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?

Today, Sekasti and co lay out the various methods for transferring or cloning the entanglement from one of a pair of entangled photons to an ensemble of at least 7 photons, which would be large enough for a human to see. In such an experiment, a human eye would detect this handful of photons while a conventional single photon detector spots the other photon.

The question is whether the entanglement between the original pair of photons is preserved in this new ensemble in a way that allows a measurement that can only be explained in terms of a superluminal influence.

Their conclusion is that such a measurement is still possible but within certain limits. Sekatski and co say that the data only allows conclusions to be drawn about the initial 2-photon pair. But the bottom line is that it is definitely possible for a real person to see quantum correlations with the naked eye.

Of course, there are other ways to generate entangled ensembles which would give a different, perhaps better result and no doubt Sekatski and co will look at those in due course.

In the meantime they are pressing ahead with the experiments described here. “The experimental realizations of the analyzed situations, using the various cloners, are underway and will be discussed in future works,” they say.

This falls short of actually entangling two humans but instead entangles a human and a photon detector.

Entangling a human with a lump of silicon and a few wires may not be as romantic as connecting with another soul but it will be remarkable to see it done at all.

Expect a successful result to generate a blaze of publicity.

Ref: arxiv.org/abs/1005.5083: Cloning Entangled Qubits to Scales One Can See