arXiv subjects

Tobias Krom

Publications and source records attributed to Tobias Krom.

4 recordsLinked to original sources

arXiv2026

Anderson orthogonality scaling in the Rabi-driven heavy Fermi polaron

The Anderson orthogonality catastrophe (AOC) is a paradigmatic many-body phenomenon in which a local perturbation induces a macroscopic response of a Fermi sea. We probe signatures of the AOC by coherently driving heavy Fermi polarons in an ultracold $^6$Li-$^{133}$Cs mixture. We observe a power-law dependence of the measured Rabi frequency on the drive strength, with exponents consistent with AOC predictions. Finite-temperature simulations quantitatively reproduce the observed scaling, indicating that AOC signatures persist beyond the idealized zero-temperature, infinite-mass limit. The damping of the Rabi oscillations provides access to polaron dephasing and reveals a nonmonotonic drive dependence, qualitatively consistent with current theories. Our results establish coherently driven impurities as a versatile probe of quantum many-body dynamics through local coherent control.

cond-mat.quant-gas↗

arXiv2026

The heavy Fermi polaron I: the Lithium-Cesium experiment

We present details of an experimental platform for studying Fermi polarons in a quantum-gas mixture. The system consists of about a thousand bosonic $^{133}$Cs impurities immersed in a deeply degenerate Fermi gas ($T/T_F \sim 0.2$) of approximately $2\times 10^5$ $^6$Li atoms in a single hyperfine state, with interspecies interactions tunable via a Feshbach resonance. Using optical Raman spectroscopy without relative momentum transfer, we perform injection spectroscopy and thereby create the Fermi polaron. Owing to the large mass imbalance between the two species, the setup provides access to previously unexplored regimes of Fermi polarons.

cond-mat.quant-gas↗

arXiv2025

Multimodal Purcell enhancement and optical coherence of Eu$^{\text{3+}}$ ions in a single nanoparticle coupled to a microcavity

Europium-doped nanocrystals constitute a promising material for a scalable future quantum computing platform. Long-lived nuclear spin states could serve as qubits addressed via coherent optical transitions. In order to realize an efficient spin-photon interface, we couple the emission from a single nanoparticle to a fiber-based microcavity under cryogenic conditions. The spatial and spectral tunability of the cavity permits us to place individual nanoparticles in the cavity, to measure the inhomogeneous linewidth of the ions, and to show a multi-modal Purcell-enhancement of two transition in Eu$^{\text{3+}}$. A halving of the free-space lifetime to 1.0 ms is observed, corresponding to a 140-fold enhancement of the respective transition. Furthermore, we observe a narrow optical linewidth of 3.3 MHz for a few-ion ensemble in the center of the inhomogeneous line. The results represent an important step towards the efficient readout of single Eu$^{\text{3+}}$ ions, a key requirement for the realization of single-ion-level quantum processing nodes in the solid state.

quant-ph↗

arXiv2024

An experimental platform for studying the heteronuclear Efimov effect with an ultracold mixture of $^6$Li and $^{133}$Cs atoms

We present the experimental apparatus enabling the observation of the heteronuclear Efimov effect in an optically trapped ultracold mixture of $^6$Li-$^{133}$Cs with high-resolution control of the interactions. A compact double-species Zeeman slower consisting of four interleaving helical coils allows for a fast-switching between two optimized configurations for either Li or Cs and provides an efficient sequential loading into their respective MOTs. By means of a bichromatic optical trapping scheme based on species-selective trapping we prepare mixtures down to 100 nK of 1$\times$ 10$^4$ Cs atoms and 7$\times$ 10$^3$ Li atoms. Highly stable magnetic fields allow high-resolution atom-loss spectroscopy and enable to resolve splitting in the loss feature of a few tens of milligauss. These features allowed for a detailed study of the Efimov effect.

cond-mat.quant-gas↗