Chapter 360 This chapter actually reveals a truth (Part 1)
Cold atom research.
It is not difficult to see from the literal meaning that this refers to the study of atoms under ultra-low temperature conditions.
Students who did not fail high school chemistry should know this.
The most direct reflection of the temperature of an atom is the speed of the atom.
That is to say, there is a positive correlation between the two.
At room temperature.
The atoms move very fast, sliding around like Yasuo, and the question marks can't keep up with them.
To study the physical properties of atoms, we need a stable single atom or a group of atoms that will not wander around.
so what.
When studying atoms, it is necessary to cool them down, that is, to 'freeze' them.
Typically, research requires atomic temperatures in the vicinity of μK.
However, due to cost issues, in many cases the entire experimental device is not required to be at a temperature of μK.
Therefore, normal research groups working on cold atoms will use lasers to cool atoms.
That is, cooling a very small area.
In later generations, some Japanese food restaurants also liked to do this kind of work, but they did not cool it but heated it - roasting the middle part of a piece of fresh beef and leaving the other parts raw. It was euphemistically called "Sizzling Heart Beef Sashimi".
Xu Yun doesn’t have much prejudice against this way of eating, but for more than 50 yuan per piece, it challenges the bottom line of people’s IQ
The topic returns to its original place.
At present, most of the principles for cooling lasers are Doppler cooling, which is relatively complex and will not be described in detail here.
In short, this thing can reduce the temperature of atoms to very low.
But the final result of cooling is just to slow down the atoms. Although the atoms slow down, they are still scattered disorderly throughout the cooling area.
It's like you have demarcated a long highway and made all the cars in it lose power and stop in place. But if you want to study these cars, you need to gather them together.
So at this time, another technical method is needed.
That is the magneto-optical trap.
The magneto-optical trap is referred to as the magneto-optical trap, code-named MOT.
Among the top 100 microscopic experiments selected by Nature magazine in 2019, the magneto-optical trap ranked 58th. It is a very, very exquisite experimental design.
It uses magnetic fields and light fields to slowly make particles controllable and aggregated.
The specific method of MOT is to install a pair of anti-Helmholtz coils in the z direction, so that the magnetic field is distributed along the radial direction in the xy plane.
The magnetic field in the positive center is 0. Where the magnetic field is not 0, Zeeman splitting will occur.
The energy level of Zeeman splitting is ΔE=gμBBz/, and the size of the energy level splitting is related to the size of the magnetic field, and the size of the magnetic field is related to the spatial position.
Therefore, in the presence of MOT, the two-level atom will experience a force of Fmot.
At this time, two opposing beams of circularly polarized light are applied. When the magnetic field is forward, compared with the σ+ light, the σ- light has less detuning and is closer to resonating with the atoms.
Therefore, the atoms will move along the σ-light propagation direction to a position where the magnetic field is close to 0.
The opposite is true where the magnetic field is negative, and the atoms will eventually be pushed to a place where the magnetic field is close to 0.
final.
The atom will be trapped at the point where the magnetic field is 0.
This principle is very simple and easy to understand.
MOT can gather a lot of atoms, approximately tens of millions or more at a time. At the same time, the atomic density will be relatively high, about 10^9/cm^3.
It's like a forklift pushing all the cars parked on the highway together.
Of course.
The experimental object of traditional MOT is atoms. During the experiment, all atomic gases are added - yes, they are all gases. (I don’t know if the concept of gaseous metal atoms is mentioned in current textbooks, but it seems to be there)
Unlike atoms, Xu Yun and the others need to consider isolated point particles this time.
The two cannot be compared in terms of volume or difficulty, but the solitary point particles are also electrically neutral, so the solitary point particles are among the very few particles that can be condensed using the MOT principle.
But after all, this is only theoretically feasible.
Whether the isolated point particle can be successfully brought to the ground state depends on the final practical operation.
"Professor Lu."
Beside the operating table, Xu Yun was introducing his experimental ideas to Lu Chaoyang:
"My idea is this. First, we use evanescent waves to construct a light field with uneven light intensity inside the beam channel."
"Then, according to the light field distribution, we lay out the electric field with the same trend."
"In this way, the difference in the dipole force generated by the evanescent wave at each point will cause the particles to 'bounce' non-stop."
"Each time we 'bounce', we slightly lower the trapping electric field. The electrostatic repulsion between atoms will cause the charged particles to spread out, and the outer particles will escape."
"As for the isolated point particles, since they have no static mass and no charge, they will be permanently stored in the channel."
In layman's terms, Xu Yun's plan is comparable to shaking a dustpan in reality.
The particles after the collision of lead ions are equivalent to a mixture mixed with soil, seeds, bugs, and weeds.
The best way to sort them is to shake a dustpan.
As long as you design the appropriate hole size, you will always be able to shake out what you need in the end - nothing more than the specific strength and hole diameter.
Of course.
This explanation is just for the convenience of understanding. For industry insiders like Lu Chaoyang, there is much more to consider than just jitter.
He was silent for a moment, then looked up at Xu Yun:
"The idea is generally feasible, but Xiao Xu, I have a question."
Lu Chaoyang said that he stretched out an index finger on each of his left and right hands, and touched the fingertips:
"You see, the contact between fingertips is like two beams colliding with each other. There is no debate in this link, but"
Then Lu Chaoyang straightened the originally curled thumb of his left hand, forming an equals sign with the extended index finger, and then the surfaces of the two fingers touched each other:
"But Xiao Xu, have you ever considered that lead ions in the same beam, that is, moving in the same direction, may collide or be excited due to the electric field?"
"If internal heavy ions collide, the subsequent direction will be uncontrollable."
A boy who was doing the work next to him heard this and nodded in agreement.
Lu Chaoyang's question is also not difficult to understand.
Just like on a frontal battlefield, two armies are launching missiles at each other, and the trajectories of each other's missiles are directed towards each other.
But if the missile is flying, there is suddenly an extra force between the sky and the earth from the non-moving direction, and this force is large enough to affect the trajectory of the missile
In this case, a situation is likely to occur:
Before encountering the enemy missile, the missile's course was changed first and an internal collision occurred.
Although the consequences of such a collision are also explosions, they are obviously of no value - the purpose of launching missiles is to kill the enemy, not simply to watch fireworks.
Therefore this situation
It really has to be taken into account.
Otherwise, the entire experiment would become a joke, and Xu Yun's prestige would be greatly affected.
However, Xu Yun was obviously prepared for this situation. He picked up a pen and quickly wrote a formula on the paper:
ψ∝exp(|x|/x0).
Then he drew a horizontal line under the expression and stopped talking.
Looking at this gesture, a hint of astonishment appeared in Lu Chaoyang's eyes:
"This is."
A few seconds passed.
He suddenly let out an oops and slapped his forehead hard:
"Oh, look, why did I forget the delta potential well? OK, Xiao Xu, then I have no problem."
The expression on Xu Yun's face did not change, but the slightly raised corners of his mouth still vaguely revealed his inner pride.
That's right.
Smart classmates must have figured it out.
The formula above is exactly the wave function of the bound state of a single atom in one-dimensional space.
According to this wave function, a situation can be clearly judged:
When the distance between two atoms is less than twice the atomic radius, the energy of the antisymmetric state E>0, and the energy of the symmetric state =0.
The energy of free electrons is also 0.
This means that in this case, the symmetry state is already unstable and the electron can fly to infinity.
Therefore, when two lead ions come close to each other, they naturally break up rather than collide.
It is at this point that they cannot be considered bosons.
The energy of decomposition and the energy of collision are two completely different magnitudes.
But then again.
Lu Chaoyang's misjudgment has little to do with his ability, but with the direction of the experiment.
In fact, particle physics experiments do not include Bose-Einstein condensates. In a sense, the two can even be said to be two extremes.
If it weren't for the special characteristics of solitary point particles, Lu Chaoyang would never be exposed to this aspect at all.
So it's normal for him to make some mistakes in thinking.
The more you differentiate, the clearer it becomes.
Xu Yun then discussed some process issues with Lu Chaoyang, and once everything was correct, they began to set up the experiment.
The production of cold atoms requires a high level of vacuum, generally around 1x10^-10mbar.
Fortunately, this is not 1850, so it is not difficult to create such a vacuum environment.
"Dr. Tang Fei."
Xu Yun looked at the roster in his hand and read out a name:
"I'll leave you to arrange the anti-Helmholtz coil."
The Tang Fei in Xu Yun's mouth is a man in his early thirties, wearing a pair of gold-rimmed glasses and short hair. He looks very capable.
Tang Fei is the youngest member of the entire project team after Lu Chaoyang. He is also a doctoral student trained by the University of Science and Technology. He is now a cutting-edge backbone of a research institute at the University of Science and Technology.
In fact, with Xu Yun's current status, he cannot hire seniors like Tang Fei who have already graduated and are working and have high abilities.
It just so happened that Tang Fei was currently in the critical period of being promoted as an associate researcher and needed some exposure and achievements to enrich his resume.
So through the introduction of Academician Pan, I successfully joined Xu Yun's group, letting Xu Yun catch him.
And even if they are divided into groups in the future, he will follow Xu Yun to work on projects.
Now that he received Xu Yun's instructions, Tang Fei immediately straightened his expression:
"No problem, leave it to me." (It's a fun thing to say. If I hadn't corrected the typo during verification, you would have seen 'Marry me'.)
After Tang Fei left.
Xu Yun continued to issue instructions:
"Li Ruo'an, you are responsible for debugging the radio frequency field."
"Received!"
"Dr. Yang Kun, take charge of the evanescent wave."
"Understood!"
"Senior Zhang Han, you are responsible for observing wave packets - remember to set the parameters to odd multiples of 13.2."
"Okay!"
"Sister Ye Zhi, go order takeout. You decide the taste. You don't want celery or coriander."
"OK!"
After allocating tasks.
Xu Yun and Lu Chaoyang waited at the console together.
In order to ensure that the project team can obtain efficient positive feedback after refining the division of labor these days, many project teams have gradually begun to be equipped with spreaders:
This thing is about the size of two one-dollar coins, with a button and an anti-accidental touch switch on it.
After completing the task, release the anti-accidental touch switch and press the button again. A green dot will appear under the corresponding item on the main display, prompting the person in charge that the task of block XX has been completed.
It is said that the project team of a certain university in Yanjing also used the voice package of pangolin, which is so magical.
Xu Yun's research team this time was equipped with a spread system.
over time.
The seven light spots in front of Xu Yun gradually turned from red to green.
About twenty minutes passed.
All the light spots turned green, and Lu Chaoyang on the side snapped his fingers:
"OK, Xiao Xu, you can summon the Dragon Balls."
Xu Yun: "."
Ignoring the funny guy next to him, Xu Yun took a deep breath and said through the main microphone:
"Attention, members, the ground state experiment of the lone point particle is about to begin, countdown to 32.1"
"Start!"
The moment I finished speaking and started.
Xu Yun pressed the switch on the main console.
Buzz buzz——
A beam with an order of magnitude smaller density than the first time rushes out of the beam tube.
And it's different from the first time.
Within 10^-12 seconds, a preset evanescent wave field enveloped them.
Phew~
A radiation pressure invisible to the naked eye appears.
at the same time.
The first wave of lead ions begins to collide.
Bang——
The two lead ions exploded instantly like Kennedy's head, and all kinds of things flew out.
Then another 10^-12 seconds passed.
When the anti-Helmholtz coil is energized, a magnetic field with the same intensity as the evanescent wave arrives.
A large number of particles began to detune, flying out of orbit one after another.
The flying particles are guided to the target, and finally end up as electrons or photons.
Except for a few electrically neutral elementary particles:
Neutrinos, gluons, photons, Higgs particles, Z bosons.
These five kinds of particles are either impossible to capture or very difficult to capture, and they will leave the channel on their own initiative.
In addition to basic particles.
There are only a few other electrically neutral composite particles left, and there are very few types.
For example, a neutron consists of an up quark with a charge of +23 and two down quarks with a charge of 13.
Another example is X-ray particles.
The essence of X-ray particles is actually photons, so you can ignore them.
Neutrons can be absorbed by boron-containing polyethylene - this is a low-level radiation capture and will not cause nuclear fission
When a series of operations are completed.
There is another uncharged composite particle left in the channel.
It's called.
Λ hyperon.
Code name
4685. (End of chapter)