What is the lowest temperature you can imagine? The lowest recorded on Earth is -89.2℃ in Antarctica. In some places on the Moon it can drop below -200 ℃.
But an international team of scientists achieved an even lower temperature, the lowest ever measured in the universe.
Researchers from Rice University, in the United States, and Kyoto University, in Japan, obtained a temperature in the laboratory 3 billion times cooler than interstellar space.
Scientists used lasers to cool atoms to a temperature of just one billionth of a degree above -273.15℃, absolute zero on the Kelvin scale. This is the temperature at which all movement of atoms ceases completely.
The experiment is not only a great achievement at the laboratory level. Also “opens the doors to the development of new materials with unimaginable properties“Francisco José Torcal-Milla, professor at the Department of Applied Physics at the University of Zaragoza, told BBC Mundo.
At temperatures close to absolute zero, helium, for example, “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 climb the walls of containers that contain it,” added the Spanish expert.
One of the authors of the experiment and the study that describes it is the Mexican atomic physicist Eduardo Ibarra García Padilla, who after completing his doctorate at Rice University is now a postdoctoral researcher at the University of California Davis.
Ibarra explained to BBC Mundo that there are phases of matter that are only accessible at the lowest temperatures.
And accessing those temperatures and those phases will allow us to better understand problems in physics such as “superconductivity in copper oxides, which will have important technological applications”.
How was the experiment carried out?
Researchers in the United States and Japan lowered the temperature to extreme levels of atoms of ytterbium, a rare earth element that is a chemical element in the periodic table with the symbol Yb.
To achieve this, they usedcooling techniques with lasers and evaporative coolingIbarra explained.
“Evaporative Cooling it’s like when you have a very hot soup. What one does is blow on the soup; by doing that, one removes the hottest particles and in this way cools the soup,” said the Mexican physicist.
“The experiments do the same thing: one plays with the light trap where the atoms are trapped and one removes the hottest atoms and therefore cools the system.”
What are these light traps?
Torcal-Milla, who wrote a popular article about the experiment, told BBC Mundo that the procedure is surrounded by the highest technology.
“It begins by sublimating (converting directly from a solid to a gas without going through the liquid state) ytterbium atoms. This procedure is usually carried out by shining a high-power laser on a block of solid ytterbium, causing a small amount to evaporate of the same”.
“Once the diluted gas is obtained, it is kept in a chamber where an extreme vacuum has been created and atoms are trapped by optical traps, which are like a kind of loop made of light“.
“Then they are hit with laser beams from different directions. When the laser photons interact with the gas atoms, which are stirring, they slow them down, lowering their average speed and, as a consequence, their temperature.”
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 carried out,” said Ibarra.
One of the best known sites for its low temperature tests is the Cold Atom Laboratory, CAL, on the International Space Station.
CAL has the advantage of zero gravity, although Ibarra pointed out that zero gravity was not necessary for the studies conducted on this occasion.
Torcal Milla believes that it would be interesting to carry out these experiments on board the International Space Station, “because despite the fact that the gravitational interaction suffered by individual atoms due to the Earth is tiny, it becomes more important the smaller the rest of the interactions are.” “.
How does the behavior of matter change?
Ibarra explained that “in nature there are two types of particles, bosons (like photons in a laser) and fermions (like electrons in a solid), which exhibit different behaviors at very low temperatures.”
The scientists used an isotope of ytterbium called 173Yb, which is a fermion.
At temperatures as low as that 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 ascending walls or even passing through them.
The best known examples of strange behavior at low temperatures are superconductivity and superfluidity. Superconductivity occurs when a substance is capable of transmitting 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 liquid at extremely low temperatures, very close to absolute zero.
At these temperatures almost everything freezes, except for some isotopes of helium, which become superfluid. In this state, the fluid is capable of ascending the walls of the container that contains it.
What future applications could this type of experiment have?
Ibarra told 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 copper oxides, for example, a possible application according to the Mexican expert is the proposal of use superconductors for levitating trains.
“An example is maglev trains. But I think they will probably be useful for other applications since it implies being able to have an electric current without losses.”
For Torcal-Milla, “every experiment that advances knowledge is important, no matter how small the advance. If we could tell our grandparents that with a small device in my pocket I can access any information I need and also speak and even instantly seeing a person who is in the antipodes, we would be treated as crazy or charlatans”.
“Some discoveries must wait to be applied and perhaps this is the case, but there is no doubt that they will reveal to us new physics, which we cannot even foresee“, added the Spanish expert to BBC Mundo.
“Who knows if the study of these systems could reveal new physics that will lead us to the definitive theory that unifies all the fundamental forces, or reveal properties of matter at microscopic levels, still unknown.”
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