Sina science and technology news on March 16, Beijing time, according to foreign media reports, in many ways, scientists are like detectives, searching for clues in the evidence and solving one mystery after another. For example, whether it is edible salt or crystal, all crystals are composed of a pile of repeatedly arranged atoms. Just look at a few atoms that can reflect the law, and you can roughly infer how other atoms are arranged.
But what if such a law is not reflected in space, but in time? What if the relationship between the various components is not “up, down, left and right”, but “successively”? This counter intuitive concept is the basis of time crystal, that is, a quantum system that can exhibit crystal like predictable repetitive behavior. In 2012, MIT physicist and Nobel laureate Frank welchek predicted the existence of time crystals for the first time in theory. After years of hard research, experimentalists did not finally create a time crystal until 2021. However, a team of physicists recently made another major progress: using light to make time crystals. The research report was published in the journal Nature communication in February this year. This research will transform the time crystal from an ethereal wonder into a real device component.
Although the behavior of the time crystal will be repeated in time, it is not as simple as a clock. Clocks and watches need external energy to operate, but for time crystals, ticking like clocks and watches is precisely its most natural and stable state. This is just opposite to the thermodynamic equilibrium understood by physicists, that is, once energy enters a system, it will inevitably dissipate in the end, just like a pot of hot water boiled and placed at room temperature. The time crystal is like a pot of water that is always boiling and will never cool down. From some definitions, time crystal represents a unique new state of matter. The most remarkable feature is that it violates the law of thermodynamic equilibrium and the state remains unchanged. This material is like its own metronome, so it may be used for precise timing or quantum information processing in the future.
Time crystal has stepped out of the stage of pure theoretical concept, and people have begun to explore its technical application. However, researchers still have a long and arduous way to go if they want to get more time out of the laboratory and put it into practical application. To find out whether an experiment produces a time crystal, it usually requires either extremely complex and daunting experimental devices or a powerful quantum computer.
The research team used a relatively simple method to drive two laser beams into a disk-shaped crystal cavity with a diameter of 1mm. The two lasers bounce back and forth in the cavity and collide constantly. The researchers deliberately selected the shape of the cavity and controlled the characteristics of the laser beam, so that the light reflected by the laser has a law that no ordinary light has ever formed: the laser reflected back and forth in the cavity forms multiple solitary waves. These waves have predictable periodicity and perfectly matched rhythm, so they can be regarded as a time crystal.
If you stand at the exit of the cavity with a light detector in a mini version, the light intensity you detect will initially change periodically, depending on the characteristics of the laser beam. But at some point, the pattern of light intensity you detect will suddenly change. Just like when watching a movie on TV, the movie suddenly starts fast forward, and the speed of fast forward seems to be determined by some invisible mechanism in the display, which is completely out of your control. We can also see some periodic characteristics in these light waves, but these periods are actually twice, three times or other integer times of the laser’s own period. The growth of the cycle indicates the emergence of a quantum system that can naturally time itself – in other words, a light-based time crystal.
N it’s like hanging a thread in salt water to cultivate salt crystals. Adjusting the laser characteristics is like adjusting the structure of the wire you put in salt water. Whether it is laser or line, its function is only to help the formation of crystal, but the periodicity and repetition law of crystal are completely determined by itself.
Previous research used a variety of “basic components” to create time crystals. This experiment proves that using laser to manufacture time crystal has more practical advantages. Most importantly, the time crystal created by the team can work normally in a relatively ordinary environment. Most quantum materials must be in extreme conditions such as ultra-low temperature to reflect quantum properties. Once they leave the laboratory, they will become ordinary. This experiment is very important because it is carried out at a relatively high temperature, which is closer to the various complex processes we observe in our daily life.
The time crystal developed this time is very “tough” in the real world. The system will also lose energy randomly and gradually produce noise (just like the TV overheats and snowflakes appear on the screen when watching a movie), but it also enhances the stability of the system. Generally speaking, these two problems will try to destroy the crystallinity of the system. In order to avoid such external disturbances, the time crystal must be strictly isolated from the environment, but the new system has found a balance in it.
Due to the mutual containment of energy passing and noise through “conspiracy”, the time crystal developed this time is likely to be put into practical application in the future. Some basic components are also used to manufacture this time crystal, but the number is small. The device architecture used is still relatively simple, which should not be a problem for many research teams. It is hoped that this simple and durable design will play a key role in future research, whether for basic physics research and practical applications, such as accurate timing.
As a timing device, the accuracy of the laser based time crystal may be slightly inferior to that of the most popular atomic clock. However, its stability and simplicity are very suitable for communication or computing devices, because these devices not only need accurate timing, but also can not be too fragile. They also need to operate normally in ordinary environments outside the laboratory. In addition, some common electronic component production technologies may also integrate the time crystal into the chip, making the system easier to adapt to existing consumer products.
Physicists can study large-scale time crystals by studying traditional space crystals for decades, and judge whether time crystals will behave unexpectedly when they have specific defects or are exposed to excessive energy. These behaviors are generally difficult to detect in small crystals, and the laser system can reach a large scale, which opens a new door to this research field. This is a new kind of physical state, or a virgin land, a new world waiting for us to discover. (leaves)