The Quantum Trinity was released, produced by Pan Jianwei, Zhao Bo and others

Three Bodies fans are in luck! The animation of "Three Bodies" is scheduled to air on December 3, 2022, which is long awaited by all fans. On December 2, quantum physicists and quantum chemists have been waiting for the long-awaited "Quantum Three Bodies" to be "released" first!

 

 

The team of Jianwei Pan and Bo Zhao at the University of Science and Technology of China (USTC) recently accomplished an important breakthrough in which they have, for the first time in the international arena, controllably synthesized ultracold gases of triatomic molecules (i.e., molecules composed of three atoms) at temperatures as low as 100 nK, i.e., only 10-17 degrees above absolute zero, with a molecule whose phase space density is 10 orders of magnitude higher than that of the triatomic molecular gases previously obtained by direct cooling. This work provides a platform for the study of quantum three-body problems and opens new paths for quantum simulations and ultracold chemistry. The research paper was published today in the prestigious international journal Science.

 

01Probing chemistry at the quantum level

 

Our world is made up of atoms, and tiny atoms are in motion all the time. It is the movement of these countless "gizmos" in the quantum world, and their interlocking and interconnectedness, that gives our world its molecules, its diverse substances, and even its life, intelligence, and civilization. Nature is so beautiful, and behind all the colorful and complicated phenomena and changes, there is such a simple and concise reason: the constant movement and interaction of atoms.

 

So, when we look at the mountains and the seas and the wilderness, when we feel the breeze or the sun, do we also want to gain a deeper insight into the secrets of the "Creator": how do atoms form the richness of the world?

 

The story of atoms, molecules and how they interact is "chemistry".

 

Chemistry has gone through several different stages as understanding has grown and technology has advanced.

 

(Image from the internet)

 

The early days of chemistry were witnessed by test tubes, beakers, and alcohol lamps, and the birth of quantum mechanics in the early 20th century brought chemistry to a whole new stage. It was realized that the nuclei and electrons of atomic molecules obeyed quantum mechanics and that chemical reactions could be described by a multi-particle Schrödinger equation containing the motion of nuclei, electrons, and the Coulomb interaction between them. The essence of chemical reactions is the spatial distribution and variation of electron clouds and the motion of atomic nuclei. Chemistry had a solid theoretical basis, and quantum chemistry emerged.

 

 

In the second half of the 20th century, thanks to the development of computers, chemical reactions could be studied using numerical computational methods, and computational quantum chemistry developed. On the other hand, the emergence of new experimental techniques, such as the molecular beam technique developed by Hirschbach and Yuanzhe Li in the 1980s, led to a deeper understanding of molecular interactions and reactions, etc. Theory and experiments are mutually reinforcing, and together they have greatly contributed to the progress of quantum chemistry.

 

(Image from the internet)

 

Chemical reactions are quantum in nature, and even a simple chemical reaction that we are familiar with in junior high school is described by quantum mechanics. But chemical reactions usually occur at high temperatures, where the de Broglie wavelengths of molecules are very short, which makes the quantum mechanical effects in the reaction difficult to observe.

 

We want atomic molecules to slow down and slow down again, so that we can "see" the quantum mechanical behavior of the reactions more clearly. We want to be able to actively and finely manipulate the atomic molecules so that they collide with each other and react according to the script we envision. In this way, we will not only see the end product, but also gain insight into the intermediate processes.

 

Controlled ultracold quantum chemistry was born.

 

A corner of the quantum triplet "shooting scene" at China University of Science and Technology

 

The never-ending thermal motion of atoms in the microscopic world is manifested in temperature at the macroscopic level. Now, in winter, we huddle up and don't want to move, but the temperature is simply too high for the atoms, which are moving at rates of up to several hundred meters per second!

 

Reducing the speed at which atoms move is reducing their temperature. Over the past few decades, various experimental techniques have been developed to cool and imprison these restless "elves". To tame them and keep them from doing what they want!

 

 

 

Quiet atomic molecules escape the noise of the tropics and reveal their quantum properties in a more distinct way. In this way, we can see the law of creation and develop and improve our atomic molecular theory. It can be seen that controlled ultracold quantum chemistry is a completely new stage of quantum chemistry.

 

02The "trilogy" of quantum triplets

 

How to obtain ultracold atoms and ultracold molecules?

 

By using laser technology, it is possible to exchange the momentum between photons and atoms, thus cooling them. This is the laser cooling technology. The laser cooling technology of atoms is already mature, and combined with magneto-optical traps and evaporative cooling, people have prepared ultracold atomic gases with low temperature and high density.

 

Can one go further and achieve laser cooling of molecules? Things are not so simple. This is because laser cooling requires a condition: there must be a "cyclic jump" in the energy level, so that the cooling can continue and the temperature can be continuously lowered. In molecules, cyclic jumps are usually not present due to the presence of oscillatory energy levels. At present, only a few molecules have been found to have approximate cyclic jumps.

 

After many efforts and attempts on the path of direct cooling of molecules, the best result in the world so far for polyatomic molecules is the cooling of CaOH molecules to 100 μK with a phase space density of about 10-12.

 

There is another path, which is to start with supercooled atoms, and go step by step to synthesize supercooled molecules in this way, starting from one life to two and two to three. Back in the 1980s, scientists used light to synthesize diatomic molecules from cold atomic gases, but this method yielded molecular gases with low densities and high temperatures. "There is no way out of the mountain, but there is another village in the dark". Scientists explored another technique in ultracold atoms - Feshbach resonance technique, and using this technique, scientists finally prepared diatomic molecular gas with high density and low temperature . The so-called Feshbach resonance means that atoms scattering will be drawn together to form weakly bound molecules, and if the energy of the scattered and bound states are the same, resonance will occur, which will greatly enhance the strength of the coupling between the two states. Moreover, the Feshbach resonance can be modulated by an applied magnetic field, which gives us a new opportunity to use the magnetic field to synthesize atoms into molecules.

 

The leap from "two" to "three" is another qualitative one, where three means more and more complex.

 

The three-body problem is a well known puzzle in mathematics and physics. The classical three-body problem in celestial mechanics has been a headache, it can not be solved precisely, there are chaotic effects, so the "three-body civilization" in the novel "Three Bodies" after more than a hundred times destruction and rebirth, and finally had to escape from the home planet to visit the distant Earth. The quantum and the three bodies known for burning the brain "a meeting of the golden wind and the dew, it will be difficult to fall countless people". Quantum three body problem, really difficult

 

There is no reliable theoretical prediction on the nature of triatomic molecules and whether they can be synthesized. In the absence of theoretical guidance, the step towards triatomic molecules is like walking in a deep valley with trees and dark currents at night, and one can only tell where the road is by the hazy light and the faint wind.

 

The research team of CSU knows the difficulties and has been working in this field for many years. As we all know, "Three Bodies" is a trilogy, and the quantum three bodies of CSU has also completed the "trilogy" of NS top issue (Nature, Science).

 

Is there an observable Feshbach resonance in atom-molecule collisions? 2019, a research team at CSU gave a positive answer, as they observed the Feshbach resonance of atoms (40K) and diatomic molecules (23Na40K) at ultra-low temperatures for the first time in the world.

 

Science, 2019

 

Based on the 2019 work, near the Feshbach resonance, the team couples the scattered state of atomic molecules directly to the bound state of triatomic molecules via an RF field. The 23Na40K molecular loss spectrum resulting from RF synthesis of triatomic molecules gives indirect evidence for the synthesis of triatomic molecules.

 

Nature, February 2022

 

In just under a year, the quantum triplet story went even further: first a simplified atom-biatom molecular mixture was prepared, which allowed the team to synthesize 40K atoms and 23Na40K molecules into triatomic molecules by the Feshbach resonance magnetic conjugation method. Ultimately, an ultracold molecular gas containing 4,000 23Na40K molecules at temperatures as low as 100 nK was obtained - far superior to the results of directly cooled triatomic molecules, both in temperature and phase space density.

 

By RF dissociating the triatomic molecules and observing the behavior of the dissociation spectrum, the research team obtained direct and definitive evidence for the synthesis of triatomic molecules.

 

Science, December 2022

 

03Conclusion: Toward a higher "level of civilization"

 

The successful preparation of ultracold triatomic molecular gas is a milestone in the field of ultracold molecules and ultracold chemistry, and a new beginning that will open up new opportunities for the entire field of ultracold quantum. For example, it can be used as a basis to explore the quantum three-body problem; it also helps people to gain fundamental insight into the secrets of ultracold reactions; due to the molecule's rich and unique energy level structure, it also has potential applications in fields such as quantum information processing and quantum precision measurement ......

 

In the novel "Three Bodies", the "three-body civilization", which can conduct large-scale interstellar voyages, is already highly civilized in the eyes of Earthlings, but from a higher perspective, it is still in the primary stage of civilization, and there are civilizations such as the Singers and the Zeroes above it. The "quantum triplet" is also the beginning of a promising ultra-cold quantum chemistry, and it is reasonable to expect that the field of ultra-cold chemistry will continue to develop and move to a higher "civilizational level".