MTL - Into Unscientific-Chapter 360 This

  Chapter 360 This chapter actually reveals a truth (on)

  Cold atom research.

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

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

  The temperature of an atom, the most direct reflection is the velocity of the atom.

   That is, the two are positively correlated.

Room temperature.

  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 atomic group that will not run around.

so what.

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

  Usually, the research requires the temperature of the atoms to be around μK.

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

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

   is to cool a small area.

  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 a slice costs more than 50 yuan

  The topic returns to the original place.

  At present, most of the laser cooling principles are 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 only to slow down the atoms. Although the atoms have slowed down, they are still scattered disorderly 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, another technical method is needed.

   That is the magneto-optical trap.

   Magneto-optical trap is referred to as 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 utilizes 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 magnetic field at the positive center is 0, and Zeeman splitting will occur where the magnetic field is not 0.

  The energy level of Zeeman splitting is ΔE=gμBBz/, and the size of 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, compared with σ+ light, σ- light has a smaller detuning 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 0.

  The place where the magnetic field is negative is the opposite, 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 0.

  This principle is very simple and easy to understand.

  MOT can gather a lot of atoms, about ten million or more at a time, and 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 the traditional MOT is an atom, 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)

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

  The two cannot be considered the same 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 using the MOT principle.

   It’s just a thousand words and ten thousand words. After all, this is only a theoretical feasibility.

  Whether the ground state of the isolated particle can be successfully transformed depends on the final practical link.

   "Professor Lu."

  Beside 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, lay the electric field with the same trend."

   "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 will be permanently stored in the channel because they have no static mass and no chargeability."

  Xu Yun's proposal is in human language and in layman's terms, 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 classify them 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—it’s 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, they need to consider far more than simple 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."

   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 gesture with the extended index finger, and then touched the surface of the two fingers:

   "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 internal heavy ions collide, then the subsequent direction is uncontrollable."

  A boy next to him, who was fighting, also nodded in agreement when he heard the words.

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

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

   But if the missile is in the middle of its flight, 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 touching the enemy missile, the own missile was changed the route first, and an internal collision occurred.

  Although the consequence of this kind of collision is also an explosion, it is obviously of no value—the purpose of launching missiles is to kill and injure the enemy, not just to watch fireworks.

   Hence the case

   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 the 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 trace of astonishment appeared in Lu Chaoyang's eyes:

"This is."

   A few seconds passed.

  He suddenly oopsed and patted himself on the forehead:

   "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 self-satisfaction.

   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>0, 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.

  Particle physics experiments do not actually 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 clearer you become.

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

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

   Fortunately, today is not 1850, so it is not difficult to build such a vacuum environment.

   "Dr. Tang Fei."

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

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

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

   Tang Fei is the second-oldest member of the entire project team after Lu Chaoyang. 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.

  Actually, 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.

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

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

  Received 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 responsible for the debugging of the radio frequency field."

"receive!"

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

"clear!"

   "Senior Zhang Han, you are responsible for observing the wave packet—remember to set the parameter 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 the tasks are assigned.

  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:

   This thing is about the size of two one-dollar coins, and it has a button and a tamper-resistant switch on it.

  After completing the task, release the anti-mis-touch 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 voice package, which is magical.

  Xu Yun’s research team this time is equipped with a spread system.

Over time.

  The seven light spots in front of Xu Yun gradually changed 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 Dragon Ball now."

  Xu Yun: "."

   Ignoring the funny comparison around him, Xu Yun took a deep breath and said through the main microphone:

   "Attention all members, the ground state experiment of isolated point particles is about to start now, the countdown is three two. one"

"start!"

   At the moment of speaking and beginning.

  Xu Yun pressed the switch on the main console.

   buzz buzz —

   A beam with an order of magnitude density smaller than the first time rushes out of the beam tube.

   And different from the first time.

   Within 10^-12 seconds, a preset evanescent wave field enveloped them.

  咻~

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

at the same time.

   The first wave of lead ions begins to collide.

  Boom—

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

   Then another 10^-12 seconds passed.

  The anti-Helmholtz coil is energized, and 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 in the form of electrons or photons.

   Except for only a few electrically neutral elementary particles:

  Neutrino, Gluon, Photon, Higgs, Z boson.

  These five kinds of particles are either impossible to capture, or it is very difficult to capture, and they will voluntarily leave the channel.

   In addition to the basic particles.

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

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

   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 low-level radiation capture, and nuclear fission will not occur

   When a series of operations are completed.

Inside the    channel there remains another uncharged composite particle.

   It's called .

  Λ hyperon.

  Code

  4685.

  (end of this chapter)