Light illuminates the world in a rainbow of colors. There would be no color nor light in the world without photons, the tiny particles in packets of energy to create light.
In research that has implications for the speed of communication, physicists at the University have made history by breaking the color barrier for sending and receiving these photons, also known as quanta.
The University’s Knight Professor of Liberal Arts and Sciences Michael Raymer and doctoral student Hayden McGuinness worked together to experiment and devise a method to change the color of single photons, or particles of light, in a fiber optic cable. Before, it was only possible to change the color of multiple photons at one time.
Because fiber optic cables are used in telecommunications for technology including the Internet, telephones and cable television, their research has implications for the future of communication. Being able to change the color of a single photon could lead to much faster transmission of photons and, therefore, communication signals.
For their research, the scientists sent high-powered pulses of laser light of a certain color, or wavelength, through a custom-made optical fiber to produce single photons with different colors.
The researchers used a dual-color burst of laser light in a separate custom-made optical fiber to change the color of one of the photons. This is called Bragg scattering, which occurs when a tiny amount of energy is transmitted between a laser light and a single photon. This exchange, also known as quantum frequency translation, causes the photon to change colors. This process allows a device that uses a specific color to communicate with a device that uses a different color while still maintaining all of the device’s quantum properties.
“Each e-mail that you receive was transmitted by sending probably millions of short laser pulses, each pulse containing about 1,000 laser pulses,” Raymer said.
Raymer teaches a class about the physics of the Internet and also authored the textbook “The Silicon Web: The Physics for the Internet Age.”
McGuinness elaborated further upon the way photons work in communication.
“Information is sent in a pattern of pulses, similar to Morse code,” McGuinness said.
McGuinness was the primary scientist performing the experiment. He set up the optical fibers and built one of the lasers for the single-photon experiment, while the other laser was store-bought.
The research was stimulated by previous work done by Raymer with his collaborators at Alcatel-Lucent Bell Labs and the University of California, San Diego, according to a Sept. 30 University press release.
The experiment has allowed the technology of a quantum network to be realized, in which single photons and electrons could carry signals.
Instead of using thousands of photons to store information, quantum computers could use individual photons to store information, McGuinness and Raymer said.
“The way it works is that each bit of information is carried on one photon. That’s the main difference, as opposed to a thousand photons in the current system,” Raymer said.
Quantum computations have been carried out in labs around the world, but quantum computers do not yet physically exist.
“They can do much larger calculations faster,” University physics and astronomy professor James Schombert said.
Quantum computers could be used for simulation, solving complex problems, robotics specialists creating artificial intelligence, and people who are on the cutting edge of cryptography, he said.
“We’ve already provided now the translation capability that would allow (quantum computers) to communicate,” Raymer said.
Quantum computing could also make computer hackers obsolete by more efficiently securing data.
“For quantum cryptography, basically, by using the laws of quantum physics, you can make it so that it’s impossible for someone who is not the transmitter or the receiver to effectively intercept the code,” McGuinness said.
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