I Just Want to Be a Quiet Top Student

In fact, as early as the beginning of the 20th century, physicists noticed that light has a radiation pressure effect on atoms. Due to the limitations of instruments and equipment, it was not until the invention of laser cooling devices in recent decades that the laser cooling technology of atoms was substantially realized. develop.

In Stanford's laboratory, Mr. Steven Chu used a three-dimensional laser beam to form a magneto-optical trap to trap atoms in a small area for cooling, and obtained a lower temperature optical glue. This was in 1985.

After more than ten years of painstaking research, Mr. Zhu and his scientific research partners went to the next level. They used this technology to obtain extremely low temperatures below the limit of photon recoil. With this achievement, Mr. Zhu, Cohen-Darocki, and Phillips won the Nobel Prize in Physics at the same time in 1997.

After more than ten or twenty years and entering the 21st century, in the laboratory of Nangang No. 2 Middle School, Mr. Mu proposed a question based on the research results of the Nobel Prize in Physics: "In the laser cooling experiment of atoms, considering the recoil effect , what is the minimum value of temperature?

All the students in the audience scratched their heads and scratched their heads: "Mr. Mu, we are only high school students. With this brain hole, we won't win the Nobel Prize?"

Only Shen Qi remained silent, he understood the meaning of Teacher Mu's question, she didn't expect any high school student to have the level of Nobel Prize.

This question is about laser emitters and atomic confinement. At first glance, it looks very high-end. In the final analysis, the laser cooling experiment of atoms is a verification of the theoretical assumptions of Doppler, de Broglie and others, and it has been carried forward and gradually improved.

In high school physics textbooks, high school students learn the Doppler effect, de Broglie waves, the wave-particle duality of light, the Bohr energy level model, alpha particle bombardment, and the basic theory of atoms and electrons. Of course, these are the most difficult parts of high school physics to understand.

Shen Qi has already learned big things by himself, and the obstacles for him to understand are relatively small.

As far as solving problems is concerned, if you cannot master the necessary mathematical tools (formulas, inferences, theorems, etc.), you will be helpless and unable to solve the corresponding mathematical problems, and physics problems are more about the progression of understanding. Count in small amounts.

"This doesn't require Nobel Prize-level brains, you just need to have physics competition-level brains." Teacher Mu smiled and asked, "Do you think this problem is difficult?"

"Disaster!"

"The IPhO's medium-difficulty test questions, or the CPhO national final theory test questions, are about the same difficulty." Teacher Mu glanced at the stage for the next week and said, "You must know that when you participate in the competition, no one will show you a teaching video. You can watch it." Less than the 3D demonstration animation, the only clue is the plan view on the scroll. Here, it is similar to the plan view on the screen. So I will play the animation for you, play it twice, and explain it to you simultaneously, you should not show it The ignorant expression of a curious baby. Future physicists, show some real skills, please don't let me down."

The audience was instantly silent.

Naturally, the level of the members of the Wujing team is not too bad, and Shen Qi is not the only one who has self-taught electives or some knowledge about big things.

All the members of the Wujing team picked up their pens and immersed themselves in writing and drawing on the draft pad, deriving calculations.

Shen Qi did not bring a pen or paper, he came empty-handed, staring at the two-dimensional diagram of the atomic reference system on the screen, concentrating on something.

"Brother, it's impossible for you to calculate the minimum temperature in your head, right?" Lin Xingyu wrote and found that Shen Qi beside him was sitting firmly with his arms crossed.

"Mental arithmetic? It doesn't exist." Shen Qi shook his head and spread his palm: "Here comes the pen."

Lin Xingyu had a bunch of pens in his pen bag, and he took out one of the most expensive water-based pens and handed it to Shen Qi.

"Paper here." Shen Qi spread his palms again.

Hiss.

Lin Xingyu tore off a page from his draft book and handed it to Shen Qi.

Thinking that one page of draft paper should not be enough, Lin Xingyu tore up a few sheets.

"A piece of draft paper is enough." Shen Qi waved his hand, holding a pen to deduce on the draft paper.

In this atomic laser cooling experiment, the minimum temperature value needs to be calculated, and the amount of calculation is not large, but the derivation steps are relatively cumbersome. Shen Qi has to make a draft, and he must properly grasp the scale according to the actual situation.

Swipe.

Shen Qi moved his pen like flying, and quickly filled both sides of the draft paper.

"Huh...so that's the case." Shen Qi raised his head and let out a sigh of relief, twisted his neck, and it was done.

Teacher Mu noticed Shen Qi: "It seems that Shen Qi has already got results?"

Snapped.

Shen Qi snapped his fingers: "Yes."

slap.

Teacher Mu snapped his fingers with his left and right hands: "Then, Shen Qi, please show your results."

After wiping off the submarine question on the blackboard, Teacher Mu asked Shen Qi to come up to the stage to answer.

Shen Qi came to the stage and started to write on the blackboard with a piece of chalk.

The first step in this question is to get the frequency of the laser, according to the classic Doppler effect:

ω(1+vx/c)

In fact, it is impossible for Doppler himself to realize that the theoretical effect he put forward in a flash of inspiration was widely used in various countries and fields all over the world one or two hundred years later.

Today's color ultrasound in hospitals is based on the Doppler effect, which is also widely used in the military, as well as at the atomic microscopic level.

Shen Qi ordered Doppler to open an exit for the vanguard officer. Combined with the setting of the topic, the Doppler vanguard officer entered the enemy camp and launched a surprise attack first.

If the electrons are bombarded towards us with a positive velocity v, a backward motion can be obtained, and the lateral dimension of the whole figure will be reduced in the ratio of c-v to c.

Shen Qi can calculate an electric field after taking the second derivative. When high-energy electrons pass through, they emit radiation in the forward direction. Task.

Next it was General de Broglie's turn to go out.

De Broglie has actually touched on the preliminary quantum mechanics. The high school physics textbooks do not talk about it in general, but the essence is written in the textbooks, but there are many conclusive descriptions and few specific explanations.

Shen Qiling de Broglie General Ma Tiao Company, he gave the momentum of an atom absorbing a photon on the blackboard as:

ω0/c

Assuming that the temperature is T, the corresponding de Broglie wavelength is:

λ=/root sign mkT

Wavenumber is the rate of change of phase to distance, frequency is the rate of change of phase to time, ω and k are similar to time and space in one spatial direction.

Mr. Steven Zhu used a three-dimensional laser beam to form a magneto-optical trap to trap atoms in a small space for cooling. The 3D animation played by Mr. Mu just now simply simulated the experimental process. The propagation of light in three-dimensional space interacts with atoms and absorbs The number of atoms behind the photons, and the momentum generated by each absorption and radiation of the atoms surfaced... Shen Qi filled the blackboard on the left, and the solution process was nearly half completed.

Teacher Mu remained on the sidelines quietly, and in front of Lin Xingyu in the audience was the draft that Shen Qi had typed just now.

Lin Xingyu looked down at Shen Qi's draft, and looked up at the solution process on the blackboard. This was wrong. The draft Shen Qi typed was different from what he wrote on the blackboard.

Lin Xingyu could basically understand more than half of the content on the blackboard, but when he looked at Shen Qi's draft paper, he couldn't understand it at all.

Because what Shen Qi wrote on the draft paper were relatively independent core steps, his thinking was too jumpy, and few people except himself could understand what he wanted to express.

Shen Qi took the core steps as the outline, and started a detailed solution on the blackboard. Soon, the answer will come out soon.