Are real lightsabers around the corner?
Researchers from Harvard University and MIT have showed that photons may interact with one another in certain conditions, forming a two-photon bound state, which is a single molecule made of two photons.
With this discovery, the development of optical computers may be easier and more feasible – and the photon’s behavior is similar to that we see in science fiction’s lightsabers.
Science Fiction Becoming Reality?
The photons’ behavior observed in this study has been likened to that of lightsabers, the fictional weapons favored by the Jedi Knights in the Star Wars movies.
The lightsaber behaves as a “solid” beam of light of a finite length, as opposed to a laser beam which will continue until it hits something.
The photons interacting in this experiment behave similarly to molecules, pushing against and sticking to each other, and could conceivably be manipulated to create a solid “blade” of light.
May the Force be with us indeed!
What Are Photons?
Photons are the basic particles which constitute an electromagnetic radiation (light). Each photon has an energy which depends on the value of its wavelength. Photons can travel through either a vacuum or through other media (i.e. air, water or solid materials); their speed is affected by the characteristics of the medium they travel through.
Scientists have studied photon behavior in recent years for photons’ potential in computing; some people believe that photon-based computers, or optical computers, instead of the electron-based computers currently used, are the machines of the future.
Even more excitingly, photon-based computers could operate in the quantum regime, thus forming a quantum computer.
All theories studying the behavior or photons and their technological applications were based on a fundamental assumption, which is that photons do not interact with each other; this means that no forces such as attraction or repulsion occur between different photons. From this point of view, therefore, photons behave differently from other conventional particles (i.e. electrons).
Physicists, however, have considered with great interest the possibility of such interactions, as these could lead to new technological applications, including those for optical and quantum computers.
Photon Attract: Physics Breakthrough
Researchers from the Institute of Physics of Harvard University (US) reported groundbreaking results in this field; the study they performed was done in cooperation with the Massachusetts Institute of Technology (MIT, US) and the Californian Institute of Technology (US). The results were published on Nature on the 25th of September 2013.
In their experiments, they show that, in particular conditions, photons can show attractive forces between each other.
Photon Interactions: The Experiment
Dr. Thibault Peyronel, from Harvard University, one of the scientists involved in the study, explained the work to Decoded Science.
“In the past, there have been several theoretical studies to understand which were the ideal conditions for photons to interact; what we did was to base our experiments on these models.
We created a new medium, in which the interactions of the photons could take place. To do this, we used a vapor of rubidium (Rb) atoms in a vacuum chamber, laser- cooled at a very cold temperature (40 microKelvins above absolute zero). In these conditions, Rb atoms are diluted and motion-less. Then we shined small number of photons onto the vapor and observed in which state(s) the photons were exiting the chamber.”
Two-Photon State: The Results
According to Dr. Peyronel “we could see that a strong interaction between two photons took place; they combined together into a two-photon state, something similar to a molecule made of two photons. It was the first time something like this was actually observed. It has to be highlighted that we achieved these results in a single-pass; indeed we did not use an optical cavity to give photons many chances to interact. This makes the results even more important.”
Future Technological Applications
Talking about technological application (not related to science fiction), Dr. Peyronel said: “I think these photons´ interactions can be the basis for building photonic quantum computers. Clearly there is still a lot of work to be done, but for the first time we proved that it is possible to have such interactions without resorting to complex cavity-based experiments.”
Fistenberg, O. et al. Attractive photons in a quantum nonlinear medium. (2013). Nature, doi:10.1038/nature12512. Accessed September 30, 2013.
Peyronel, T. et al. Quantum nonlinear optics with single photons enabled by strongly interacting atoms. (2012). Nature, 488, 57-60. Accessed September 30, 2013.
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