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Sub-Doppler Cooling, State Preparation, and Optical Trapping of a Triel Atom

Putian Li1,*, Xianquan Yu1,2,*, Seth Hew Peng Chew3, Jinchao Mo1, Tiangao Lu1, and Travis L. Nicholson1,2,3,4,5,†

  • *These authors contributed equally to this work.
  • †Contact author: travis.nicholson@duke.edu
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PRX Quantum 6, 040328 – Published 10 November, 2025

DOI: https://doi.org/10.1103/1znr-p9nv

Abstract

Ultracold gases of atoms from main group III (group 13) of the periodic table, also known as “triel elements,” have great potential for a new generation of quantum matter experiments. The first magneto-optical trap of a triel element (indium) was recently realized, but more progress is needed before a triel is ready for modern ultracold quantum science experiments in optical traps. Reaching this regime typically requires atoms that are cooled to the 10μK level or below, prepared in pure quantum states, and confined in a laser field. Here we report the achievement of all three of these milestones in atomic indium. First, we perform polarization gradient cooling of an indium gas to 15μK. Second, we spin polarize the gas into a single hyperfine sublevel of either the 5P1/2 indium ground state or the 5P3/2 metastable state. Third, we trap indium in a 1064 nm optical lattice, achieving a 3 s trap lifetime. With these results, indium is now a candidate for a next generation quantum research platform.

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Popular Summary

Each time a new class of atoms has been cooled to ultralow temperatures, this has led to impactful experiments and unexpected discoveries. Alkali atoms enabled the first Bose-Einstein condensates, alkaline-earth atoms transformed atomic clocks, and dipolar atoms revealed new states of matter. Yet an interesting part of the periodic table—the triel elements (group 13)—has remained unexplored in the ultracold regime. Unlike other atoms in ultracold physics, triel elements have anisotropic short-range interactions, which are novel to quantum science and expected to reveal entirely new phenomena.

In this work, we demonstrate the key milestones needed to establish the triel atom indium as a promising system for experiments with ultracold atoms in optical traps. We first laser cool indium to 15 µK. We then prepare the atoms in pure quantum spin states, a prerequisite for many quantum experiments. Finally, we confine them in an optical lattice, with lifetimes that allow extended coherence-time measurements. Taken together, these advances enable optical-trap-based quantum experiments with indium.

Indium offers unique quantum measurement opportunities. Its short-range anisotropic interactions are predicted to give rise to novel bulk phases, and at low magnetic fields it forms a stable F = 4 spinor gas. This would be a higher-F spinor than those realized to date to our knowledge, and it would support non-Abelian excitations. The system is also expected to enable synthetic spin-orbit coupling with strongly suppressed parasitic heating. In addition, indium combines rare features including an ultranarrow optical transition, magnetic Feshbach resonances, and anisotropic light-matter interactions.

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PRX Quantum 6, 040328– Published 10 November, 2025
  • Received 26 November 2024
  • Revised 16 April 2025
  • Accepted 16 September 2025
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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.

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