Nav: Home

A one-way street for light

November 14, 2019

Light can be directed in different directions, usually also back the same way. Physicists from the University of Bonn and the University of Cologne have however succeeded in creating a new one-way street for light. They cool photons down to a Bose-Einstein condensate, which causes the light to collect in optical "valleys" from which it can no longer return. The findings from basic research could also be of interest for the quantum communication of the future. The renowned journal "Science" now presents the results.

A light beam is usually divided by being directed onto a partially reflecting mirror: Part of the light is then reflected back to create the mirror image. The rest passes through the mirror. "However, this process can be turned around if the experimental set-up is reversed," says Prof. Dr. Martin Weitz from the Institute of Applied Physics at the University of Bonn. If the reflected light and the part of the light passing through the mirror are sent in the opposite direction, the original light beam can be reconstructed.

The physicist investigates exotic optical quantum states of light. Together with his team and Prof. Dr. Achim Rosch from the Institute for Theoretical Physics at the University of Cologne, Weitz was looking for a new method to generate optical one-way streets by cooling the light particles (photons): As a result of the smaller energy of the photons, the light should collect in various valleys and thereby be irreversibly divided. The physicists used a Bose-Einstein condensate made of photons for this purpose, with which Weitz made a name for himself in 2010 because he was the first to create such a "super-photon".

A beam of light is thrown back and forth between two mirrors. During this process, the photons collide with dye molecules located between the reflecting surfaces. The dye molecules "swallow" the photons and then spit them out again. "The photons acquire the temperature of the dye solution," says Weitz. "In the course of this, they cool down to room temperature without getting lost."

By irradiating the dye solution with a laser, the physicists increase the number of photons between the mirrors. The strong concentration of the light particles combined with simultaneous cooling causes the individual photons to fuse to form a "super photon", also known as Bose-Einstein condensate.

Two optical valleys "catch" the light

The current experiment by the team of physicists from Bonn and Cologne worked in accordance with this principle. However, one of the two mirrors was not completely flat, but had two small optical valleys. When the light beam enters one of the indents, the distance, and therefore the wavelength, becomes slightly longer. The photons then have a lower energy. These light particles are "cooled" by the dye molecules and then pass into a low-energy state in the valleys.

However, the photons in the indents do not behave like marbles rolling over a corrugated sheet. Marbles roll into the valleys of the corrugated sheet and remain there, separated by the "peaks". "In our experiment, the two valleys are so close together that a tunnel coupling occurs," reports lead author Christian Kurtscheid from the Weitz team. It is therefore no longer possible to determine which photons are in which valley. "The photons are held in the two valleys and enter the lowest energy state of the system," explains Weitz. "This irreversibly splits the light as if it were passing through an intersection at the end of a one-way street, while the light waves remain in lockstep in different indents."

The scientists hope that this experimental arrangement will make it possible to produce even more complex quantum states that allow the generation of interlaced photonic multi-particle states. "Perhaps quantum computers might one day use this method to communicate with each other and form a kind of quantum Internet," says Weitz with a view towards the future.
-end-
Publication: Christian Kurtscheid, David Dung, Erik Busley, Frank Vewinger, Achim Rosch, and Martin Weitz: Thermally Condensing Photons into a Coherently Split State of Light, Science, DOI: 10.1126/science.aay1334

Media contact:

Prof. Dr. Martin Weitz
Institute of Applied Physics
University of Bonn
Tel: +49-(0)228-73-4837 or 73-4836
E-mail: Martin.Weitz@uni-bonn.de

Christian Kurtscheid
Institute of Applied Physics
University of Bonn
Tel. +49-(0)-228-73-60458 or 73-3455
E-mail: kurtscheid@iap.uni-bonn.de

University of Bonn

Related Photons Articles:

Photons and electrons one on one
The dynamics of electrons changes ever so slightly on each interaction with a photon.
An advance in molecular moviemaking shows how molecules respond to two photons of light
Some of the molecules' responses were surprising and others had been seen before with other techniques, but never in such detail or so directly, without relying on advance knowledge of what they should look like.
The imitation game: Scientists describe and emulate new quantum state of entangled photons
A research team from ITMO University, MIPT and Politecnico di Torino, has predicted a novel type of topological quantum state of two photons.
What if we could teach photons to behave like electrons?
The researchers tricked photons - which are intrinsically non-magnetic - into behaving like charged electrons.
Producing single photons from a stream of single electrons
Researchers at the University of Cambridge have developed a novel technique for generating single photons, by moving single electrons in a specially designed light-emitting diode (LED).
Counting photons is now routine enough to need standards
NIST has taken a step toward enabling universal standards for single-photon detectors (SPDs), which are becoming increasingly important in science and industry.
Scientists have found out why photons flying from other galaxies do not reach the Earth
In the Universe there are extragalactic objects such as blazars, which very intensively generate a powerful gamma-ray flux, part of photons from this stream reaches the Earth, as they say, directly, and part -- are converted along the way into electrons, then again converted into photons and only then get to us.
Researchers discover new way to split and sum photons with silicon
A team of researchers at The University of Texas at Austin and the University of California, Riverside have found a way to produce a long-hypothesized phenomenon -- the transfer of energy between silicon and organic, carbon-based molecules -- in a breakthrough that has implications for information storage in quantum computing, solar energy conversion and medical imaging.
Breaking the limits: Discovery of the highest-energy photons from a gamma-ray burst
Gamma-ray bursts (GRBs) are brief and extremely powerful cosmic explosions, suddenly appearing in the sky, about once per day.
Massive photons in an artificial magnetic field
An international research collaboration from Poland, the UK and Russia has created a two-dimensional system -- a thin optical cavity filled with liquid crystal -- in which they trapped photons.
More Photons News and Photons Current Events

Trending Science News

Current Coronavirus (COVID-19) News

Top Science Podcasts

We have hand picked the top science podcasts of 2020.
Now Playing: TED Radio Hour

Teaching For Better Humans 2.0
More than test scores or good grades–what do kids need for the future? This hour, TED speakers explore how to help children grow into better humans, both during and after this time of crisis. Guests include educators Richard Culatta and Liz Kleinrock, psychologist Thomas Curran, and writer Jacqueline Woodson.
Now Playing: Science for the People

#556 The Power of Friendship
It's 2020 and times are tough. Maybe some of us are learning about social distancing the hard way. Maybe we just are all a little anxious. No matter what, we could probably use a friend. But what is a friend, exactly? And why do we need them so much? This week host Bethany Brookshire speaks with Lydia Denworth, author of the new book "Friendship: The Evolution, Biology, and Extraordinary Power of Life's Fundamental Bond". This episode is hosted by Bethany Brookshire, science writer from Science News.
Now Playing: Radiolab

Space
One of the most consistent questions we get at the show is from parents who want to know which episodes are kid-friendly and which aren't. So today, we're releasing a separate feed, Radiolab for Kids. To kick it off, we're rerunning an all-time favorite episode: Space. In the 60's, space exploration was an American obsession. This hour, we chart the path from romance to increasing cynicism. We begin with Ann Druyan, widow of Carl Sagan, with a story about the Voyager expedition, true love, and a golden record that travels through space. And astrophysicist Neil de Grasse Tyson explains the Coepernican Principle, and just how insignificant we are. Support Radiolab today at Radiolab.org/donate.