object. The camera used in the experiment is even blind to the infrared photons that have interacted with the . In fact, very low light infrared cameras are essentially unavailable on the commercial market. The researchers are confident that their new imaging concept is very versatile and could even enable imaging in the important mid-infrared region. It could find applications where low light imaging is crucial, in fields such as biological or medical imaging.

The cats represent the famous Schrödinger cat paradox, in which a quantum cat closed in a box can be dead and alive at the same time. The dark and light cat body outlines are images of an etched piece of silicon. They arise due to destructive and constructive quantum interference, respectively. In this experiment the photons that interact with the silicon are not detected, while the images are obtained by detecting only photons that never interact with the object. Credit: Gabriela Barreto Lemos


Explore further: 'Compressive sensing' provides new approach to measuring a quantum system

More information: "Quantum imaging with undetected photons": Gabriela Barreto Lemos, Victoria Borish, Garrett D. Cole, Sven Ramelow, Radek Lapkiewicz, Anton Zeilinger. Nature, 2014. DOI: 10.1038/nature13586

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antialias_physorg
4.4 / 5 (14) Aug 28, 2014
Woha. Can we transpose this to medical x-ray scanners where the part of the entangled pair that is actually passed through the body is of a less harmful frequency than the one that gives the actual image?
That would be huge.
Noumenon
4.5 / 5 (8) Aug 28, 2014
They could use that (lower) frequency to begin with anyway,..... the one actually chosen is so because it penetrates through flesh sufficiently. I think the benefit of the above remarkable experiment would be on the side of the detected photons.
mahi
1 / 5 (9) Aug 28, 2014
The same can be explained by the 'holographic property' of light waves without resorting to the mythical phenomena of quantum physics.

http://debunkingr...ectrons/
russell_russell
not rated yet Aug 28, 2014
Quantum superposition.

Question:
Where and at what point in this experiment is coherence lost?
Detection can not be the source of decoherence.

11791
5 / 5 (4) Aug 28, 2014
Schrodinger first wrote about his frigging cat in 1946. It must be dead of old age!
Mimath224
1 / 5 (1) Aug 28, 2014
@antialias_physorg yes, I agree with you but I seem to have missed the point of the title, that is, how will this show us that a real cat is in superposition of being both dead and alive?
dirk_bruere
not rated yet Aug 29, 2014
This was done years ago. researchers never seem to read the old literature
Vietvet
5 / 5 (3) Aug 29, 2014
This was done years ago. researchers never seem to read the old literature


Links?

Luten
1 / 5 (1) Aug 29, 2014
It's not an image by photons that never interacted with the object.
It's an image by ABSENCE of some photons - those that interacted with the object.
There is nothing new in it - it's known for a very long time and called "shadow".
antialias_physorg
4 / 5 (4) Aug 29, 2014
There is nothing new in it - it's known for a very long time and called "shadow".

Look at the images. The bright part is not a shadow - yet it is created by constructive interference from photons that never came close to the object.
Jaeherys
not rated yet Aug 29, 2014
Could someone explain this a bit more thoroughly to a poor old biologist? Does light still interact with the particles that make up the object to imaged? If it does how does this relate to Schrodinger's cat? Could this be used to improve the signal:noise ratio when imaging fluorophores at the the cellular level or I guess I should precede by asking, what would be the resolution of such a technology?
antialias_physorg
4.2 / 5 (5) Aug 29, 2014
Don't get hung on the "Schrödinger's cat" reference.

The gist of itis:
- create two entangled photons (one red, one infrared...but the actual color doesn't matter. It's just a way to make sure that you don't mix the two afterwards.)
- send one through the object but subsequently erase any information it is carrying (by cancelling it out with another photon created at the destination, so that you cannot tell which photon is which.) If you plot all these infrared photons you just get a uniform image - i.e.: no image information.

However the image information is retained in the red photons that didn't go anywhere near the object. The 'interaction' is via the entanglement.

Could this be used to improve the signal:noise ratio when imaging fluorophores at the the cellular level

This may be an interesting paper:
http://physicswor...distance
Though, as noted in the last pargraph - squeezed light may be better
Mimath224
not rated yet Aug 29, 2014
@antialias_physorg I find this very interesting as I could see all sorts of applications, well theoretically that is, back to 'Alice & Bob' eh? The link you provided was also interesting despite the comment from 'edkorczynski'. What is/would be the cost difference between the techniques?
Aligo
4.4 / 5 (7) Aug 29, 2014
Could someone explain this a bit more thoroughly to a poor old biologist?
This experiment has made a photo with using of entangled photon pairs. These photons were generated with excitation of nonlinear optical crystal, which generates one long-wavelength ("red") and one short-wavelength ("blue") photon at the same moment. These photons were separated spatially and one of them (this "red" one) has been used for creation of image by passing through cardboard mask with silhouette of cat. When both photons were recombined after then, then the image projected with recombined photon pairs reproduced the information collected and imprinted into red photons.
Could this be used to improve the signal:noise ratio when imaging fluorophores at the the cellular level
IMO not, but it could have another applications. For example the long-wavelength light passes well through tissue, but it's difficult to detect with cameras, which are sensitive to short-wavelength light instead.
Aligo
3.9 / 5 (7) Aug 29, 2014
The simplest interpretation of this experiment from AWT perspective is, that the photons do behave like the flying blobs of slightly more dense vacuum undulating in space similarly to the droplets inside of lava lamp. When one such a droplet gets separated into two parts, it maintains the character of surface vibrations for both halves of it. When one of halves changes its surface vibrations with interaction with observer, this change may get transferred into another half of droplet, once they merge again. In this way, both halves of photon pairs behave like having rudimentary memory of their past. At the case of photon, this information remembered and mediated is usually a phase shift between bulk and surface waves of photon, i.e. the spin (polarization). IMO we could realize a similar experiment with flying undulating droplets in microgravity arrangement. We could for example apply the ultrasound pulse to one of them and merge them. The vibrations will remain preserved in the merger.
russell_russell
5 / 5 (1) Aug 30, 2014
The simplest interpretation of this experiment from quantum physics are that correlations from "collapsed" states makes information gathered probable.

Entanglement has zero correlation to classical analogies and classical physics. See the "simplest interpretation" above.
Information was not created, destroyed, transferred, transmitted, preserved, remembered, mediated, maintained, merged, or changed in this experiment.

Yes you can increase the signal to noise ratio. The higher the gathered information correlates the higher the resolution.
russell_russell
not rated yet Aug 30, 2014
http://www.welt.d...ren.html

The "simplest interpretation" for lay folk. Words in quotations is where a concise, precise language is discarded for the sake of not losing the understanding from a readership in non-related fields of science and research.
antialias_physorg
5 / 5 (1) Aug 30, 2014
back to 'Alice & Bob' eh?

I've been trying to imagine how Eve could use this but have come to no definite conclusion. It still seems that quantumcryptographic exchanges would be secure (or at least noticeably disturbed) - even if Eve could look at the signal with the parts of entangled photon pairs of her own that don't actually interact with the signal itself.
There's still interaction via the photons that get the unrecoverable information (the infrared photons in the article), and that would show up

The simplest interpretation of this experiment from AWT perspective is,

Tsk tsk, Zeph...upvoting yourself via sockpuppets? I thought you had gone past that stage years ago. Pathetic, man...really pathetic.
Aligo
1 / 5 (2) Aug 30, 2014
I didn't vote anybody here, myself the less. But even if I would, it wouldn't explain, why the cited post didn't get any downvotes, as most of my posts here regularly do - don't you think? Maybe some glitch in PO matrix manifests itself here... Yea, it's pathetic...
Pierebean
not rated yet Aug 30, 2014
So only some infrared photons goes through the shadow mask cat? If the shadow mask is made out of silicon, provided that Si is transparent to
Infrared, is there an actual interaction of the infrared photon with the mask?

If yes, the interactions is only "transmitted" to the red-sensitive camera through the entanglement process, right?

If there is no such Si mask/IR photon interaction, then I don't understand.
Aligo
1 / 5 (1) Aug 30, 2014
The Si is still rather opaque to 810-nm light which has been used in this experiment. It's bandgap width1.12 eV corresponds the onset of absorption curve at 1100 nm. Silicon photocells typicaly operate at range from 400 to 1100 nm, so you can observe the infrared LED of remote control with your mobile phone camera (this diode operates at 810-nm wavelength too). If the silicon would be transparent for this light, you couldn't detect it with silicone CCD chip of camera.
Aligo
1 / 5 (1) Aug 30, 2014
BTW The two-color ghost imaging has experimentally demonstrated first by Karmakar et.al. (Prof. Shih' s group in University of Maryland Baltimore County) and they also predicted the real application of these ones. Check the publication and popular info about it)
Urgelt
5 / 5 (1) Sep 01, 2014
Auntie wrote, "...but the actual color doesn't matter. It's just a way to make sure that you don't mix the two afterwards."

Not true.

The infrared photons are ideal for scanning certain classes of objects, but we lack imaging CCDs for that range of frequencies.

The red photons are useless for scanning those classes of objects, but are easy to capture via imaging CCDs.

The selection of frequencies for the entangled photons is not arbitrary.

Further, *if* we could image the useful infrared frequencies directly, the entire experiment could be done in infrared - no red photon needed. Separation isn't accomplished by frequency diversity, but by the mechanics of the experiment.
antialias_physorg
not rated yet Sep 01, 2014
The infrared photons are ideal for scanning certain classes of objects, but we lack imaging CCDs for that range of frequencies.

The red/ionfrared mix was chosen because there is no chance that the detector would pick up any infrared photons afterwards (which wouuld put a questionmark on the results, since the scientists could then, in theory have been capturing stray infrared photons that directly interacted with the image)

They could as well have used blue and x-rays with an object that interacts with one of these wavelengths and a detector sensitive to only the other.

The particular mix (red/infrared) isn't important. What's important is that they are of different energies. (well, not even that is important: they could have used different polarisations with a detector selective for only one type of polarisation and get the same result).

It's just that red/infrared is an easier experimental setup, that's all.
antialias_physorg
3.7 / 5 (3) Sep 01, 2014
I didn't vote anybody here, myself the less

...Yeah. suddenly you get upvotes by people who haven't ever made any posts and all registered on the same day within 3 minutes of each other.

Very suble, that. Loser.
russell_russell
not rated yet Sep 01, 2014
De-coherence takes place with the detection (measure) of red photons from the recombined identical second split beam in the experiment.

Quantum photography has potential...to defeat cloaking.