Abstract
Understanding the nature of confinement, as well as its relation with the spontaneous breaking of chiral symmetry, remains one of the long-standing questions in high-energy physics. The difficulty of this task stems from the limitations of current analytical and numerical techniques to address nonperturbative phenomena in non-Abelian gauge theories. In this work, we show how similar phenomena emerge in simpler models, and how these can be further investigated using state-of-the-art cold-atom quantum simulators. More specifically, we introduce the rotor Jackiw-Rebbi model, a ()-dimensional quantum field theory where interactions between Dirac fermions are mediated by quantum rotors. Starting from a mixture of ultracold atoms in an optical lattice, we show how this quantum field theory emerges in the long-wavelength limit. For a wide and experimentally relevant parameter regime, the Dirac fermions acquire a dynamical mass via the spontaneous breakdown of chiral symmetry. We study the effect of both quantum and thermal fluctuations, and show how they lead to the phenomenon of chiral symmetry restoration. Moreover, we uncover a confinement-deconfinement quantum phase transition, where mesonlike fermions fractionalize into quarklike quasiparticles bound to topological solitons of the rotor field. The proliferation of these solitons at finite chemical potentials again serves to restore the chiral symmetry, yielding a clear analogy with the quark-gluon plasma in quantum chromodynamics, where the restored symmetry coexists with the deconfined fractional charges. Our results indicate how the interplay between these phenomena could be analyzed in more detail in realistic atomic experiments.
- Received 24 August 2020
- Accepted 20 November 2020
DOI:https://doi.org/10.1103/PRXQuantum.1.020321
Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.
Published by the American Physical Society
Physics Subject Headings (PhySH)
Popular Summary
According to the Standard Model of particle physics, quarks are in general confined together forming more complicated objects, such as protons and neutrons. However, in extreme circumstances, such as at the dense core of neutron stars or at the extremely high temperatures that took place after the Big Bang, they become deconfined and independent, forming a so-called quark-gluon plasma. Understanding the nature of this confinement-deconfinement phase transition is still an open problem in high-energy physics, stemming from the complexity of solving the corresponding non-Abelian gauge theories describing such nonperturbative processes using standard analytical or numerical techniques. Quantum simulators can approach this and related questions in a more efficient manner and, in this work, we show how to do so in simplified cases using cold-atomic systems.
In particular, we show how a Bose-Fermi atomic mixture in an optical lattice can be described at low energies by a quantum field theory that, although much simpler, shares many qualitative features with quantum chromodynamics, the sector of the Standard Model describing quarks. We find a confinement-deconfinement transition between fractionally charged quasiparticles, and show how it could be investigated using state-of-the-art experimental resources. Other similarities with quark physics include dynamical mass generation and chiral symmetry restoration. Despite the microscopic differences, such a near-term simulator can help us understand universal features about confinement that could foster further progress in particle physics.
This work thus suggests alternative paths to study high-energy phenomena where, instead of simulating the full problem at hand, the flexibility of atomic systems is employed to design simplified models where the former also emerge.
