The Experiment That Will Allow Humans to “See” Quantum Entanglement

We’ve puzzled over the nature of entanglement for almost a century. Now physicists have devised a way for us to “see” it for the first time.

Entanglement is the strange phenomenon in which two quantum particles become so deeply linked that they share the same existence. When this happens, a measurement on one particle immediately influences the other, regardless of the distance between them.

Entanglement has puzzled physicists for the best part of a century. At first, its very existence was disputed. But today, physicists create entangled particles in huge numbers in labs all over the world. They routinely use entanglement to send perfectly encrypted messages, to study quantum computation, and to better understand the nature of this profound phenomenon.

The ease with which particles such as photons can be entangled has led some physicists to ask an interesting additional question: will humans ever be able to “see” entanglement?

Today we get an answer thanks to the work of Valentina Caprara Vivoli at the University of Geneva in Switzerland a few pals. They’ve devised an experiment that should allow a human eye to directly detect entanglement. And they say the scene is now set for the first experiment of this kind.

Finding a way for a human eye to detect entangled photons sounds straightforward. After all, the eye is a photon detector, so it ought to be possible for an eye to replace a photo detector in any standard entanglement detecting experiment.

Such an experiment might consist of a source of entangled pairs of photons, each of which is sent to a photo detector via an appropriate experimental setup.

By comparing the arrival of photons at each detector and by repeating the detecting process many times, it is possible to determine statistically whether entanglement is occurring.

It’s easy to imagine that this experiment can be easily repeated by replacing one of the photodetectors with an eye. But that turns out not to be the case.

The main problem is that the eye cannot detect single photons. Instead, each light-detecting rod at the back of the eye must be stimulated by a good handful of photons to trigger a detection. The lowest number of photons that can do the trick is thought to be about seven, but in practice, people usually see photons only when they arrive in the hundreds or thousands.

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