fifth state
UNAM laboratory (Photo: Courtesy of Jorge Amin Seman Harutinian)

In his laboratory, Jorge Amin Seman Harutinian, a researcher from the Institute of Physics at the National Autonomous University of Mexico (UNAM), has achieved the coldest temperatures in the universe.

“We’ve been at 20 billionths of a degree above absolute zero. As far as we know, there is no place where that temperature level can be achieved naturally. We dare say that the coldest known place in the entire universe is on planet Earth, in laboratories like ours,” he says in an interview with Tec Review.

The story of this experimental feat began in 2014, when Seman was hired by the UNAM as a researcher.

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He then began to take over the projects of the Ultracold Matter Laboratory (LMU), the country’s first quantum gas laboratory. At the end of 2018, he managed to obtain a Bose-Einstein condensate for the first time in Mexico. This is colloquially known as the fifth state of matter, due to its properties that cannot be framed as manifestations of the four most well-known aggregate states: solid, liquid, gas, and plasma.

“Since then, we’ve been working hard and started doing some experiments that we haven’t been able to complete, especially now that the University and our laboratory are closed. As we can’t make a contribution towards the Covid-19 crisis, we had to stop. And that’s where we are,” Seman explains.

More than two decades ago, U.S. researchers had managed to produce a Bose-Einstein condensate. They established the experimental guidelines on which Seman and dozens of researchers around the world have relied to design strategies for obtaining these peculiar fluids.

In an interview with Tec Review, Victor Manuel Romero Rochín, a researcher at the UNAM’s Physics Institute, tells us that it was in 1995 when two groups of U.S. scientists, one in Colorado and one in Massachusetts, obtained Bose-Einstein condensates for the first time in the world by cooling rubidium and sodium gases, respectively, to very low temperatures.

This achievement concurred with a prediction made by German-born scientist Albert Einstein in 1926, after having worked with Indian-born researcher Satyendra Nath Bose on certain gases that would acquire surprising attributes upon being cooled to a very low temperature, almost absolute zero.

“They’re called Bose–Einstein condensates because those two had predicted them in theory. They’re superfluids, i.e. fluids that are not like fluids such as water. These new fluids have no viscosity. They behave in a very peculiar way. If a liquid could be made of these substances, it could flow without end,” says Romero Rochín.

He also explains that all liquids we know have viscosity. Honey, for example, has a lot of it. Air also has viscosity, not much, but it’s there; otherwise, planes wouldn’t fly.

Strange things happen at the low temperatures in which this so-called fifth state of matter exists: the principles of quantum physics begin to play a predominant role rather than the laws of classical physics that govern movements such as how rain falls or the orbits of the planets around the Sun.

According to Seman, as the temperature drops, atoms tend to behave as if they were waves, then they begin to constructively interfere with one another and form a macroscopic matter wave.

This is what we call the Bose–Einstein condensate, in which it is often said that all the atoms behave as if they were one. “In reality, they behave like a single collective wave in which all the atoms contribute at the same time, and one can’t be distinguished from another.”

To date, only tiny quantities of Bose–Einstein condensates, equivalent to the volumes of small droplets, have been obtained in the world. However, it is expected that technology will soon be developed that can generate larger quantities.

In the 2018 experiments by Seman and his team of collaborators, everything was performed in an ultra-high vacuum chamber where there was only a sample of a gas inside. Obviously, this couldn’t be touched, because if it were, it would have been warmed by the contact of fingers. This was an experiment that involved the mastery of complex techniques such as magnetic field generation and laser light with very specific properties.

“The gas, in our case lithium, the third element on the periodic table, was trapped in magnetic fields. Normally, matter absorbs energy from light and heats up, but if one understands this process of energy exchange, it can be configured so that the exchange occurs in the opposite direction, so that it’s the light that takes energy from the atoms and not the other way around. This is the most important technique we use for cooling. It also means knowing very well how to generate the correct power, polarization, and color of laser light so that this process occurs in the opposite-to-normal direction,” Seman says.

 

The Quantum Background

As a theoretical prelude, it’s important to point out that there are two large families of subatomic particles: fermions and bosons.

The first group has a semi-integer (1/2, 3/2…) spin (measurement of the rotation of an elementary particle) and the second group has an integer spin (0, 1, 2…). Fermions have the quality of not being able to occupy equal quantum states in a system, while bosons can. Quantum states refer to the numbers that describe the state of a particle. There are several of these numbers, and they depend on the system in question.

This concurs with what Fernando Ángeles Uribe, coordinator of the School of Science’s Control and Electronics Workshop at the UNAM, said in an interview with Tec Review. He also uses metaphorical figures to explain the Bose–Einstein condensate as follows:

Fermions do the same thing as people who want to stand out at a gala party: no one else can be dressed the same because there would be rivalry, something that would be forbidden. In physics, this law is called the Pauli exclusion principle. If another person shows up dressed the same, the other will do his or her best to change clothes (quantum numbers). Conversely, bosons are like people who don’t worry about attracting looks from others: they really don’t care if they go to a party dressed the same as someone else.

According to this expert, when the energy of a system is lowered, the quantum numbers of the particles are altered, and because they don’t have the energy to change their states, “it becomes inevitable that particles will begin to occupy states with the same quantum numbers since they have very little energy left and cannot be subject to the Pauli exclusion principle.”

The equivalent, according to the party metaphor, is that the level of rivalry drops. This happens when, for example, people go to a party in which it’s required that everyone dress the same and the privilege of standing out in different attire is granted only to the host.

In conclusion, a Bose–Einstein condensate is a state of matter (the fifth, according to popular jargon) belonging to the quantum system, i.e. it is subject to the theory related to the discontinuous emission and absorption of energy.

According to Rosario Paredes Gutiérrez, a researcher from the Physics Institute at the UNAM, the main feature of this state is that the majority of its elementary constituents are found in the lowest state of energy.

“When we say “majority”, it means an enormous number of constituents, say 1,000,000,000. For example, a grain of salt has about 10^{19} (a 1 followed by 19 zeros) molecules of NaCl (sodium chloride). Belonging to the quantum system also implies that the atoms or elementary constituents, in addition to showing dual wave and particle behavior, are governed according to one of the two modes, fermionic or bosonic. This categorization associated with an odd or even number of particles, respectively, has major implications for the state in which large clusters of elementary constituents can be formed,” says the researcher.

According to Paredes Gutierrez, while a sample of fermion atoms is such that only one quantum state can be occupied at the same time, in the case of boson atoms, they can all occupy the same quantum state at the same time. Hence the base state can be populated macroscopically, which was precisely Bose and Einstein’s theoretical discovery in 1925.

The theoretical contribution of these great scientists from the last century has given rise to extraordinary applications, “because as is well known, all matter is made up of atoms and molecules that behave according to quantum mechanics,” comments Paredes.

 

A Major Budding Technological Transformation

One of the most important applications of cold atoms is metrology, the science of measuring of physical quantities to great precision.

“Atomic clocks have already been developed whose ticking mechanism is cold atoms, not as cold as those of a Bose–Einstein condensate, but the techniques used to produce this cold gas are the same,” says Seman.

Because the atoms are very cold in these clocks, they behave very similarly because they have very little energy. Seman explains that the vibration of the electrons within these atoms is exactly the same for all of them, and when synchronized it produces an ultra-precise tick.

“A good quartz watch falls behind a few minutes a year, so it needs to be corrected a little bit and it’s more than good enough for daily life. But in telecommunications, it takes a more precise clock to synchronize millions of signals simultaneously, and the only way to do this is through very precise time control, and only one of these clocks allows this. In our daily lives, we use this technology in GPS instruments based on satellite signals synchronized with atomic clocks,” says Seman.

Romero has a similar opinion. He comments that Bose–Einstein condensates have already opened the door to making atomic clocks even more precise than the ones we have now, which will allow for the development of more and better communications. “They could also lead to a quantum computer or better measurements of gravimetry that could lead to a greater understanding of what the land is like so that we could find oilfields more easily.”

Although this new state of matter broadens the horizon of new technological developments, the problem is that it’s still difficult to achieve because the temperature must be lowered enormously with specialized techniques to levels close to absolute zero. “It takes an entire lab to cool a droplet of gas. Maybe in the future we’ll be able to cool liters more easily,” says Romero.

The Underlying Philosophy and Passion

Although science is neutral, because it doesn’t signify any particular social transformation, according to Camilo Camhaji García, a mathematician and specialist in science philosophy at the UNAM, manipulation in terms of the discovery of a new state of matter gives humanity an ever greater strength in its ability to understand nature, which is analogous to the paradigm shifts that occurred in the scientific revolutions of previous centuries.

“It’s comparable to the discovery in the 19th and 20th centuries of the different atoms that make up the elements, leaving behind the ancient theories of the four elements: earth, water, air, and fire. The so-called theory of the fifth state of matter and the technical resources to generate it demonstrate a new viewpoint that helps us understand phenomena on the boundary between physics and chemistry,” says the mathematician in interview with Tec Review.

This is how these two natural sciences, in terms of quantum physics, increasingly become a single unified field of study, which, according to Camhaji, can only translate into a deeper, more exciting and passionate understanding of the total structure of the universe.

It’s precisely due to these last concepts, closer to the heart than to reason, that Seman describes the spiritual background that led him to becoming the first Mexican to obtain a Bose–Einstein condensate.

“Science is for the passionate. People who do science aren’t necessarily thinking about making money. Those who choose to start out on the path of science are excited when they learn and discover new things, when they see that nature and the universe are more intricate than expected,” says Seman.

“Because the goal of science is always to understand or to do something that hasn’t been done by anyone before. As this is, in principle, very difficult, the level of emotion and satisfaction is high when you succeed.”

 

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