Monday, September 30, 2013

The Light Saber: Solid Photons, Fact or Fiction?

The light saber. It looked magical when Obi-One Kenobi first whipped it out in the bar in the spaceport town of Mos Eisley on the planet Tatooine; light energy that has the solidity of matter and which can cut through anything. I never quite understood its usefulness in an advanced world with laser guns and intergalactic travel, but never mind. It was graceful, beautiful, a wonderful combination of old world elegance and new world technology. But it is a work of fiction that isn’t real, right? Right. Until now.

In a September 25 paper in Nature (1), a team of Harvard and MIT scientists have created a new state of light that has properties of matter, much like the light saber. Photons are normally without mass and they do not interact with other photons. In this study, though, two photons were fired through a cloud of cold rubidium atoms just a few degrees above absolute zero. As the photons passed through the cloud, they started interacting with the rubidium atoms in a series of exchanges of energy (an effect called the Rydberg blockade) resulting in the two photons exiting together as a single molecule, bound together into “polarization-entangled photon pairs” which acted as though they had mass.

Are there any practical applications? Yes, in quantum computers. But I am still holding out for my light saber.

1.     Ofer Firstenberg, Thibault Peyronel, Qi-Yu Liang, Alexey V. Gorshkov, Mikhail D. Lukin, Vladan Vuletić. Attractive photons in a quantum nonlinear medium. Nature, 2013; DOI: 10.1038/nature12512

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