Researchers have theoretically described a new quantum state where ultracold atoms maintain order despite high energy. The study, published in Physical Review Letters, challenges existing theories of one-dimensional quantum systems.
By Hermes-Vector AI Desk
Physicists have developed a theoretical framework for a new state of quantum matter called a "fractional Fermi sea." In this state, ultracold cesium atoms are driven into a highly excited configuration while maintaining a hidden order, defying standard expectations for systems pushed far from equilibrium.
The research was conducted by a team led by Hanns-Christoph Nägerl at the University of Innsbruck, in collaboration with theoretical physicist Alvise Bastianello of the CNRS and Université Paris-Dauphine. The study was published in Physical Review Letters.
The scientists focused on ultracold cesium atoms confined to a one-dimensional system. By repeatedly cycling the interactions between these atoms from strong repulsion to strong attraction, they observed an unexpected result. Instead of becoming disordered, the atoms rearranged themselves into a new many-body state.
"Instead of simply heating the system, the interaction cycle reorganizes the atoms into a new many-body state," said Yi Zeng, the leading author of the study. "This gives us a controlled way to explore quantum matter beyond the usual equilibrium paradigms."
The researchers named this configuration a fractional Fermi sea because the particles appear to obey a modified rule for how quantum states are occupied. Alvise Bastianello explained the premise of the experiment: "Fermions, for instance, stack neatly into the available energy states to form the so-called 'Fermi sea'. But what happens if one forces interacting atoms to continuously cycle through extreme conditions, smoothly shifting them from strongly repelling each other to strongly attracting each other?"
A key feature of the fractional Fermi sea is that it remains organized even though the system is highly excited. The researchers identified distinctive mathematical patterns, including pronounced ripples known as Friedel oscillations. These are wave-like variations associated with how quantum particles influence one another.
The team also observed unusual patterns in how correlations between particles weaken with distance, even when repulsive interactions are relatively weak. These signatures differ from predictions made by Tomonaga-Luttinger liquid theory, a long-established framework for describing interacting quantum particles in one-dimensional systems.
"This state is highly excited, but it is not random," said Hanns-Christoph Nägerl, the group leader. "It has a hidden order that becomes visible in its correlations."
The behavior of the system raises questions about the nature of the collective excitations, or quasiparticles, that emerge within it. Nägerl suggested that these unusual excitations might eventually require a new name.
"We are not yet sure how we should name these new quasiparticles. Perhaps 'super-Fermions'?" Nägerl said.
The discovery suggests that fractional Fermi seas represent an exotic critical phase of quantum matter. The findings demonstrate the growing capability of quantum simulation, a technique that uses controlled quantum systems to investigate physical behavior that is difficult to reproduce in other contexts.
According to the researchers, this approach allows scientists to move beyond recreating known models. "The discovery of fractional Fermi seas shows how far we can push quantum simulation: not only reproducing known models, but creating and probing states that go beyond established paradigms," Nägerl said.
The current publication establishes the theoretical foundation for this state. A companion study describing the experimental realization of fractional Fermi seas through quantum simulation is currently undergoing peer review.
Sources
This article was drafted with AI assistance and checked against the sources above. Company claims are reported as claims. Cover image is AI-generated.
The day's checked news, by email
One short email a day with the top stories. Free, and you can unsubscribe in one click.
Or follow for the latest news:
No comments yet. Start the discussion.
ScienceTrending
A joint expedition by Purdue University and the Archaeological Legacy Institute found no conclusive evidence that Amelia Earhart’s plane wreckage is on Nikumaroro Island. The team determined a suspected object was likely debris from trees.
Researchers at the Max Planck Institute for Radio Astronomy identified a second jet in galaxy Mrk 501, suggesting a binary black hole system that could merge within a century.