arXiv subjects

M. T. Strøe

Publications and source records attributed to M. T. Strøe.

2 recordsLinked to original sources

arXiv2026

Observation of low-lying impurity states in Bose-Einstein condensates

Impurities embedded in a Bose-Einstein Condensate (BEC) of 39K atoms are investigated with a pump-probe ejection spectroscopy sequence. The spectroscopic signal exhibits a strong feature corresponding to a Bose polaron in agreement with prior injection spectroscopy and theory. In addition, significant spectral weight at energies well below the energy of the polaron is observed, which is absent in injection spectroscopy. The energy and spectral weight of this signal are measured as a function of interaction strength and evolution time between the pump and probe pulses. We tentatively compare these results to two different theoretical models: a low-energy impurity state dressed by many bosonic excitations and a bipolaron state formed by two polarons due to attractive interactions mediated by the BEC. Such states can exist due to the large compressibility of the weakly interacting BEC. Both theories predict ejection spectra consistent with the low-energy signal, but only the bipolaron model is compatible with its spectral weight. These results indicate that lowenergy states below the usual polaron exist for strong interactions, calling for further experimental investigations

cond-mat.quant-gas↗

arXiv2025

Three-body Physics in the Impurity Limit of 39K Bose-Einstein Condensates

Loss spectroscopy is a key tool for investigating systems where important system parameters are linked to intrinsic resonant loss processes. We investigate loss processes of impurity atoms embedded in a medium of a Bose-Einstein Condensate close to a Feshbach resonance. In this case, three-body loss processes occur faster than the measurement duration, impeding a direct time-resolved measurement. Here, we discuss how an even faster two-body loss process can be used to probe the system. The time-dependent number of atoms in the medium is reconstructed from such measurements, allowing for the extraction of the three-body loss rate coefficient $L_3$ and its scaling with scattering length. Moreover, the medium atom number is reconstructed from spectroscopic loss measurements. This allows for a comparison of the medium densities based on both the extracted loss rates and the spectroscopically reconstructed atom number. Finally, the number of lost medium atoms per loss event is evaluated and found to exceed 2 at strong interactions, which is attributed to secondary collisions in the medium. These investigations establish the use of a fast loss mechanism as a new tool in the field and provide quantitative measurements of three-body losses at large interaction strengths.

cond-mat.quant-gas↗