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1. Universal density shift coefficients for the thermal conductivity and shear viscosity of a unitary Fermi gas

   https://doi.org/10.1103/PhysRevResearch.6.L042021  

   Li, Xiang; Huang, J; Thomas, J E (October 2024, Physical Review Research)

   We measure universal temperature-independent density shifts for the thermal conductivity ${\kappa }_T$and shear viscosity $\eta$, relative to the high temperature limits, for a normal phase unitary Fermi gas confined in a box potential. We show that a time-dependent kinetic theory model enables extraction of the hydrodynamic transport times ${\tau }_{\eta }$and ${\tau }_{\kappa }$from the time-dependent free decay of a spatially periodic density perturbation, yielding the static transport properties and density shifts, corrected for finite relaxation times. Published by the American Physical Society2024 

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2. Prospects for thermalization of microwave-shielded ultracold molecules

   https://doi.org/10.1103/PhysRevResearch.6.L022033  

   Wang, Reuben_R W; Bohn, John L (May 2024, Physical Review Research)

   Toward more efficient schemes for achieving deeply degenerate molecular Fermi gases, we study anisotropic thermalization in dilute gases of microwave shielded polar molecular fermions. For collision energies above the threshold regime, we find that thermalization is suppressed due to a strong preference for forward scattering and a reduction in total cross section with energy, significantly reducing the efficiency of evaporative cooling. We perform close-coupling calculations on the effective potential energy surface derived by Deng [] to obtain accurate two-body elastic differential cross sections across a range of collision energies. We use Gaussian process regression to obtain a global representation of the differential cross section over a wide range of collision angles and energies. The route to equilibrium is then analyzed with cross-dimensional rethermalization experiments, quantified by a measure of collisional efficiency toward achieving thermalization. Published by the American Physical Society2024 

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3. Probing molecular spectral functions and unconventional pairing using Raman spectroscopy

   https://doi.org/10.1103/PhysRevResearch.6.023239  

   Diessel, Oriana K; von_Milczewski, Jonas; Christianen, Arthur; Schmidt, Richard (June 2024, Physical review research)

   An impurity interacting with an ultracold Fermi gas can form either a polaron state or a dressed molecular state, the molaron, in which the impurity forms a bound state with one gas particle. This molaron state features rich physics, including a negative effective mass around unitarity and a first-order transition to the polaron state. However, these features have remained so far experimentally inaccessible. In this work we show theoretically how the molaron state can be directly prepared experimentally even in its excited states using Raman spectroscopy techniques. Initializing the system in the ultrastrong coupling limit, where the binding energy of the molaron is much larger than the Fermi energy, our protocol maps out the momentum-dependent spectral function of the molecule. Using a diagrammatic approach we furthermore show that the molecular spectral function serves as a direct precursor of the elusive Fulde-Ferell-Larkin-Ovchinnikov phase, which is realized for a finite density of fermionic impurity particles. Our results pave the way to a systematic understanding of how composite particles form in quantum many-body environments and provide a basis to develop new schemes for the observation of exotic phases of quantum many-body systems. Published by the American Physical Society2024 

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4. Exact thermodynamics for weakly interacting normal-phase quantum gases: Equations of state for all partial waves

   https://doi.org/10.1103/PhysRevResearch.6.033173  

   Gao, Xin-Yuan; Blume, D; Yan, Yangqian (August 2024, Physical Review Research)

   While the thermodynamics for bosonic systems with weak $s$-wave interactions has been known for decades, a general and systematic extension to higher partial waves has not yet been reported. We provide closed-form expressions for the equations of state for weakly interacting systems with arbitrary partial waves in the normal phase. Thermodynamics, including contact, loss rate, and compressibility, are derived over the entire temperature regime. Our results offer an improved thermometer for ultracold atoms and molecules with weak high-partial wave interactions. Published by the American Physical Society2024 

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5. Quasielastic lepton-nucleus scattering and the correlated Fermi gas model

   https://doi.org/10.1103/PhysRevD.111.096021  

   Bhattacharya, Bhubanjyoti; Carey, Sam; Cohen, Erez O; Paz, Gil (May 2025, Physical Review D)

   The neutrino research program in the coming decades will require improved precision. A major source of uncertainty is the interaction of neutrinos with nuclei that serve as targets for such experiments. Broadly speaking, this interaction often depends, e.g., for charge-current quasielastic scattering, on the combination of “nucleon physics,” expressed by form factors, and “nuclear physics,” expressed by a nuclear model. It is important to get a good handle on both. We present a fully analytic implementation of the correlated Fermi gas model for electron-nucleus and charge-current quasielastic neutrino-nucleus scattering. The implementation is used to compare separately form factors and nuclear model effects for both electron-carbon and neutrino-carbon scattering data. Published by the American Physical Society2025 

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