- Alejandra Martins
- BBC NewsWorld
image source, Ella Maru Studio /Courtesy of E.Ibarra/Rice Univ.
An artist’s interpretation of the complex magnetic correlations observed by the scientists in their groundbreaking experiment. The different colors represent the six possible internal states of the ytterbium atoms.
What is the lowest temperature you can imagine? The lowest measured on Earth is -89.2 ℃ in Antarctica. In some places on the Moon it can drop below -200℃.
But an international team of scientists reached an even lower temperature, the lowest ever recorded in the universe.
Researchers at Rice University, in the United States, and Kyoto University, in Japan, obtained a temperature in the laboratory 3 billion times colder than interstellar space.
The scientists used laser beams to cool atoms to a temperature just one billionth of a degree above minus 273.15℃, absolute zero on the Kelvin scale. This is the temperature at which all motion of the atoms completely stops.
The experiment is not only a great achievement at the laboratory level. Also “opens the doors to the development of new materials with unimaginable propertiesFrancisco José Torcal-Milla, a professor in the Department of Applied Physics at the University of Zaragoza, told BBC Mundo.
For example, at temperatures close to absolute zero, helium becomes “superfluid, a state characterized by the total absence of viscosity. This means that it can pass through walls and any type of material, porous or not, and against the walls of the containers that contain it,” the Spanish expert added.
One of the authors of the experiment and the study that describes it is Mexican atomic physicist Eduardo Ibarra García Padilla, who is now a postdoctoral researcher at the University of California Davis after completing his PhD at Rice University.
Ibarra explained to BBC Mundo that there are phases of matter that are only accessible at the lowest temperatures.
And by accessing those temperatures and those phases, we can better understand physics problems, such as “superconductivity in copper oxides, which will have important technological applications”.
image source, Jeff Fitlow/Rice University
Mexican physicist Eduardo Ibarra García Padilla (left), with his Rice University colleagues Kaden Hazzard (center) and Hao-Tian Wei.
How was the experiment conducted?
Researchers from the United States and Japan lowered the temperature to extreme levels of ytterbium atoms, a rare earth chemical element on the periodic table with the symbol Yb.
To achieve this, they used “cooling techniques with lasers and evaporative coolingexplained Ibarra.
“Evaporative cooling It’s like having a really hot soup. What one does is blow on the soup; by doing that you remove the hottest particles and thus cool the soup,’ says the Mexican physicist.
“Experiments do the same: you play with the light that traps the atoms and you remove the hottest atoms and cool down the system.”
What are those light traps?
Torcal-Milla, that one Article revealing about the experiment, BBC told Mundo that the procedure is surrounded by the highest technology.
“It starts by sublimating (converting directly from solid to gas without going through the liquid state) ytterbium atoms. This procedure is usually done by shining a high-powered laser on a block of solid ytterbium, which vaporizes a small amount of the ytterbium. the same”.
“Once the diluted gas is obtained, it is stored in a chamber where an extreme vacuum has been created and atoms are caught by optical traps, which are like ribbons of light“.
“Then laser beams strike them from different directions. The photons from the laser, when interacting with the gas atoms, which are in motion, slow them down, decreasing their average speed and, as a result, their temperature. ”
image source, Courtesy of F. Torcal-Milla
Francisco Torcal-Milla: the experiment “opens the doors to the development of new materials with unimaginable properties”.
Where was the experiment done?
The laboratory where the record temperature was reached is located at Kyoto University. The group led by Yoshiro Takahashi and Shintaro Taie worked there.
“We provide the theoretical and numerical part of the study, which allows us to extract the temperatures at which the experiments were performed,” said Ibarra.
One of the sites most famous for its low temperature testing is the Cold Atom Laboratory, CAL, on the International Space Station.
CAL has the advantage of weightlessness, although Ibarra pointed out that weightlessness was not necessary for the studies performed on this occasion.
Torcal Milla believes it would be interesting to conduct these experiments aboard the International Space Station, “because while the gravitational interaction that individual atoms undergo due to the Earth is miniscule, it becomes more important as the other interactions are smaller. .”.
image source, POT
The Cold Atom Laboratory on the International Space Station has the advantage of zero gravity.
How does the behavior of matter change?
Ibarra explained that “there are two kinds of particles in nature, bosons (like the photons of a laser) and fermions (like the electrons in a solid), which behave differently at very low temperatures.”
The scientists used an isotope of ytterbium called 173Yb, which is a fermion.
At temperatures as low as the one reached in the experiment, matter behaves in an extraordinary way.
Torcal-Milla explained that in the case of bosons, they all fall to a minimum energy state, called the ground state, in which they become indistinguishable, called Bose-Einstein condensate.
If, on the other hand, they are fermions (fundamental particles that make up matter), they become what is known as a fermi gas or liquid, capable of climbing or even crossing walls.
The best known examples of strange behavior at low temperatures are superconductivity and superfluidity. Superconductivity occurs when a substance can transfer electricity without resistance.
On the other hand, superfluidity consists of the total loss of viscosity of a substance. This state of matter can be achieved by a Fermi fluid at extremely low temperatures, very close to absolute zero.
At these temperatures, almost everything freezes, except for some helium isotopes, which become superfluid. In this state, the liquid can climb the walls of the container in which it is contained.
image source, Getty Images
Superconducting materials can be used in levitating trains.
What future applications might this type of experiment have?
Ibarra pointed out to BBC Mundo that as we reach lower temperatures, different exotic phases of matter will appear. These can have completely different magnetic or transport properties than other materials.
In the case of a future superconductivity of, for example, copper oxides, a possible application, according to the Mexican expert, is the proposal of use superconductors to levitate trains.
“An example would be maglev trains. But I think they’ll probably be useful for other applications because it’s about being able to have electrical power with no losses.”
For Torcal-Milla, “Any experiment that advances knowledge is important, no matter how small the progress. If we could tell our grandparents that with a little device that I carry in my pocket, I can access all the information I need and also can speak and even immediately see a person who is in the antipodes, they would treat us as mad or charlatans”.
“Some discoveries have to wait to be applied and that may be the case, but there is no doubt that they will reveal to us new physics, which we cannot even foreseeadded the Spanish expert to BBC Mundo.
“Who knows if the study of these systems could reveal new physics that will lead us to the final theory that unites all fundamental forces, or reveals properties of matter at microscopic levels, still unknown.”
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