TR: How to Entangle Humans (contd)

[bystander]

How to Entangle Humans (contd)
the physics arXiv blog - 01 June 2010

An experiment in which humans will 'see' entanglement is pressing ahead.

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We've looked before at the extraordinary effort to entangle humans going on at the University of Geneva in Switzerland. Today we get a little more insight into the challenges this team faces in achieving their task.

In essence, entanglement is measured by creating two entangled photons, sending them to widely separated detectors and determining how quickly a measurement on one influences the other. If this influence is superluminal, then you've got entanglement on your hands.

The experiment underway by Pavel Sekatski and pals at the University of Geneva is simply to replace the photon detectors in this set up with human eyes.

That's not quite as ridiculous as it sounds. Human eyes are remarkably sensitive: they can be triggered by the presence of only a handful of photons. They have an efficiency of about 7 per cent, meaning that more than 90 per cent of the photons are lost as they travel between the pupil and the retina. They also have a dark count close to zero meaning that they generate few if any false positives.

That's not bad. In principle, human eyes ought to function quite well as detectors in these kinds of entanglement experiments.

But there's a problem: the number of photons needed to trigger detection, which is about 7 in humans. How do you reliably entangle at least this number of photons and still carry out the necessary tests?

Cloning Entangled Qubits to Scales One Can See

• arXiv.org > quant-ph > arXiv:1005.5083 > 27 May 2010

By amplifying photonic qubits it is possible to produce states that contain enough photons to be seen with a human eye, potentially bringing quantum effects to macroscopic scales. In this paper we theoretically study quantum states obtained by amplifying one side of an entangled photon pair with different types of optical cloning machines for photonic qubits. We propose a detection scheme that involves lossy threshold detectors (such as human eye) on the amplified side and conventional photon detectors on the other side. We show that correlations obtained with such coarse-grained measurements prove the entanglement of the initial photon pair and do not prove the entanglement of the amplified state. We emphasize the importance of the detection loophole in Bell violation experiments by giving a simple preparation technique for separable states that violate a Bell inequality without closing this loophole. Finally we analyze the genuine entanglement of the amplified states and its robustness to losses before, during and after amplification.

Human eye could detect spooky action at a distance
the physics arXiv blog - 19 Feb 2009

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  Human Entanglement

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It’s almost a year since Nicolas Gisin and colleagues at the University of Geneva announced that they had calculated that a human eye ought to be able to detect entangled photons. “Entanglement in principle could be seen,” they concluded.

That’s extraordinary because it would mean that the humans involved in such an experiment would become entangled themselves, if only for an instant.

Gisin is a world leader in quantum entanglement and his claims are by no means easy to dismiss.

Now he’s going a step further saying that the human eye could be used in a Bell type experiment to sense spooky-action-at-a-distance. “Quantum experiments with human eyes as detectors appear possible, based on a realistic model of the eye as a photon detector,” they say.

One problem is that human eyes cannot se single photons–a handful are needed to trigger a nerve impulse to the brain.

That might have scuppered the possibility of a Bell-type experiment were it not for some interesting work from Francesco De Martini and buddies at the University of Rome, pointing out how the quantum properties of a single particle can be transferred to an ensemble of particles.

That allows a single entangled photon, which a human eye cannot see, to be amplified into a number of entangled photons that can be seen. The eye can then be treated like any other detector.

This all looks like fun. The first person to experience entanglement –mantanglement–would surely be destined for some interesting press covereage.

Quantum experiments with human eyes as detectors based on cloning via stimulated emission

• arXiv.org > quant-ph > arXiv:0902.2896 > 17 Feb 2009

We show theoretically that the multi-photon states obtained by cloning single-photon qubits via stimulated emission can be distinguished with the naked human eye with high efficiency and fidelity. Focusing on the "micro-macro" situation realized in a recent experiment [F. De Martini, F. Sciarrino, and C. Vitelli, Phys. Rev. Lett. 100, 253601 (2008)], where one photon from an original entangled pair is detected directly, whereas the other one is greatly amplified, we show that performing a Bell experiment with human-eye detectors for the amplified photon appears realistic, even when losses are taken into account. The great robustness of these results under photon loss leads to an apparent paradox, which we resolve by noting that the Bell violation proves the existence of entanglement before the amplification process. However, we also prove that there is genuine micro-macro entanglement even for high loss.

When humans become entangled
the physics arXiv blog - 03 March 2008

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  Human Entanglement

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Something curious is happening at Nicolas Gisin’s lab at the University of Geneva. Gisin is a world expert in entanglement, the ghostly quantum phenomenon in which two or more particles become so deeply linked that they share the same existence, even when far apart.

Entanglement is now a routine resource in many labs: it can be generated, studied and even passed from one particle to another. It is usually measured using two detectors–Alice and Bob in the lingo of quantum physicists–which analyse pairs of incoming photons to see whether there is any spooky-action-at-a-distance, as a Einstein called it. In these so-called “Bell experiments”, spooky action rules.

Given the amazing properties of entangled photons, it was never going to be long before curious postdocs pointed these photons on themselves, in the manner of Nobel Prize winning Barry Marshall who famously swallowed H Pylori bacteria to see if it gave him ulcers, or more fittingly like Jeff Goldblum in The Fly.

What would happen if two humans–let’s call them Alf and Bess–replaced the lifeless Alice and Bob?

I guess most physicists would say that the process of observation in the eye is macroscopic, it involves large numbers of photons, and so any quantum effects would be drowned out.

Not so, reckons Gisin. It has long been known that the eye is sensitive enough to detect a mere handful of photons. He and a couple of pals, Nicolas Brunner and Cyril Branciard, have calculated that, were the eye a lifeless detector, it could be used to carry out the kind of Bell experiments described above.

Can one see entanglement?

• arXiv.org > quant-ph > arXiv:0802.0472 > 04 Feb 2008 (v1), 13 Nov 2008 (v2)

The human eye can detect optical signals containing only a few photons. We investigate the possibility to demonstrate entanglement with such biological detectors. While one person could not detect entanglement by simply observing photons, we discuss the possibility for several observers to demonstrate entanglement in a Bell-type experiment, in which standard detectors are replaced by human eyes. Using a toy model for biological detectors that captures their main characteristic, namely a detection threshold, we show that Bell inequalities can be violated, thus demonstrating entanglement. Remarkably, when the response function of the detector is close to a step function, quantum non-locality can be demonstrated without any further assumptions. For smoother response functions, as for the human eye, post-selection is required.

[bystander]

Can Physicists Make Quantum Entanglement Visible to the Naked Eye?
Discover Blogs | 80beats | 06 June 2010

A pair of quantum entangled photons sure makes a cute couple. Of course, the two might have opposite states – one might be spin up and another spin down, for example – but they promise they'll always stay that way.

They're also fiercely loyal, respecting their opposite-spin preferences no matter how long-distance their relationship. (That means that by checking the state of one entangled photon, you can instantly know the state of the other, distant photon, a handy way to "teleport" information.) Unfortunately, because the couple is merely two light particles, their shining example of old romance has been too dim for our eyes to see.

Until now. As announced in their recently published arXiv.org paper, physicists led by Nicolas Gisin at the University of Geneva in Switzerland believe they have found a way to watch this love affair unfold: by boosting the light emitted by one member of a quantum entangled pair, they think they can make this quantum effect visible to a human eye.

Measuring quantum states such as spin up or spin down is like looking at whether a switch is on or off. This closely matches the concept of a bit, a single 1 or 0, in computing. With entangled photons, physicists call these on/off states quantum bits or "qubits". What an observer would see while observing an entangled photon is really a choice between two states. The observer could then confirm entanglement by checking to see that the photon was loyal to its partner.

In the traditional set-up, two widely separated particle detectors are used to measure the entanglement of the two photons. But Gisin and his colleagues want to let the human eye do some of the work.

The researchers would send one photon to a standard detector and the other to a human observer in a dark room. The human would see a dim point of light in either the right or left field of view, depending on the photon’s quantum state. If those flashes of light correlate strongly enough with the output of the ordinary photon detector, then the scientists can conclude that the photons are entangled. [Wired]

But since the human brain won't register the flash caused by one single photon, researchers need to increase the light coming to a person's eye. More light requires more photons, but the original entanglement was a monogamous relationship. Gisin's team proposes entangling a group of similar state photons with one member of the pair, creating enough light for a person to see.

First, Gisin and his colleagues will entangle a pair of photons, and then amplify these signals by entangling each of these photons with another ensemble of, say, 100 photons. In the arrangement they are currently developing, one pulse of photons would then be sent at a person, whereas the other would be sent at a conventional photon detector to test what the volunteer saw, Gisin says. [Scientific American]

The observer sees the group – what the researchers call a "macroscopic" qubit. One photon entangles with a second, and that second with the group. Though the observer won't directly see the relationship between the first two photons, the second's romantic indiscretions, it's entanglement with the hoard of 100 or so photons, will be impossible to miss.

This probably won't lead to any big scientific breakthroughs, Gisin admits.

“Why do we do it nevertheless?” he says. “We find entanglement fascinating.” [Wired]

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How to See Quantum Entanglement
Wired - 02 June 2010

Human eyes can detect the spooky phenomenon of quantum entanglement — but only sometimes, a new study on the physics preprint website arXiv.org claims. While eyes can help determine if two individual photons were recently entangled, they can’t tell if the brighter bunch of photons that actually hit the retina are in this bizarre quantum state.

“In general you think these quantum phenomena that involve only a few particles, they’re really far removed from us. That is actually not so true anymore,” said physicist Nicolas Brunner of the University of Bristol. “You could really go to an experiment by just having people look at these photons, and from there really actually see entanglement.”

In an earlier paper, Brunner and colleagues at the University of Geneva in Switzerland sketched out an experiment in which a human observer could replace a standard quantum detector. This isn’t as far-fetched as it sounds, they say, because the eye’s most important job is to be a sensitive photon detector.

The researchers would first prepare two entangled photons — photons whose quantum properties are so intimately linked that one always knows what the other is doing. When an aspect of one photon’s quantum state is measured, the other photon changes in response, even when the two photons are separated by large distances.

The researchers would send one photon to a standard detector and the other to a human observer in a dark room. The human would see a dim point of light in either the right or left field of view, depending on the photon’s quantum state. If those flashes of light correlate strongly enough with the output of the ordinary photon detector, then the scientists can conclude that the photons are entangled.

“This is a standard way of measuring and detecting entanglement,” says physicist Nicolas Gisin of the University of Geneva, a coauthor of the new paper.

There’s just one problem: Humans can’t see individual photons. The retina needs at least seven photons to hit it at once before it sends signals to the brain. Also, 90 percent of photons are lost or scattered on the way through the gelatinous part of the eye to the retina. These restrictions mean that you need a lot of photons — at least hundreds, preferably thousands — to make a practical human quantum detector.

Spooky Eyes: Using Human Volunteers to Witness Quantum Entanglement
Scientific American - 03 June 2010

The mysterious phenomenon known as quantum entanglement—where objects seemingly communicate at speeds faster than light to instantaneously influence one another, regardless of their distance apart—was famously dismissed by Einstein as "spooky action at a distance." New experiments could soon answer skeptics by enabling people to see entangled pulses of light with the naked eye.

Although Einstein rebelled against the notion of quantum entanglement, scientists have repeatedly proved that measuring one of an entangled pair of objects, such as a photon, immediately affects its counterpart no matter how great their separation—theoretically. The current record distance is 144 kilometers, between the Canary Islands of La Palma and Tenerife.

Photons make up light—and the fact that scientists regularly entangle these tiny packets of energy raised the possibility that humans might actually be able to observe this effect. Now experiments to shoot entangled photons at the human eye are under development, and should take place later this year. "It's fascinating that entanglement is something we could see with the naked eye—it brings us closer to this strange quantum phenomenon," notes researcher Nicolas Gisin, a quantum physicist at the University of Geneva in Switzerland

Entanglement is measured by creating entangled particles, sending them to different detectors, and seeing how quickly a measurement on one influences the other. The idea for this experiment is simply to replace the photon detectors with human vision. Human retinas are surprisingly sensitive, capable of being triggered by roughly seven photons. And although they only have an efficiency of about 7 percent (of every 100 photons that enter the pupil, only about seven go on to reach the retina) they have a dark count of virtually zero, meaning they generate few if any false positives.