Welcome to the ultracold quantum gas research group at Aarhus University!
In our research we investigate the properties of atomic gases at extremely low temperatures. This allows us to get fundamental knowledge of quantum mechanical behaviour in few- and many-particle systems.
In October, Andreas successfully defended his PhD titled "Observation of quantum beats and induced interactions - Polarons in Bose-Einstein condensates".
The assessment committee consisted of Prof. Jacques Tempere from the University of Antwerp and Assoc. Prof. Robert Smith from the University of Oxford
Andreas will stay in the group as a postdoc to continue with his scientifc work!
His thesis is available here.
(10/2024)
In a recent paper we presented our investigations of atom number fluctuations in a partially condensed Bose gas. A microcanonical approach allows for analyzing both the thermal and condensed components resulting in a comprehensive analysis for the atom number uncertainties. Importantly, this analysis allows for estimating the BEC atom number fluctuation close to the critical temperature, which is observed to be 41% lower compared to previous analysis. Finally, by simulating known noise contributions through Monte-Carlo simulations, the technical noise contributions of the experiment are estimated, a technique which can be generally applied in our field.
Our paper is available here.
(09/2024)
In a recent paper we presented a calibration technique for analyzing absorption images, which addresses the ubiquitous problem of accurately determining atom numbers in ultracold gases. The calibration coefficient shows a dependency on the optical density which varies spatially, and we provide a practical guide to account for this. Corrections in the detected atom number using this technique is demonstrated to be as high as 12% compared to previous techniques. Further work to better understand the internal scattering process of ultracold gases is necessary to include such effects in the atom number determination.
Our paper is available here.
(06/2024)
In March, Toke successfully defended his PhD titled "Statistical analysis of atom number fluctuations in quantum degenerate Bose gases".
This also marks his depature from the group as he has accepted a position at Terma!
We wish him the best of luck!
His thesis is available here.
(03/2024)
In Feburary Morten Teglgaard Strøe and Ilja Zebergs joined our group as PhD students!
Morten has joined the "MIX" lab to continue the ongoing investigations of the Bose polaron, whereas Ilja has joined the "Lattice" lab to work on EIT experiments.
CONGRATULATIONS on starting the PhD!
(02/2024)
Our work on the repulsive polaron is available on arxiv.
We have investigated the challenging many-body problem of impurities in a repulsive bosonic environment. Most strikingly, we observe an oscillatory signal that is consistent with a quantum beat between two co-existing coherent quasiparticle states: the attractive and repulsive polarons. The interferometric signal allows us to extract the polaron energies for a wide range of interaction strengths, and we identify several dynamical regimes towards the formation of the Bose polaron. Thus our results improve the understanding of quantum impurities interacting strongly with a bosonic environment.
Our paper is also available here.
(10/2023)
In a recent paper we have clarified a number of misconceptions regarding the effect of interactions on fluctuations. This discussion in the field is typically centered around the appropriate thermodynamic ensemble to be used for theoretical predictions and the effect of interactions on the observed fluctuations. We introduce the so-called Fock state sampling method to solve this classic problem of current experimental interest for weakly interacting gases. A suppression of the predicted peak fluctuations is observed when using a microcanonical with respect to a canonical ensemble. Moreover, interactions lead to a shift in the temperature of peak fluctuations for harmonically trapped gases. The absolute size of the fluctuations furthermore depends on the total number of atoms and the aspect ratio of the trapping potential. Due to the interplay of these effect, there is no universal suppression or enhancement of fluctuations.
Our paper is available here.
(03/2023)
In the spring Laurits Nikolaj Stokholm joined our group as a PhD student!
Laurits has joined the "Lattice" lab where his project aims at investigating impurities coupled to light.
CONGRATULATIONS on starting the PhD!
(03/2023)
We are part of the Center for Complex Quantum Systems (CCQ).
We are supported by the Novo Nordisk Foundation within the NERD program.
We are supported by the Independent Research Fund Denmark within the Natural Sciences subject area.
The Carlsberg foundation.
