Light moves really, really fast. In fact, Einstein showed that nothing can travel faster than the speed of light in a vacuum. Even in air, light travels approximately 300 million metres every second. To give you a sense of scale, it only takes light about 1.3 seconds to travel between the earth and the moon! For years, scientists have been trying to find ways to slow light down and bring it to a full stop. Now, researchers at the University of Darmstadt in Germany have been able to actually stop light for a full minute before they let it move again.
To stop light, the scientists used the principles of quantum physics (the rules of quantum physics governs the behaviour of really small things like atoms and elementary particles) to manipulate the properties of the atoms in a custom-made crystal. The crystal was cooled down to cryogenic (really, really cold) temperatures. In its normal state, the crystal is opaque—it doesn’t let light pass through it. However, the researchers were able to manipulate the atomic properties of the crystal so that it became transparent to a certain frequency of light. In other words, they built an “on/off switch” that allows light to pass through the crystal. Initially, this “switch” was turned on and a laser was shone through the crystal. Then the “switch” was turned off so that the crystal became opaque again. At this point, the light that was moving inside the crystal actually stopped!
What happened to the light?
When the crystal became opaque, the light energy was transferred to the atoms in the crystal. The properties of the atoms that “absorbed” this light were changed at the quantum level. When the crystal became transparent again, this energy was converted back into laser light that exited the crystal. The atoms in the crystal stopped the light, “stored” it and then released it at a later time! The problem is that while the spooky rules of quantum physics allow the atoms to stop and “store” the light, it is technically very difficult to keep the light energy “stored” for any length of time. This is why stopping the light for a single minute is such an achievement.
There are many practical uses for being able to stop and store light signals. In fact, the outcome of this experiment is crucial to the future of computing and communications. Information (internet/telephone data) can be delivered around the world very quickly as light signals passing through fibre optic cables. The ability to control the traffic of these light signals by starting/stopping/directing them as they move around the world will allow us create super-fast and super-secure telecommunication networks.
If you are interested in exploring the science behind light, then on your next visit to TELUS World of Science check out the Fibre Optic and Infrared Camera exhibits located in the Eureka! Gallery on the second floor.
The original research paper “Stopped Light and Image Storage by Electromagnetically Induced Transparency up to the Regime of One Minute” by Georg Heinze, Christian Hubrich and Thomas Halfmann is available (for a fee) in the current edition of Physical Review Letters.
To further explore light and lasers, check out our interactive, online game about lasers.