arXiv subjects

Manuel Jäger

Publications and source records attributed to Manuel Jäger.

4 recordsLinked to original sources

arXiv2023

Holographic imaging of an array of submicron light scatterers at low photon numbers

We experimentally test a recently proposed holographic method for imaging coherent light scatterers which are distributed over a 2-dimensional grid. In our setup the scatterers consist of a back-illuminated, opaque mask with submicron-sized holes. We study how the imaging fidelity depends on various parameters of the set-up. We observe that a few hundred scattered photons per hole already suffice to obtain a fidelity of 96% to correctly determine whether a hole is located at a given grid point. The holographic method demonstrated here has a high potential for applications with ultracold atoms in optical lattices.

cond-mat.quant-gas↗

arXiv2023

Precise photoexcitation measurement of Tan's contact in the entire BCS-BEC crossover

We study two-body correlations in a spin-balanced ultracold harmonically trapped Fermi gas of $^6$Li atoms in the crossover from the Bardeen-Cooper-Schrieffer (BCS) to the Bose-Einstein-Condensate (BEC) regime. For this, we precisely measure Tan's contact using a novel method based on photoexcitation of atomic pairs, which was recently proposed by Wang et al. [Phys. Rev. A 104 063309 (2021)]. We map out the contact in the entire phase diagram of the BCS-BEC crossover for various temperatures and interaction strengths, probing regions in phase-space that have not been investigated yet. Our measurements reach an uncertainty of $\approx 2 \%$ and thus represent a precise quantitative benchmark. We compare our data to theoretical predictions and interpolations and localize the regions in phase space where the latter give valid results. In regions where the contact is already well known we find excellent agreement with our measurements. Thus, our results demonstrate that photoinduced loss is a precise probe to measure quantum correlations in a strongly interacting Fermi gas.

cond-mat.quant-gas↗

arXiv2020

Second sound in the BEC-BCS crossover

Second sound is an entropy wave which propagates in the superfluid component of a quantum liquid. Because it is an entropy wave, it probes the thermodynamic properties of the quantum liquid which are determined, e.g., by the interaction strength between the particles of the quantum liquid and their temperature. Here, we study second sound propagation for a large range of interaction strengths within the crossover between a Bose-Einstein condensate (BEC) and the Bardeen-Cooper-Schrieffer (BCS) superfluid. In particular, we investigate the strongly-interacting regime where currently theoretical predictions only exist in terms of an interpolation between the BEC, BCS and unitary regimes. Working with a quantum gas of ultracold fermionic $^6$Li atoms with tunable interactions, we show that the second sound speed varies only slightly in the crossover regime. We gain deeper insights into sound propagation and excitation of second sound by varying the excitation procedure which ranges from a sudden force pulse to a gentle heating pulse at the cloud center. These measurements are accompanied by classical-field simulations which help with the interpretation of the experimental data. Furthermore, we determine the spatial extension of the superfluid phase and estimate the superfluid density. In the future, this may be used to construct the so far unknown equation of state throughout the crossover.

cond-mat.quant-gas↗

arXiv2019

Pair fraction in a finite temperature Fermi gas on the BEC side of the BCS-BEC crossover

We investigate pairing in a strongly interacting two-component Fermi gas with positive scattering length. In this regime, pairing occurs at temperatures above the superfluid critical temperature; unbound fermions and pairs coexist in thermal equilibrium. Measuring the total number of these fermion pairs in the gas we systematically investigate the phases in the sectors of pseudogap and preformed-pair. Our measurements quantitatively test predictions from two theoretical models. Interestingly, we find that already a model based on classical atom-molecule equilibrium describes our data quite well.

cond-mat.quant-gas↗