Into Unscientific

Cold Atom Research.

It is not difficult to see from the words that this refers to the work of studying atoms at ultra-low temperatures.

Students who did not fail in high school chemistry should know.

The temperature of an atom is most directly reflected by its velocity.

That is, the two are positively correlated.

Room temperature.

The atomic movement speed is very fast, sliding around like Yasuo, and the question marks can't keep up with them.

To study the physical properties of atoms, a stable single atom or group of atoms is needed that will not run around.

so what.

When studying atoms, it is necessary to cool down the atoms, that is, to 'freeze' them.

Typically, studies require atoms at temperatures around μK.

However, due to cost issues, it is often not necessary for the entire experimental device to be at a temperature of μK.

Therefore, normal research groups working on cold atoms will use lasers to cool atoms.

That is, a very small area is cooled.

Some Japanese grocery stores in later generations also like to do this kind of work, but instead of cooling it, they heat it up—the middle part of a piece of fresh beef is roasted, and the other parts are raw, which is called heart-burning beef sashimi.

Xu Yun doesn’t have much prejudice in this way of eating, but it’s a challenge to the bottom line of people’s IQ if they cost more than 50 yuan for a slice.

The topic is back to the original place.

At present, the principle of cooling laser is mostly Doppler cooling, and the principle is relatively complicated, so I won’t go into details here.

In short, this thing can reduce the temperature of atoms to very low.

But the final result of cooling down is just to slow down the atoms. Although the atoms slow down, they are still scattered in disorder in the cooling area.

It's like you have delineated a long highway and let 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, it is necessary to use another technical means.

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, which is a very, very delicate experimental design.

It uses the magnetic field and light field to slowly make the particles controllable and gather together.

The specific method of MOT is to install a pair of anti-Helmholtz coils in the z direction, and then on the xy plane is a magnetic field distributed along the radial direction.

The positive central magnetic field is 0, and Zeeman splitting will occur in the place where the magnetic field is not 0.

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.

So in the presence of MOT, the two-level atom will experience a force of Fmot.

At this time, two opposite beams of circularly polarized light are applied. When the magnetic field is positive, the σ- light has a smaller detuning than the σ+ light, and is closer to the resonance of the atom.

Therefore, the atoms will move along the σ-light propagation direction to the position where the magnetic field is close to zero.

Where the magnetic field is negative, the opposite is true, and the atoms will eventually be pushed to a place where the magnetic field is close to zero.

finally.

Atoms will be trapped at the point where the magnetic field is zero.

The principle is very simple and easy to understand.

MOT can gather a lot of atoms, and it can gather more than tens of millions of atoms at a time. At the same time, the atomic density will be relatively high, about 10^9/cm^3.

It is equivalent to having a forklift that 'pushes' all the cars parked on the highway together.

Of course.

The experimental object of traditional MOT is atoms, and all the atoms are added to the experiment—yes, they are all gases. (I don’t know if the concept of gaseous metal atoms has been mentioned in the current textbooks, but it should be there in my impression)

Unlike atoms, what Xu Yun and the others need to consider this time are lone point particles.

The two cannot be compared in terms of volume and difficulty, but the isolated point particles are also electrically neutral, so the isolated point particles are very few particles that can be condensed by the MOT principle.

But to say a thousand words and ten thousand words is only a theoretical feasibility after all.

Whether the isolated point particle can be successfully converted to the ground state depends on the final practical link.

"Professor Lu."

At the console, Xu Yun was introducing his experimental ideas to Lu Chaoyang:

"My idea is this. First, we use evanescent waves inside the beam channel to construct a light field with inhomogeneous light intensity."

"Then, according to the distribution of the light field, an electric field with the same trend is laid."

"In this way, the evanescent wave at each point produces a difference in dipole force, which will make the particles "bounce" non-stop."

"Every time we 'bounce', we slightly lower the trapping electric field, and the electrostatic repulsion between atoms will scatter the charged particles, and the outer particles will escape."

"The lone point particles, because they have no static mass and no charge, will be permanently stored in the channel."

Xu Yun's plan is compared to the dustpan shaker 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 out is to shake the dustpan.

As long as you design the appropriate hole size, you can always 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 people in the industry like Lu Chaoyang, there is much more to consider than just shaking.

He was silent for a moment, then looked up at Xu Yun:

"The idea is generally feasible, but Xiao Xu, I have a question."

Said that Lu Chaoyang stretched out an index finger on each of his left and right hands, and touched fingertips:

"Look, the contact between fingertips is like two beams colliding with each other. There is no dispute in this link, but"

Then Lu Chaoyang stretched out the originally curled thumb of his left hand, and formed an equal sign posture with the extended index finger, and then 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 the heavy ions inside collide, then the subsequent direction is uncontrollable."

Hearing the words, a boy next to him who was laying hands also nodded in agreement.

Lu Chaoyang's question is also not difficult to understand.

Just like on the frontal battlefield, the two armies are firing missiles at each other, and the trajectories of each other's missiles are aimed at each other.

But if during the flight of the missile, there is suddenly an additional force between the sky and the earth from a non-moving direction, and this force is large enough to affect the trajectory of the missile

In this way, a situation is likely to occur:

Before encountering the enemy's missile, the own missile's route was changed first, and an internal collision occurred.

Although the consequences of this kind of collision are also explosions, they are obviously of no value-the purpose of launching missiles is to kill and injure the enemy, not just to watch fireworks.

Therefore this situation

It really has to be taken into account.

Otherwise, the whole experiment would be a joke, and Xu Yun's prestige would be greatly affected.

However, Xu Yun was clearly prepared for this situation. He picked up a pen and quickly wrote down a formula on the paper:

ψ∝exp(|x|/x0).

Then he drew a horizontal line under the formula, and stopped talking.

Looking at this formula, a slight astonishment appeared in Lu Chaoyang's eyes:

"This is."

A few seconds passed.

He suddenly oopsed and patted his forehead heavily:

"Oh, look, how did I forget about the delta potential well, OKOK, Xiao Xu, then I'm fine."

The expression on Xu Yun's face didn't change, but the slightly raised corners of his mouth still faintly revealed his inner complacency.

That's right.

Smart classmates must have seen it.

The above formula is exactly the wave function of the bound state of a single atom in 1-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 is E\u003e0, and the energy of the symmetric state is equal to 0.

The energy of free electrons is also 0.

This means that in this case, the symmetric state is already unstable, and electrons can fly to infinity.

So when two lead ions come close, they naturally disintegrate rather than collide.

That is, at this time, they cannot be regarded as bosons.

The energy of decomposition and the energy of collision are completely different in magnitude.

But then again.

Lu Chaoyang's misjudgment has nothing to do with his ability, but with the direction involved in the experiment.

In fact, particle physics experiments do not include Bose-Einstein condensed matter, and the two can even be said to be two extremes in a sense.

If it weren't for the particularity of the isolated particle, Lu Chaoyang would never have been exposed to this aspect at all.

So it's normal for him to make some mistakes in thinking.

The more you discern the truth, the clearer you become.

Afterwards, Xu Yun and Lu Chaoyang discussed some procedural issues, and after they were correct, they began to set up the experiment.

The preparation of cold atoms requires a high-level vacuum, generally around 1x10^-10mbar.

Fortunately, today is not 1850, and it is not difficult to construct such a vacuum environment.

"Dr. Tang Fei."

Xu Yun glanced at the roster in his hand, and read a name:

"I'll trouble you to arrange the anti-Helmholtz coil."

The Tang Fei that Xu Yun said was a man in his early thirties, with a pair of gold-rimmed glasses and short hair, he looked very capable.

Tang Fei is a member of the entire project team who is second only to Lu Chaoyang in age. He is also a doctoral student trained by the University of Science and Technology, and is now a new backbone of a certain research institute of the University of Science and Technology.

In fact, with Xu Yun's current status, he would not be able to invite a senior like Tang Fei who has graduated and worked and is not low in ability.

It just so happens that Tang Fei is currently in the critical period of being promoted as an associate researcher, and needs some exposure and achievements to enrich his resume.

So he successfully joined Xu Yun's group through Academician Pan's introduction, and Xu Yun picked up a loophole.

And even in the future, even if they are grouped, he will follow Xu Yun to carry out projects.

Now receiving Xu Yun's instructions, Tang Fei quickly straightened his expression:

"No problem, leave it to me." (It's a fun thing to say, if I didn't correct the typo during the verification, you will see 'marry me'.)

After Tang Fei left.

Xu Yun continued to issue instructions:

"Li Ruo'an, you are in charge of debugging the radio frequency field."

"receive!"

"Dr. Yang Kun, you are in charge of the evanescent wave."

"clear!"

"Senior Zhang Han, you are responsible for observing the wave packets—remember to set the parameters to an odd multiple of 13.2."

"okay!"

"Sister Ye Zhi, you go to order takeaway, the taste is up to you, no celery and coriander."

"OK!"

After assigning tasks.

Xu Yun and Lu Chaoyang waited at the console.

In order to ensure that the project team can obtain high-efficiency positive feedback after refining the division of labor, many project teams have gradually begun to be equipped with spreaders:

It's about the size of two dollar coins, and has a button and a tamper-resistant switch on it.

After completing the task, release the anti-mistouch switch, and press the button again, and a green dot will appear under the corresponding item on the main display, prompting the person in charge to complete the XX block task.

It is said that the project team of a certain university in Yanjing also used the pangolin's voice package, which is magical.

Xu Yun's research team is equipped with a spread system.

over time.

The seven light spots in front of Xu Yun gradually changed from red to green.

After about twenty minutes or so.

All the light spots turned green, and Lu Chaoyang snapped his fingers:

"OK, Xiao Xu, you can summon Dragon Ball now."

Xu Yun: "."

Not caring about the teaser around him, Xu Yun took a deep breath and said through the main microphone:

"Attention all members, the ground state experiment of lone point particles is about to start now, the countdown is 32.1"

"start!"

At the moment of finishing speaking.

Xu Yun pressed the switch on the main console.

buzz buzz --

A beam with an order of magnitude density smaller than that of 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.

Shh~

A burst of radiation pressure invisible to the naked eye appears.

at the same time.

The first wave of lead ions began to collide.

Bang——

The two lead ions exploded instantly like Kennedy's head, and various things flew out of it.

Then another 10^-12 seconds passed.

When the anti-Helmholtz coil is energized, a magnetic field with the same strength as the evanescent wave descends.

A large number of particles began to detune, flying out of orbit one by one.

The flying particles are guided to hit the target, and finally end up as electrons or photons.

The exception is only 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 voluntarily leave the channel.

And except for the basic particles.

Only some other electrically neutral composite particles are left, and there are very few types.

For example, a neutron consists of a +23 up quark and two 13 down quarks.

Another example is X-ray particles.

Among them, the essence of X-ray particles is actually photons, so you can ignore them.

Neutrons can be absorbed by boron-containing polyethylene - this is low-level radiation capture and no nuclear fission will occur

After a series of operations are completed.

Another uncharged composite particle remains inside the channel.

it's called.

Λ hyperon.

code name

4685.