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Emergent s -Wave Interactions between Identical Fermions in Quasi-One-Dimensional Geometries

Fermions sharing orbital excitation in a Bell-singlet are found to scatter with even exchange symmetry. This new collisional mode is enabled by a non-equilibrium occupation of the excited transverse state, which was at first unintentional -- a fortuitous impurity -- and later controlled in our experimental protocol. This finding points to new combinations of dimensionality and scattering symmetry.

Publication Date: April 25, 2023

Authors: Kenneth G. Jackson, Colin J. Dale, Jeff Maki, Kevin G. S. Xie, Ben A. Olsen, Denise J. M. Ahmed-Braun, Shizhong Zhang, and Joseph H. Thywissen (CQIQC Member).


Orbital degrees of freedom play an essential role in metals, semiconductors, and strongly confined electronic systems. Experiments with ultracold atoms have used highly anisotropic confinement to explore low-dimensional physics, but they typically eliminate orbital degrees of freedom by preparing atoms in the motional ground states of the strongly confined directions. Here, we prepare multiband systems of spin-polarized fermionic potassium (40K) in the quasi-one-dimensional (q1D) regime and quantify the strength of atom-atom correlations using radio-frequency spectroscopy. The activation of orbital degrees of freedom leads to a new phenomenon: a low-energy scattering channel that has even particle-exchange parity along the q1D axis, as if the underlying interactions were s-wave. This emergent exchange symmetry is enabled by orbital singlet wave functions in the strongly confined directions, which also confer high-momentum components to low-energy q1D collisions. We measure both the q1D odd-wave and even-wave “contact” parameters for the first time and compare them to theoretical predictions of one-dimensional many-body models. The strength and spatial symmetry of interactions are tuned by a p-wave Feshbach resonance and by transverse confinement strength. Near resonance, the even-wave contact approaches its theoretical unitary value, whereas the maximum observed odd-wave contact remains several orders of magnitude below its unitary limit. Low-energy scattering channels of multi-orbital systems, such as those found here, may provide new routes for the exploration of universal many-body phenomena.

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