Measuring mutual friction in superfluids: the role of initial vortex configuration fluctuations

Year: 2025

Authors: Grani N., Hernandez-Rajkov D., Fernandez M.F., Del Pace G., Roati G.

Autors Affiliation: Univ Florence, Dept Phys, I-50019 Sesto Fiorentino, Italy; Univ Florence, European Lab Nonlinear Spect LENS, I-50019 Sesto Fiorentino, Italy; CNR, Ist Nazl Ott, LENS, I-50019 Sesto Fiorentino, Italy; INFN, Sez Firenze, I-50019 Sesto Fiorentino, Italy.

Abstract: The physical origin of mutual friction in quantum fluids is deeply connected to the fundamental nature of superfluidity. It stems from the interaction between the superfluid and normal components, mediated by the dynamics of quantized vortices that induce the exchange of momentum and energy. Despite the complexity of these interactions, their essential features can be effectively described by the dissipative point vortex model—an extension of classical vortex dynamics that incorporates finite-temperature dissipation. Mutual friction is parametrized by the longitudinal (dissipative) coefficient α and the transverse (reactive) coefficient α′. Accurate measurement of these parameters provides critical insights into the microscopic mechanisms governing vortex motion and dissipation in quantum fluids, serving as a key benchmark for theoretical models. In this work, we employ the dissipative point vortex model to study how fluctuations in the initial conditions influence the inference of α and α′ from the time evolution of the vortex trajectories. Using experimentally realistic parameters, we show that fluctuations can introduce significant biases in the extracted values of the mutual friction coefficients. We compare our findings with recent experimental measurements in strongly interacting atomic superfluids. Applying this analysis to our recent experimental results allowed us to account for fluctuations in the correct determination of α and α′.

Journal/Review: EUROPEAN PHYSICAL JOURNAL-SPECIAL TOPICS

More Information: We thank the Quantum Gases group at LENS for fruitful discussions. G.R. and G.D.P. acknowledge financial support from the PNRR MUR project PE0000023-NQSTI. G.R. acknowledges funding from the Italian Ministry of University and Research under the PRIN2017 project CEnTraL and the Project CNR-FOE-LENS-2024. The authors acknowledge support from the European Union\u2014NextGenerationEU for the \u201DIntegrated Infrastructure initiative in Photonics and Quantum Sciences\u201D\u2014I-PHOQS [IR0000016, ID D2B8D520, CUP B53C22001750006]. The authors acknowledge funding from INFN through the RELAQS project. This publication has received funding under the Horizon Europe program HORIZON-CL4-2022-QUANTUM-02-SGA via project 101113690 (PASQuanS2.1) and by the European Community\u2019s Horizon 2020 research and innovation program under grant agreement 871124.
KeyWords: Dynamics; Vortices; He-4
DOI: 10.1140/epjs/s11734-025-01924-1