Dynamics of a quantum system reveal universal physics

New experiments using ultra-cold atoms in one dimension show that quantum systems with many particles change over time when a lot of energy is added, throwing the system out of balance. Penn State physicists demonstrated that these gases immediately responded, “evolving” with characteristics typical of all “many-body” quantum systems thrown out of balance in this manner. A paper portraying the tests appears on May 17, 2023, in the journal Nature.

David Weiss, Distinguished Professor of Physics at Penn State and one of the research team’s leaders, stated, “The behavior of quantum systems with many particles has been the focus of many major advances in physics over the last century.” Regardless of the stunning cluster of different ‘many-body’ peculiarities, similar to superconductivity, superfluidity, and attraction, it was observed that their conduct close to balance is much of the time comparative enough that they can be arranged into a little arrangement of widespread classes. On the other hand, there are few descriptions that can be used to describe the behavior of systems that are far from equilibrium.

Weiss explained that these quantum many-body systems are made up of ensembles of free-floating particles, like atoms. Quantum mechanics, the fundamental theory that describes the properties of nature at the atomic or subatomic scale, is required to describe their dynamics when they are some combination of dense and cold enough, which can vary depending on the context.

“‘Hydrodynamization’ refers to the physical procedure that takes place before hydrodynamics may be applied. The situation is highly complex, and it is not feasible to really observe hydrodynamization as it occurs in the particle accelerator experiments, despite the fact that many theories have been devised to try to comprehend hydrodynamization in these collisions. We can watch what happens during hydrodynamization using cold atoms.”

Marcos Rigol, professor of physics at Penn State and another leader of the research team.

When pairs of heavy ions collide at speeds close to the speed of light, particle accelerators frequently produce systems that are dramatically out of equilibrium. The impacts produce a plasma — made out of the subatomic particles “quarks” and “gluons”—that arises right off the bat in the crash and can be portrayed by a hydrodynamic hypothesis — like the old-style hypothesis used to depict wind streams or other moving liquids — a long time before the plasma arrives at a nearby warm balance. Be that as it may, what occurs in the amazingly brief time frame before hydrodynamic hypotheses can be utilized?

Marcos Rigol, a physics professor at Penn State and another member of the research team, said, “The physical process that occurs before hydrodynamics can be used has been called hydroodynamization.” Hydrodynamization in these collisions has been the subject of numerous theories, but because the situation is so complicated, it is not possible to actually observe it in the particle accelerator experiments. We can observe hydrodynamization through the use of cold atoms.”

In order to comprehend the system’s evolution after it is thrown out of equilibrium but before hydrodynamics can be applied, the Penn State researchers took advantage of two unique characteristics of one-dimensional gases, which are trapped and cooled to near absolute zero by lasers. The main element is exploratory. Following the influx of energy, the experiment’s interactions can be abruptly turned off at any time, allowing for direct observation and measurement of the system’s evolution. In particular, they observed how momentum distributions in one dimension changed over time following the sudden loss of energy.

According to Weiss, “ultra-cold atoms in laser-made traps enable such exquisite control and measurement that they can really shed light on many-body physics.” It is amazing that the much less energetic collisions we make in our lab exhibit the same fundamental physics as relativistic heavy ion collisions, which are some of the most energetic collisions ever made in a laboratory.”

The second characteristic is conceptual. A collection of “quasiparticles” whose mutual interactions are much simpler can be described as a collection of particles that interact with one another in a complex manner. Not at all like in many frameworks, the quasiparticle portrayal of one-layered gases is numerically careful. It is considered an extremely clear depiction of why energy is quickly reallocated across the framework after it is tossed out of harmony.

Rigol stated, “Known laws of physics, including conservation laws, in these one-dimensional gases imply that once this initial evolution plays out, a hydrodynamic description will be accurate.” The investigation shows that this happens before a nearby balance is reached. As a result, the experiment and theory together provide an excellent illustration of hydrodynamization. The fundamental concept of quasi-particles can be applied to any many-body quantum system that receives a significant amount of energy because hydrodynamization occurs so rapidly.

Notwithstanding Weiss and Rigol, the examination group at Penn State incorporates Yuan Le, Yicheng Zhang, and Sarang Gopalakrishnan.

More information: Yuan Le et al, Observation of hydrodynamization and local prethermalization in 1D Bose gases, Nature (2023). DOI: 10.1038/s41586-023-05979-9

Topic : Article