26th Australian Institute of Physics Congress and the Australian and New Zealand Conference on Optics and Photonics

Polaron to clock shift: Spectroscopy of an impurity immersed in a Bose gas across the condensation threshold

Not scheduled

20m

Belinda Hutchinson Building (The University of Sydney )

Poster AIP | Quantum Science and Technology (QST)

Description

Recent fundamental spectroscopic measurements of strongly interacting impurities immersed in a thermal Bose gas (Etrych et al., 2025) have raised an intriguing, yet foundational question: what constitutes a polaron? To answer this, we theoretically investigate the impurity spectral response in a two-component thermal Bose gas across the entire phase diagram, from a Bose-Einstein condensate to well above the critical temperature.

Using a ladder approximation, we establish a direct connection between clock-shift spectroscopy and Bose polaron physics. Critically, the clock-shift protocol reduces exactly to that of an ideal Bose polaron at zero temperature, while above the critical temperature, the spectral shift is twice the polaron energy. Between these limits, we find a crossover regime driven by the simultaneous interplay of the impurity with both the condensate and the thermal cloud.

Reference:
Etrych, J., Morris, S. J., Fischer, S. M., et al. (2025). Fate of an impurity strongly interacting with a thermal Bose gas. arXiv. https://doi.org/10.48550/arxiv.2508.06493