Can one see entanglement ?

Authors: Nicolas Brunner, Cyril Branciard, Nicolas Gisin

(Submitted on 4 Feb 2008 (v1), last revised 13 Nov 2008 (this version, v2))

Abstract: 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.

Submission history

From: Nicolas Brunner [view email]
[v1] Mon, 4 Feb 2008 18:34:26 GMT (100kb)
[v2] Thu, 13 Nov 2008 16:06:18 GMT (103kb)

http://arxivblog.com/?p=294

When humans become entangled

March 3rd, 2008 | by KFC |

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.

“Thus entanglement could in principle be seen,” conclude the group.

That’s a loaded statement if ever there was one. It implies that two humans could become entangled, if only for a brief moment.

Unfortunately, there is no room in the paper to discuss what “mantanglement” would be like. How long would Alf and Bess be mantangled? For as long as entangled photons bombard their retinas or longer? What would Alf and Bess feel?

I wonder if Gisin, Brunner and Branciard already know the answer to these questions, and whether we’ll be hearing some more interesting news from the Gisin lab in the months to come.

Ref: arxiv.org/abs/0802.0472: Can one see entanglement?

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http://arxivblog.com/?p=1230

Human eye could detect spooky action at a distance

February 19th, 2009 | by KFC |

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 Universityof 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.

But the work raises an obvious question: why is Gisin pursuing this line? The human eyeball could be put to use in plenty of optics experiments, so why the focus on mantanglement?

Could it be that Gisin thinks there is more to entanglement than meets the eye?

Ref: arxiv.org/abs/0902.2896: Quantum experiments with human eyes as detectors based on cloning via stimulated
emission