Leiden physicists entangle four rotating photons

February 3, 2016, Leiden Institute of Physics
Leiden physicists sent short ultraviolet laserpulses of two picoseconds through a crystal. This leads to the creation of four photons that are entangled in their orbital angular momentum—here depicted as red blue spirals. The rainbow colored circles illustrate the phase (color) and intensity (brightness) of the photon’s cross section. Credit: Leiden Institute of Physics

For the first time, scientists have entangled four photons in their orbital angular momentum. Leiden physicists sent a laser through a crystal, thereby creating four photons with coupled 'rotation'. So far this has only been achieved with two photons. The discovery makes uncrackable secret communication of complex information possible between multiple parties. The report is forthcoming in Physical Review Letters.

Entanglement holds great promise for perfectly secret communication and quantum computing. If two are created simultaneously, they are counterparts—their rotation is always reversed with respect to the other. If we measure left rotation for one photon, then the other will always rotate to the right after measurement with a similar filter. This is called entanglement. Before the measurement, each photon's rotation is undetermined.


Such rotation is a property of photons that scientists discovered in 1992 in Leiden; physicists call this orbital angular momentum. And this property has more than two values. It covers an infinitely large alphabet of information. Via rotation, it is possible to transfer much more information per photon than with a property like polarization, which contains only two possible values. In 2001, scientists managed to entangle two photons in orbital angular momentum for the first time. Now, Leiden physicist Wolfgang Löffler and his colleagues are the first to entangle four photons in this way. The discovery offers additional possibilities, like sending an uncrackable encrypted message to more than one party.


During their successful experiment, the researchers sent short ultraviolet laser pulses of two picoseconds through a crystal. Occasionally, this leads to the creation of four . This is extremely rare, but by generating 80 million pulses per second, they managed to detect on average two so-called photon quadruplets each second. To confirm these were, indeed, entangled in , the team used a spatial phase modulator that converts this back to light traveling as a plane wave. They registered this 'normal' light with single photon detectors.

Explore further: Disentangling information from photons

More information: Observation of four-photon orbital angular momentum entanglement, B. C. Hiesmayr, M, J. A. de Dood, W. Löffler, Physical Review Letters, 2016. On Arxiv: arxiv.org/abs/1508.01480

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not rated yet Feb 05, 2016
Huh? The field is continuous. The photons are not separable. They belong to the surface about the radiant field wither a directed filed of a beam or a plane wave. This states the ability to add a discontinuity to the field. Possible, but not spinning photons. Very poor interpretation. Not even sure there is a science of photons, the concept is very vague in description. Waves have no particles, less we define an effect upon a medium; but, then that's the medium.
Whydening Gyre
not rated yet Feb 05, 2016
This is not "entanglement". It's "symmetrical cloning".
Feb 06, 2016
This comment has been removed by a moderator.
3 / 5 (1) Feb 06, 2016
This is not "entanglement". It's "symmetrical cloning".

What is symmetrical cloning? Can't find that (aside from in a biological context)

And since they didn't clone the original photon it's not cloning in any case
not rated yet Feb 07, 2016
I love how so many people in the comments section are now experts in entanglement. Please address all rebuttals to PRL not the comments section of a science news website.
Whydening Gyre
not rated yet Feb 07, 2016
This is not "entanglement". It's "symmetrical cloning".

What is symmetrical cloning? Can't find that (aside from in a biological context)

And since they didn't clone the original photon it's not cloning in any case

Sorry, AA. and Dantoz. Was knee jerk reaction to what it appears like in the picture. It looks like they are just mini representations of a larger wave. I threw in the symmetrical part cuz there were two each of opposite chiralities. After attempting to understand the arxiv paper, I realize it is way over my head...

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