Optics Seminar
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2020-11-26 (Thursday)
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mgr Hubert Jóźwiak (UMK Toruń)Application of accurate molecular spectra for studying of molecular collisions and interactions
Accurate measurements of the shapes of molecular resonances provide information about moleculardynamics and validate the potential energy surfaces for various collisional systems. This is due tothe fact that the collision-perturbed velocity distribution of the optical coherence manifests itself asthe perturbation of the shape of such resonance. We present a theoretical description of this process,using state-of-the-art potential energy surfaces and quantum scattering calculations for diatom-atomand diatom-diatom systems. Not only does this approach properly describe the internal andtranslational motions of the molecules, but also correlations between them. This results in thesubpercent agreement between the calculated and measured spectral line profiles. These theoreticaldevelopments are important for reducing systematic errors in optical metrology based on molecularspectroscopy (for instance, they allow for more accurate determination of rovibrational splitting inmolecular hydrogen and, hence, for accurate tests of quantum electrodynamics for molecules).Accurate theoretical models of the collision-perturbed molecular spectra will be used for populatingline-by-line spectroscopic databases and providing reference spectra for the studies of planetaryatmospheresInstrukcja obsługi połączenia
Seminarium z użyciem połączenia internetowegohttps://zoom.us/j/97696726563(meeting ID: ID 97696726563, password: 314297)
2020-11-19 (Thursday)
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dr Krzysztof Jachymski (IFT UW)Dynamics of a charged impurity immersed in a Bose-Einstein condensate
An impurity immersed in a quantum environment can be viewed as a fundamental building blockfor many-body problems and give insight into the transport properties of different materials.Ultracold atoms provide here an excellent playground, allowing for precise control of experimentalconditions and reaching a wide regime of system parameters. An intriguing possibility is to makeuse of charged impurities such as atomic ions, which interact more strongly with the backgroundgas. In a recent experiment, a single low energy ion has been created inside a Bose-Einsteincondensate. Using a precisely tuned electric field pulse, its subsequent collisional dynamics subjectto an external force has been studied. Comparison of the measurements with stochastic trajectorysimulations based on sequential Langevin collisions indicates diffusive transport properties of theimpurity and allows to extract its mobility. In a fraction of events, molecular ion formation viathree-body recombination can occur. The experimental setup allows to study the subsequentchemical dynamics of the produced molecule, which undergoes vibrationally inelastic collisionswith the host gas.
seminarium z użyciem połączenia internetowegohttps://zoom.us/j/97696726563(meeting ID: ID 97696726563, password: 314297)
2020-11-12 (Thursday)
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dr Jan Arlt (Center for Quantum Optics and Quantum Matter Department of Physics and Astronomy Aarhus University)Fluctuations of a Quantum Gas: Solving the Ensemble Question
Quantum systems are typically characterized by the inherent fluctuation of their physical properties.The size of these fluctuations is particularly relevant for the case of interacting Bose gases at thetransition to Bose-Einstein condensation. Despite its importance this case has resisted a consistentexperimental and theoretical investigation for decades. In collaboration with the group led byKazimierz Rzążewski we have characterized these fluctuations in an experimentally accessiblerange of aspect ratios, temperatures and atom numbers. Strikingly, we observe fluctuations reducedby 27% below the canonical expectation for a non-interacting gas, revealing the microcanonicalnature of our system. Moreover, we explore the scaling of these fluctuation with atom numberproviding an exponent of 1.134 in a region outside the thermodynamic limit. Our experimentalresults thus set a benchmark for further theoretical calculations under experimental conditions.
Seminarium z użyciem połączenia internetowegohttps://zoom.us/j/97696726563(meeting ID: ID 97696726563, password: 314297)
2020-11-05 (Thursday)
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mgr Maciej Bartłomiej Kruk (IF PAN)Quantum Metropolis Algorithm for Condensate Fluctuations
For decades, the study of Bose-Einstein condensate fluctuations was exclusively in the domain oftheory. However, about two years ago, Jan Arlt's team was able to measure for the first time BECfluctuations and interpret them with the help from the CTP PAS team. Since then, newmeasurements were performed and our team was able to develop a more robust method of studyingBEC fluctuations: the quantum Metropolis algorithm. I will present this new method and ourtheoretical predictions.
seminarium z użyciem połączenia internetowegohttps://zoom.us/j/97696726563(meeting ID: ID 97696726563, password: 314297)
2020-10-29 (Thursday)
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mgr Mateusz Winkowski (IFD UW)Optical detection of cancer biomarkers in air exhaled from human lungs
Optical detectors of formaldehyde and ethane (cancer biomarkers) in air exhaled from human lungs will bepresented. Application of the sensor is also possible for free atmosphere enabling continuous assessment ofair quality.Principle of the sensor operation is based on light absorption at wavelength tuned to spectral line(fingerprint) of the compound of interest. The measurement is performed in mid infrared range. In order toachieve the best immunity against typical interferents, which might occur at high concentration in humanbreath (water vapour -5%, carbon dioxide - 5%, methane -up to 10 ppm), the pressure reduction is applied.That leads to narrowing and separation of the absorption lines of various compounds due to limitation of thecollisional broadening.Multipass absorption spectroscopy is applied. Custom made multipass cells are used in the experimentalsystem. Original method of optical interferences quenching by wavelength modulation and signal averagingwill be presented. It provides opportunity to efficiently suppress undesired fringes occurring in multipass celland to increase the sensitivity of the spectroscopic system. The approach is reproducible, does not requireany mechanical and optical elements and can be adapted to various optical systems.Application of these approaches enables to achieve the detection limit of about several ppb for bothformaldehyde and ethane. Such sensitivity is better than the morbid level of the biomarkers.
Seminarium z użyciem połączenia internetowegohttps://zoom.us/j/97696726563(meeting ID: ID 97696726563, password: 314297)
2020-10-22 (Thursday)
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mgr Mikołaj Rogóż (IFD UW)Liquid crystal elastomers in light-driven systems
Liquid crystal elastomers (LCE) are elastic polymers that can reversibly change shape underexternal stimuli. The induced deformation depends on the material’s molecular order which can beadjusted during the fabrication process. Selective activation by laser light offers building lightdrivensystems.Living creatures use many different mechanisms of locomotion. Some organisms use legs to jumpor walk, others generate waves along their bodies. I will present light-driven elastomeric robots,designed to mimic the movement mechanisms of biological organisms. Robots can move indifferent directions or even crawl up a vertical surface.Rotary movement in nature is very rare while it is the basis of human civilization. Probably one ofthe most important inventions was the rotary motor. I will introduce the new concept of elastomericrotary micro-motor powered by light.
Seminarium z użyciem połączenia internetowegohttps://zoom.us/j/97696726563(meeting ID: ID 97696726563, password: 314297)
2020-10-15 (Thursday)
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mgr Piotr Grochowski (Centrum Fizyki Teoretycznej PAN)Breathing Mode of a Bose-Einstein Condensate Immersed in a Fermi Sea
Abstract:Grochowski et al. [Phys. Rev. Lett. 125, 103401 (2020)]By analyzing the breathing mode of a Bose-Einstein condensate repulsively interacting with apolarized fermionic cloud, we further the understanding of a Bose-Fermi mixture recently realizedby Lous et al. [Phys. Rev. Lett. 120, 243403 (2018)]. We show that a hydrodynamic description of adomain wall between bosonic and fermionic atoms reproduces the experimental data of Huang et al.[Phys. Rev. A 99, 041602(R) (2019)]. Two different types of interaction renormalization areexplored, based on lowest-order constrained variational and perturbation techniques. In order toreplicate nonmonotonic behavior of the oscillation frequency observed in the experiment,temperature effects have to be included. We find that the frequency down-shift is caused by thefermion-induced compression and rethermalization of the bosonic species as the system is quenchedinto the strongly interacting regime.
Seminarium z użyciem połączenia internetowegohttps://zoom.us/j/97696726563(meeting ID: ID 97696726563, password: 314297)