The discovery of a new form of matter resulting from an atomic temperature below absolute zero

By bringing a cloud of atoms to a temperature below absolute zero, known as “negative absolute,” physicists found that it appeared to present a hitherto unknown quantum state. At this temperature, atoms can be organized into specific, complex geometric patterns called “Kagome lattices.” The resulting quantum matter could be an entirely new form of matter.

In the 19th century, Lord Kelvin defined the temperature scale by saying that any substance can fall below absolute zero (0 Kelvin, or about -273.15 degrees Celsius). However, physicists later discovered that the absolute temperature of a gas is proportional to the average energy of its constituent molecules. there Absolute temperature It is the temperature measured from absolute zero, which corresponds to the state in which particles have no kinetic energy (and are therefore immobile). A higher temperature corresponds to a certain kinetic energy.

However, physicists discovered in the 1950s that this principle was not always true, especially because of the way energy is distributed between atoms. Absolute zero corresponds to the state in which particles have a minimum of entropy. For groups of atoms with positive absolute temperature, only a few of them move with high kinetic energy, while most have a low energy level.

On the other hand, this energy distribution reverses when the atoms are exposed to a negative absolute temperature. In other words, those moving with high kinetic energy become more numerous than those with less energy (maximum entropy). Thus particles at negative absolute temperatures have more energy than those at positive absolute temperatures. Ironically, the former is technically “warmer” than the latter. Combining the two will distribute energy or heat from one (completely negative) to the other (completely positive).

By exploring this strange state of particles by controlling their energy levels and quantum states, researchers at the University of Cambridge discovered that matter exhibits an unusual state. According to experts, the experiment was only possible using the principles of quantum mechanics, not the principles of thermodynamics. Their work was presented June 5, 2024, at the annual meeting of the Division of Atomic, Molecular, and Optical Physics of the American Physical Society in Fort Worth, Texas.

Similar behavior to dark energy?

As part of their experiment, the Cambridge team placed a cloud containing thousands of potassium atoms in a vacuum chamber, then exposed it to a temperature close to absolute zero. To do this, the researchers used lasers and magnetic fields. ” We use neutral atoms in optical lattices as analog quantum simulations “, they explained in their study. This made it possible, among other things, to control the quantum and energy states of atoms, so as to bring them to a negative absolute temperature.

Note that these same researchers have already conducted… expertise A bit like what happened in 2013, using an ultracold quantum gas composed of potassium atoms. Lasers and magnetic fields have made it possible to arrange individual atoms into a lattice. At positive absolute temperatures, the atoms repel each other, making the configuration unstable. On the other hand, negative absolute temperatures (caused by the tuning of the magnetic field) caused them to attract each other, making the system more stable.

” This causes atoms to suddenly switch from the most stable, lowest energy state to the highest possible energy state, before they can react “, he explained in a blog article in the magazine nature One of the study's authors, Ulrich Schneider, from the University of Cambridge. ” It's like walking through a valley and immediately finding yourself on top of a mountain “, he added. Experts concluded that this state could lead to a new form of matter.

The new experiment's protocol was improved in this direction, by encouraging atoms to arrange themselves into complex hexagonal and triangular patterns called Kagome lattices. The researchers then found that atoms could be induced to exhibit quantum states in which their energy comes from interactions with other atoms. However, surprisingly, they did not show any kinetic energy.

It is interesting to note that gas exposed to a negative absolute temperature behaves similarly to dark energy, a hypothetical force that would be responsible for, among other things, accelerating the expansion of the universe and which conflicts with gravity. In their previous experiment, Schneider and his colleagues found that atoms attracted to each other should normally be affected by gravity, but not by the stability caused by negative absolutes. As a next step, the researchers plan to further explore the precise properties of this new material.

source : American Physical Society