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Title: Can directly laser-cooled molecules reach quantum degeneracy?
Plain: So far every ultracold molecular quantum gas was made by gluing together ultracold atoms. Molecules cooled directly with lasers, which include species useful for precision measurements, have not yet been cooled far enough to behave as a single quantum wave.
Precise: Directly laser-cooled molecules (CaF, SrF, YO, CaOH and similar) in optical traps or tweezer-loaded traps. Reach phase-space density $n \lambda_{\mathrm{dB}}^3 \ge 1$ ($\lambda_{\mathrm{dB}}$ the thermal de Broglie wavelength) by evaporative, sympathetic or collisional cooling, which requires a large ratio of elastic to inelastic collisions, for example through microwave or optical shielding. Answer: observation of a Bose-Einstein condensate or degenerate Fermi gas of a laser-cooled species, or a measured collisional obstruction.
Settled by: Bimodal momentum distributions (bosons) or Fermi-surface signatures (fermions) in a gas of directly laser-cooled molecules.
Kind: well-posed
Answer type: yes-no
References: (empty)
Literature status: open
Status note: Blue-detuned magneto-optical traps raised the densities of laser-cooled YO and CaF (Burau et al., PRL 2023; Li et al., PRL 2024), but reported phase-space densities remain far below 1, and a 2025 perspective still describes condensation as a goal (Zeng et al., Quantum Review Letters 2025).
Posed since: (empty)