Physicists Explain How Human Eyes Can Detect Quantum Effects

Sep 29, 2009 By Lisa Zyga feature
How human eyes could detect quantum entanglement: A single-photon qubit is amplified through cloning via stimulated emission in a nonlinear crystal (red box). The clones are split into two orthogonal polarization modes, with the polarization basis varied with the help of a wave plate (green box). Each mode is then detected by a naked human eye. Image credit: Pavel Sekatski, et al.

( -- By greatly amplifying one photon from an entangled photon pair, physicists have theoretically shown that human eyes can be used as detectors to observe quantum effects. Usually, detecting quantum phenomena requires sensitive photon detectors or similar technology, keeping the quantum world far removed from our everyday experience. By showing that it’s possible to perform quantum optics experiments with human eyes as detectors, the physicists can bring quantum phenomena closer to the macroscopic level and to everyday life.

The group of physicists is from the University of Geneva, and includes Pavel Sekatski, Nicolas Brunner (also from the University of Bristol), Cyril Branciard, Nicolas Gisin, and Christoph Simon. In their study published in a recent issue of Physical Review Letters, the scientists theoretically show how human eyes can be used to detect a large Bell inequality violation, which proves the existence of .

As the physicists explain, the key to achieving detection of quantum effects is to use the process of quantum cloning by stimulated emission. Recently, using quantum cloning, researchers in Rome have experimentally created tens of thousands of clones starting from a single-photon. Then, by amplifying one photon of an entangled pair, the researchers managed to demonstrate entanglement. In order to do this, specific detectors are required, which can distinguish two orthogonal amplified states with a high success rate.

Now, what Sekatski and co-workers have shown is that the human eye performs extremely well at the task of distinguishing between orthogonal amplified states. This is a consequence of the eye's main characteristic, namely as a detection threshold. Below a certain threshold number of incoming photons, the eye remains blind (no light is seen), whereas above the threshold the efficiency (i.e. the probability of seeing) is close to one.

In their calculations, the authors also considered the influence of experimental imperfections, such as photon losses, which are inevitable in a real experiment. They found that the setup is surprisingly robust. A strong Bell violation can be obtained even in case of high losses, demonstrating the presence of entanglement. This is a very astonishing feature since entanglement is generally an extremely fragile property, highly sensitive to experimental imperfections such as losses.

To solve this apparent paradox, the scientists uncovered a loophole in the system. They showed that a specific multi-photon state could actually behave exactly as the entangled state. Therefore, the high Bell violation actually witnesses the entanglement of the original photon pair, i.e. before the amplification occurs, but not the entanglement between the amplified state and the single photon. Still, the authors show that the amplified state and the single photon are nevertheless entangled, but revealing this entanglement would require more sophisticated measurements. This subtle issue provides a much better understanding of the quantum nature of amplified states, which were recently the subject of a controversy among the scientific community.

As the researchers finally note, using human eyes as detectors in actual quantum experiments will face significant technical challenges. However, the possibility of observing quantum effects directly with our own eyes is fascinating. Naked eye observation would bring the observer one step closer to the quantum world.

“From our theoretical study, the experimental perspectives appear very promising,” Brunner told He added that, although there will be many technical challenges, Nicolas Gisin’s research group in Geneva has already started working on experiments.

More information: Pavel Sekatski, Nicolas Brunner, Cyril Branciard, Nicolas Gisin, and Christoph Simon. “Towards Quantum Experiments with Human Eyes as Detectors Based on Cloning via Stimulated Emission.” 103, 113601 (2009).

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User comments : 19

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not rated yet Sep 29, 2009
Does this imply that quantum waveform collapse does not need a sentient observer/measurer after all? (Unless backed up by a physics lab.)
not rated yet Sep 29, 2009
If you want to observe some really neat quantum effects, all you have to do is look at the back of an ordinary CD.
Sep 29, 2009
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not rated yet Sep 29, 2009
quantum waveform collapse does not need a sentient observer/measurer
Naw as I understand it 'observing' a particle means bouncing something off of it, which will necessarily affect it. We observe macroscopic objects the same way, but prodding or shining light on them does not necessarily affect them. This much of QM I understand (maybe?)(except that 2 slit/1 particle thing)
2.4 / 5 (5) Sep 29, 2009
Bohm's addition of the Quantum Potential Term to the Schrodinger wave equation proves that it is INFORMATION and not observation (think Schrodinger's Cat) that collapses the superposed spectrum of quantal evolutionary phase-states. BTW, it is theoretically accepted that the human eye can "see" as little as six photons at a time (the photon-multiplier chain in the eye is of enormous amplification magnitude, has two stages and controlled by an oscillatory biochemical timer for stability.) Although these experiments are interesting I think that it however amounts to somewhat reductionistic science... Rather have a look at Prof. Albrecht Buehler's cellular intelligence and proven cellular photonavigation via near infrared biophotons - a little more interesting and certainly of more profound import.
2.6 / 5 (5) Sep 29, 2009
I'll take this down fantasy land for a moment...if the eye can perceive quantum events, does that explain those annoying people on the Discovery Channel that claim to see visions of airplanes falling out of the skies? people knowing they won the lottery? etc?
1 / 5 (3) Sep 30, 2009
This article is entirely bogus. Proof: try following their picture. Take a large prism, and align it so that one eye looks vertically and one horizontally. That is impossible (due to physiological constraints)!
Sep 30, 2009
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not rated yet Sep 30, 2009
What an interesting schema cognition circuit for experimentation in cybernetics reversing the flow of information in it. We can clone information matter but not a spirit.
not rated yet Sep 30, 2009
But if the state of the photon is in a superimposed state, then it cannot be cloned. (Google "No-cloning theorem") What gives?
not rated yet Sep 30, 2009
The same article (via Google "no-cloning theorem") says "it is possible to produce imperfect copies" .... "This can be done by coupling a larger auxiliary system to the system that is to be cloned, and applying a unitary transformation to the combined system".

But what is an "imperfect" copy in a binary quantum system? An imperfect copy of a 1 is a 0. So that is a big error, whereas the phrase "imperfect copy" makes it seem like it is a workable version? Or perhaps is it making 100 copies where 99 are 1 (correctly)and one is 0 (incorrectly)?
not rated yet Sep 30, 2009
First of all, if we are talking about a state which is superimposed, it is not in either |0> or |1>, but in a state a|0> + b|1>, where a^2 + b^2 =1: in other words, it is in a state where it has a probability of it being 0 when measured, and a probability of being 1 when measured. So, an imperfect copy would be c|0> + d|1>, where c is not equal to a, and d is not equal to b.
not rated yet Sep 30, 2009
You are correct. I need to re-think as I was writing quantum state while meaning collapsed state of 0 or 1.

Even if the probability of a photon collapsing into state 1 was more likely than into state 0, the probability element still means that one is unsure what is going to be the collapsed state until after the collapse event. No wonder cloning is "imperfect". Even a 'perfect' clone will not necessarily collapse the same way as the original. (At least I doubt it.) But I suppose that if you get 75% (say) success on uniformity of direction of collapse then the clone is reasonably good. I wonder what the success rate is?
not rated yet Sep 30, 2009
LOL this is accomplished as easily as resting the neck of a guitar on one of your shoulders and looking at the strings, since your eyes have different disposition the strings will cross out and look like X's
not rated yet Sep 30, 2009
A second thing that is odd about the set-up is that it refers to ENTANGLED particles, not clones. Yet the whole experiment is "cloning" a single photon. What I think the author meant is that the photon goes through a beam splitter that would create two particles whose polarizations are entangled. Obviously the diagram simplifies angles. Other comments:
to TegiriNenashi: the eyes can be two observers, and
to ben 6993: they need not be eyes -- collapse or splitting into worlds (whichever) does not depend on sentience.
Finally, Mercury_1 is correct: an understanding of quantum effects will show that they are all around you.
not rated yet Sep 30, 2009
If I understand correctly, if there were enough photons, the vertically (therefore collapsed) polarized photons could be passed through a red glass (to hopefully turn them red? {the redness is my idea, not in the article}) and recombined with the horizontally polarized (therefore collapsed) photons. And a pink mix obtained. We could have a redness colour coded scale that would give you the vert and horiz components of probability in the uncollapsed photon. Like a litmus test.
not rated yet Sep 30, 2009
I think what is happening is that one un-collapsed photon is used to make many un-collapsed clone photons. (That part is a black box operation to me.) Once you have all these clones available, you can collapse them. Collapsed photons come in two varieties according to their polarisation. So you can turn them into two streams of photons, one stream for each polarisation. Though the two streams are filled with collapsed photons, the quantities of photons should represent the original photon's two quantum state probabilities. Outcome state on collapse is not purely chance, although there will be a chance element to it, it should be correlated to the probs in the QM states of the original photon.
Oct 01, 2009
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not rated yet Oct 01, 2009
No matter how small the puzzle nor how many pieces, without order there is no complete picture. Though we may envision the result with pieces missing,the ever changing picture adds more pieces. Time frame contingency altering the pov and understanding of endless possibilities in time. I'd have to guess that "What you see is, What you get" being time limited.
not rated yet Oct 01, 2009
This article is entirely bogus. Proof: try following their picture. Take a large prism, and align it so that one eye looks vertically and one horizontally. That is impossible (due to physiological constraints)!

Umm... the diagram is drawn as would a diagram of electronic circuitry. It's not a visually correct diagram of the actual shape of the device, or schema, but exagerated so the functions of each component are clear.
not rated yet Oct 04, 2009
How did they "un-collapse" the fotòn?
1 / 5 (1) Oct 05, 2009
It would be strange if we evole to see quantum energy.