They really caught the light and stored it! A great change may be coming
As we all know, light propagates very fast and can propagate at a speed of about 300,000km/second. Looking at the entire earth, it is almost impossible to find anything faster than the speed of light.
Because of this, people are full of illusions about the speed of light. Some people think that exceeding the speed of light can go back to the past, and some people think that exceeding the speed of light can travel through parallel universes. Even some particle experiments will make a few particles move at the fastest speed. Impact.
If you want to further observe the secret of "light", you need extremely fast speed, either keeping a similar speed to it, or exceeding the speed of light. This is the direction that scientists are constantly working towards. After long-term research by experts in the field of optical storage in my country, The matter of struggle and "catching the light" finally took shape.
Light, as a kind of transmitting heat and energy, has extremely fast speed. Scientists grasp this point and hope to capture and store light, so as to use the speed of light to transmit various human information. So in their After careful deployment, fiber appeared.
- Optical fiber
We often hear the word "optical fiber", but few people understand the secret of optical fiber. As a fiber made of glass or plastic, it is also called an optical fiber and can be used as a light conductor. tool. The working principle of
optical fiber is very simple. The end point utilizes the total reflection property of light. When the angle of the light hitting the interface between the inner core and the outer layer is greater than the critical angle of total reflection, the light cannot pass through the interface and will instead be reflected inside the fiber. Reflected everywhere.
In short, the optical fiber uses two sets of glass with different refractive index, and uses the angle between the glass and the light to achieve the effect of " total reflection ".
This is actually the process of "capturing" and "storing" light, but during this process, the light will still run at extremely fast speeds instead of being passively "stored" inside the optical fiber. So, what should we do? How can we truly "store" it?
- Storage of light
First of all, we must understand one thing. Light is difficult to capture and store. If we want to store light, we must ensure that its properties will not change drastically.
To give a simple example, we all know that tiny particles such as "electrons" will increase or decrease with changes in energy during movement. Using this principle, scientists and engineers built integrated circuits and successfully controlled The direction of movement of electrical energy has since given birth to signals of 0 and 1. The signal
is used extensively by us humans as a communication signal. Our network is built based on motion signals such as electrons.
However, light quanta and electrons are completely different. To capture and utilize light quanta , in addition to considering the difference in their energy size, we must also consider the change interval of the light quanta. Once the phase change of the light quanta exceeds the artificially set interval, We will not be able to read the information stored in it.
Therefore, in the process of storing light, we must strictly control this changing range and try to keep the light quanta within our controllable range. From this perspective, storing light quanta is much more difficult than storing electrons. .
- Principle of optical storage
As early as the 1980s and 1990s, the theory of optics had already emerged. After long-term development and exploration, scientists proposed the theory of "Electromagnetically Induced Transparency".
This theory can be simply understood as: a tiny medium absorbs a beam of light of a certain frequency first. When the second beam of light shines on this tiny medium, it will try its best to absorb the second beam of light, but give up on the first beam. Absorption of frequency light, this theory lays the foundation for the storage method of light.
According to this theory, if we want to realize the storage of light, we must meet two conditions: First, we need two beams of frequency and phase-locked light sources, one of which is a stronger controllable light source, and the other is a weaker beam. signal light source; secondly, the two beams of light interact with the three-level atomic medium, which can cause the two beams of photons to resonate simultaneously.
As long as these two points can be achieved, scientists can control the light source and manipulate the speed of light to gradually slow down the speed of light.
On the premise that the speed of light is slowing down, scientists have created a theoretical model - the dark state polarization model. During the deduction of this model, the slowed down speed of light can tend to "stagnate" or even be infinitely close to 0 .
If this speed can really be achieved, then the speed of us humans will exceed the slowed down "speed of light". In this state, we can easily store light.
Although the theory of storing light has been established, and the deduction of the model has proved the relevant results, our current scientific level still has a long way to go, and a large number of engineering problems have yet to be solved.
- Light storage medium
Storing light is not a simple matter. To truly store light, we must choose suitable materials.
In 2001, Hau, a physics experiment group at Harvard University, used nanocold atoms as the medium to realize the reading and writing of optical pulse signals, but the optical storage time was only 1 millisecond.
In 2003, based on this, the Lukin group of Harvard University achieved 800 milliseconds of optical storage and release after long-term improvements and experiments. However, these few hundred milliseconds were too short to prove the success of the experiment.
In 2005, Australian scientists used the medium of praseodymium-doped yttrium silicate crystal solid material to achieve 1 second of light storage. Researchers at the University of Darmstadt in Germany improved on this basis and finally achieved it in 2013. Achieved 1 minute of optical information storage.
There are corresponding examples in my country. In 2015, the experimental teams of Professor Li Chuanfeng and Zhou Zongquan of the University of Science and Technology of China discovered the special structure of rare earth ions. This structure is very rare and can be well used in optical storage. fields and quantum storage fields.
So they selected from 17 rare earth metals and decided to use europium element metal as the doping ion in the crystal. Under their strict control, they created an hour of light storage time.
According to the estimation of Professor Li Chuanfeng, as the experiment continues to improve, the storage time will also increase, and theoretically it can be stored for about a month.
Under the long-term experiments of Chinese scientists, the total duration of optical storage reached 1 hour, and the storage fidelity also reached the level of 96.4±2.5%, which laid the corresponding foundation for the construction of large-scale quantum networks.
The significance of storing light
Many people are full of doubts about optical storage and think it is a meaningless thing, but in fact, optical storage plays a very big role in quantum communication , and optical fiber propagation is often accompanied by Due to exponential molecular consumption, the optical fiber propagation distance is often limited to a certain range.
But by storing light, we can build quantum repeaters to overcome the loss of optical fiber propagation. If we equip quantum relay satellites with optical storage technology, we can create a global coverage within an hour. quantum information, and then build a long-distance quantum communication network.
Conclusion
"Light" is a part of our daily life, and it is also an endless rich treasure of nature. With the development of science and technology, we will use more and more light energy, and related basic research will also become more and more important. The more perfect it is, the successful storage of light by humans is a node in the development of science and technology, and it is also a new beginning for science and technology to progress again.
