Scientists have created a hitherto unseen form of matter




Working with colleagues from the Center for ultracold atoms Harvard-MIT, a group led by Harvard professor of physics Mikhail Lukin and professor of physics at the Massachusetts Institute of Technology, Vladan Vuletic was able to link the photons together to form a molecule – a state of matter, until recently, was only theoretical. The work was described in the September 25 Journal of Nature.

The discovery, according to Lukin, contrary to popular belief about the nature of light, established over decades. Photons long described as massless particles that do not interact with each other. Point the two laser beams at each other, and they just pass through.

“Photonic molecule” do not behave like a traditional lasers and more and more as what was thought to be impossible and foolish child of science fiction – the lightsaber.

“Most of the properties of light as we know, comes from the fact that photons have no mass and do not interact with each other,” – said Lukin. – “We have created a special type of environment in which the photons are so strongly interact with each other, they begin to act as if they have mass, and bonded together to form molecules. This type associated photon state was discussed for a long time, but has remained a theory. We can compare it with the behavior of light swords. When such photons interact with each other, they are crushed and reject each other. Physics of what is happening in these molecules is similar to what we see in the movies. ”

To get the usual massless photons communicate with each other, Lukin and his colleagues could not count on something like the Force, but just took a set of more extreme conditions.

The researchers began with the pumping of rubidium atoms in a vacuum chamber, followed by a cloud of laser cooled atoms to a few degrees above absolute zero . Using extremely weak laser pulses, then they vystrelivali single photons in a cloud of atoms.

When a photon hits a cloud of cold atoms, said Lukin, their energy excites the atoms in the way, resulting in extremely slow down photons. While a photon moving through the cloud, the energy transferred from one atom to another in and out of the clouds with the photon.

“When a photon comes from the environment, its identity preserved” – says Lukin. – “About the same effect we see during the refraction of light in a glass of water. The light enters the water, gives the energy environment, and in it there is a relationship of light and matter. But when it comes remains light. In our case, the process is exactly the same, but more extreme: the light is slowed down considerably and is much more energy is given, than during the index. ”

When Lukin and colleagues have launched two photons in the cloud, they were surprised to find that there was a whole molecule of the two photons.

Why do they have merged into a hitherto unseen molecule?

Молекулы света

Photons with a strong mutual attraction in quantum nonlinear medium. Image: Nature

The effect of the blockade of the Rydberg – says Lukin. This is when an atom is excited, the nearest atoms can not be brought up to the same extent. In practice, this effect means that when the two photons are included in the atomic cloud, the first atom is excited, but have to move forward before the second photon excites the atoms coming. As a result of two photons pull and push each other through the cloud, their energy is transferred from one atom to another.

“This is a photon interaction around the interaction of atoms” – says Lukin. – “The two photons behave like a molecule, and when they come out of the environment, they are likely to do so than as a single photon.”

Although the effect is quite unusual, it has several practical applications.

“We do it for fun and because we need to expand the boundaries of science,” – says Lukin. – “But it feeds the bigger picture, since the photons are the best way to transfer quantum information. The problem was that the photons do not interact with each other. ”

To build a quantum computer, researchers need to create a system that can store quantum information and use it in the process of quantum logic operations. But quantum logic requires the interaction between individual photons.

“Our experiment showed that such a process is possible. Before you make a useful and practical quantum photonic switch or logic board, we need to improve performance, so still in the development stage, but it is an important step. Important physical principles established by us. ”

The system can be used even in the classic computer calculations, given the problems with the scattering of energy faced by chip makers. A number of companies, including IBM, have developed their own systems, which rely on optical routers that convert light into electrical signals, but these systems have their own problems.

Lukin also suggested that one day the system could be used to create complex three-dimensional structures – for example, the crystals – completely out of the light. What time of the crystals already in the making.

“How is it useful to us, do not know yet. But this new state of matter, so we can hope that he can find application as the study of the properties of photonic molecules. ”
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