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Universal Borromean Binding in Spin-Orbit-Coupled Ultracold Fermi Gases

Xiaoling Cui and Wei Yi
Phys. Rev. X 4, 031026 – Published 13 August 2014
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Abstract

Borromean rings and Borromean binding, a class of intriguing phenomena as three objects are linked (bound) together while any two of them are unlinked (unbound), widely exist in nature and have been found in systems of biology, chemistry, and physics. Previous studies have suggested that the occurrence of such a binding in physical systems typically relies on the microscopic details of pairwise interaction potentials at short range and is, therefore, nonuniversal. Here, we report a new type of Borromean binding in ultracold Fermi gases with Rashba spin-orbit coupling, which is universal against short-range interaction details, with its binding energy only dependent on the s-wave scattering length and the spin-orbit-coupling strength. We show that the occurrence of this universal Borromean binding is facilitated by the symmetry of the single-particle dispersion under spin-orbit coupling and is, therefore, symmetry selective rather than interaction selective. The state is robust over a wide range of mass ratios between composing fermions, which are accessible by Li-Li, K-K, and K-Li mixtures in cold-atom experiments. Our results reveal the importance of single- particle spectral symmetry in few-body physics and shed light on the emergence of new quantum phases in a many-body system with exotic few-body correlations.

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  • Received 31 March 2014

DOI:https://doi.org/10.1103/PhysRevX.4.031026

This article is available under the terms of the Creative Commons Attribution 3.0 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

Synopsis

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Knots for All Occasions

Published 13 August 2014

A universal mechanism for the formation of Borromean rings has been revealed in cold gases of fermions.

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Authors & Affiliations

Xiaoling Cui1,* and Wei Yi2,3,†

  • 1Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, People’s Republic of China
  • 2Key Laboratory of Quantum Information, University of Science and Technology of China, CAS, Hefei, Anhui 230026, People’s Republic of China
  • 3Synergetic Innovation Center of Quantum Information and Quantum Physics, University of Science and Technology of China, Hefei, Anhui 230026, People’s Republic of China

  • *xlcui@iphy.ac.cn
  • wyiz@ustc.edu.cn

Popular Summary

Borromean binding and Borromean rings belong to a class of intriguing phenomena in which three objects bound together can all be freed by removing just one object. Because of their peculiarity, these phenomena have attracted considerable attention in different contexts, and observations of Borromean binding in chemical, biological, and physical systems have generated much excitement. Previous studies of Borromean states in physical systems typically depend on short-range details of the interaction potentials, rendering the results nonuniversal. The nonuniversality makes a unified understanding of Borromean binding conceptually difficult and renders its experimental detection inconveniently system dependent. We reveal, for the first time, the existence of universal Borromean binding in ultracold Fermi gases with synthetic spin-orbit coupling.

The properties of Borromean bindings in our system are only characterized by a limited number of system-independent parameters, regardless of any underlying microscopic details of short-range interaction potentials. Furthermore, the bindings that we find are insensitive to changes in the spin dependence of the atomic interactions. Such universal properties are facilitated by the single-particle spectral symmetry under spin-orbit coupling, and therefore, they are exceedingly robust over a wide parameter regime in cold-atom experiments. We show, for the first time, using potassium and lithium gases, that universality, a central concept in physics used to explain and predict many-body collective phenomena, can also be established for intricate and peculiar Borromean bindings.

These findings reveal the importance of single-particle spectral symmetry in few-body physics and shed light on nontrivial few-body phenomena in nuclear systems, as well as the emergence of new quantum phases in a many-body system with exotic few-body correlations.

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Vol. 4, Iss. 3 — July - September 2014

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