Physics

Photons entangled to make new form of light

Photons entangled to make new ...
An MIT and Harvard team have developed a way to make photons of light interact with each other, which could have applications in quantum computing
An MIT and Harvard team have developed a way to make photons of light interact with each other, which could have applications in quantum computing
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An MIT and Harvard team have developed a way to make photons of light interact with each other, which could have applications in quantum computing
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An MIT and Harvard team have developed a way to make photons of light interact with each other, which could have applications in quantum computing

Photons, the elementary particles that make up light, are known to be fast, weightless and to not interact with each other. But in new experiments, physicists at MIT and Harvard have now created a new form of light, demonstrating that groups of photons can be made to interact with each other, slow down and gain mass.

The new study builds on the team's earlier research into making "photonic molecules," which involved coaxing pairs of photons into interacting with each other. If that kind of unexpected interaction could take place between two photons, the team reasoned, could it happen between three or more?

"For example, you can combine oxygen molecules to form O2 and O3 (ozone), but not O4, and for some molecules you can't form even a three-particle molecule," says Vladan Vuletic, lead researcher on the study. "So it was an open question: Can you add more photons to a molecule to make bigger and bigger things?"

To find out, the team ran similar experiments to those earlier ones. First, they ultracooled a cloud of rubidium atoms down to almost absolute zero, which effectively freezes them in place. Then, they shone a very weak laser beam through this cloud of stationary atoms. This beam only sends a few photons through at a time, and the scientists then measured them when they emerged from the cloud.

Normally, a stream of single photons would exit the cloud at random intervals, but in this case, they were seen to emerge in groups of two and three. Not only were the photons exhibiting attraction, but they'd actually gained mass – only that of a fraction of an electron, but that's a leap for a normally weightless particle. Gaining mass also slowed down their speed, making them about 100,000 times slower than the speed of light they'd normally travel at.

The researchers also measured the frequency of the photons' oscillation, known as their phase. The larger the phase, the more strongly particles are interacting, and the team found that three-photon molecules had a phase shift three times larger than that of photon pairs.

"What was interesting was that these triplets formed at all," says Vuletic. "It was also not known whether they would be equally, less, or more strongly bound compared with photon pairs."

So why are the normally lone-ranging photons suddenly interacting with each other? The team's hypothesis is that as photons bump into the rubidium atoms, they form polaritons – quantum particles that are part-light and part-matter. Polaritons have mass, which is how they can bind to other polaritons. Once they leave the cloud, the atoms they've picked up stay behind, but the photons remain bound together.

Since these bound photons are essentially "entangled", they could find use in quantum computing.

"Photons can travel very fast over long distances, and people have been using light to transmit information, such as in optical fibers," says Vuletic. "If photons can influence one another, then if you can entangle these photons, and we've done that, you can use them to distribute quantum information in an interesting and useful way."

Attraction is just one way that photons may be able to interact, and in future the researchers plan to experiment with other kinds of interactions, including making photons repel each other.

"It's completely novel in the sense that we don't even know sometimes qualitatively what to expect," says Vuletic. "With repulsion of photons, can they be such that they form a regular pattern, like a crystal of light? Or will something else happen? It's very uncharted territory."

The research was published in the journal Science.

Source: MIT

14 comments
wolfhammer
Lets think outside the box, "Gaining mass also slowed down their speed, making them about 100,000 times slower than the speed of light they'd normally travel at." What if the experiment slowed down the photon's, and that slower speed allowed them to pick up mass?
MarkmBha
Amazing.
ColinChambers
photons cannot gather mass. electrons focus Anglia information energy’s , into photons travel by quantum links ,as a positive push Energy motion . Photons engage instantly into a black spectrum negativity Energy , which adds a pull value ..... interaction between two opposing photons using the same quantum link . Will lose by stages negativity [pull]. positivity [push] = loss in light speed . Elementary particles are not photons.? try looking at ,Copenhagen interpretation . by deflection of negative angular waves from its detector , detected at slits . Jacktar
flylowguy
Light and I have a purely photonic relationship.
notarichman
if the speed of these entangled photons is speed of light/100,000 = about 3000 m/s; and the speed of electricity through a copper wire is almost the speed of light; then how would using entangled photons increase the speed of a computer?
Wolf0579
I'm glad the scientists doing the work probably do not read the comments in this rag... it's good that they don't need an audience that understands what they're doing.
Username
We already knew that light (therefore photons) interacts with itself (without intermingling) from this experiement https://www.technologyreview.com/s/414412/light-repels-light/ Which should make us question whether light bends around stars because space is warped or simply because it's attracted to the giant light source. Light is part of the electromagnetic spectrum but somehow in it's specific frequency range there's an abnormal (not found elsewhere) particle. Part of the confusion surrounding light is probably simply due that we can detect it with our eyes and naturally categorize it as distinct. My point is that we are far from understanding exactly what light is.
Expanded Viewpoint
If photons have no weight to them, then how do radiometers work? You know, those glass globes with the white and black painted squares that spin when light hits them? Light of any given frequency (color of the spectrum) acts as both a wave of energy (through a diffraction grating) and as a particle (makes a radiometer spin). Also, all of the gaseous elements except for the noble gasses, always naturally run around in pairs, sharing their outer shell electrons in order to be stable instead of reacting with another element spontaneously. But eventually, Oxygen will cause steel to rust and Carbon to form CO2 and other reactions will occur between other elements also. Ozone (O3) is a form of Oxygen molecule that breaks back down again into O2 and becomes more stable again. So two molecules of O3 will recombine into three molecules of O2. It takes high amounts of energy to convert O2 into O3, and when that energy is dissipated, you get a reversion of the Oxygen back to its ground state. Randy
CharlieSeattle
So, make a Light Sabre work now and impress us!
Nikola Milovic
These scientists alter and impose photons of orders on how to behave, all of which work with lasers, which are some kind of photon beam, but forced to behave. How, then, believe that "photon under pressure" - (laser). can order a photon how to behave, and what is nonsense, that photons turn into mass.