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Seminarium Optyczne

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Zapraszamy do sali 0.06, ul. Pasteura 5 o godzinie 10:15

Tomasz Sowiński (Institute of Physics, Polish Academy of Sciences)

Many-Body Correlations in Mesoscopic Multi-Component Fermionic Systems

One of the most remarkable manifestations of many-body physics is the collective emergence of quantum effects in the macroscopic world. The existence of phenomena such as superfluidity, superconductivity, giant magnetoresistance, or Bose–Einstein condensation relies directly on the macroscopic amplification of quantum properties, which are driven by mutual interactions and quantum statistics when the number of particles becomes sufficiently large. In order to better understand how this quantum collectivism emerges, it is worth considering strongly correlated quantum systems containing a small number of particles and searching for various precursors of macroscopic correlations. This approach has become particularly attractive in recent years due to the development of extremely precise experimental techniques that allow for the preparation and control of systems containing a small number of strongly interacting ultracold atoms. In my talk, I will first provide a brief review of recent progress in theoretical and experimental studies of mesoscopic ultracold systems, focusing primarily on two-component fermionic mixtures. In particular, I will explain how precursors of conventional Bardeen–Cooper–Schrieffer (BCS) and unconventional Fulde–Ferrell–Larkin–Ovchinnikov (FFLO) pairing can be identified in mesoscopic systems. Next, I will present the first results for the simplest three-component fermionic mixtures, highlighting the existence of a surprising structural transition in the many-body ground state that has no counterpart in two-component systems.

Zapraszamy do sali 0.06, ul. Pasteura 5 o godzinie 10:15

Jacek Gębala (Faculty of Physics, University of Warsaw)

Universality in Ionic Three-body Systems Near an Ion-atom Feshbach Resonance

We calculate bound and scattering properties of a system of two neutral atoms and an ion near an atom-ion Feshbach resonance. Our results indicate that long-range atom-ion interactions lead to significant deviations from universal behavior derived from contact or van der Waals potentials. We find that ionic systems display an overall suppression of inelastic transitions leading to recombination rates and lifetimes of Efimov state orders of magnitude smaller with respect to those for neutral atoms. We further characterize the dense spectra of triatomic molecular ions with extended lifetimes. Our results provide a deeper insight on the universality and structure of three-body ionic systems and establishing them as a promising platform for exploring novel few- and many-body phenomena with long-range interactions.

Zapraszamy do sali 0.06, ul. Pasteura 5 o godzinie 10:15

Kang-Da Wu (University of Science and Technology of China, Hefei)

Nonlinear Non-Hermitian Physics in Dissipative Rydberg Gases：Liouville exceptional structure and stochastic resonance

This study explores the nonlinear non-Hermitian physics in dissipative Rydberg gases, focusing on Liouvillian exceptional structures and stochastic resonance for sensing applications. Using a thermal Rydberg vapor as a many-body open system, we experimentally demonstrate chiral switching between two collective steady states with distinct excitation and transmission properties. This dynamics is governed by a Liouvillian exceptional structure, where two exceptional lines merge at a higher-order exceptional point, underpinning both the bistability and the chirality of the state transfer under parameter modulation. Such a non-Hermitian perspective offers a paradigm for controlling many-body states via exceptional points. Furthermore, leveraging the strong nonlinearity and intrinsic noise in the Rydberg ensemble, we implement stochastic resonance to detect weak microwave fields. By harnessing noise, the sensor achieves a significant signal-to-noise ratio enhancement, surpassing heterodyne atomic detection sensitivity by 6.6 dB. These findings establish dissipative Rydberg gases as a versatile platform for investigating non-Hermitian physics and advancing noise-enhanced quantum sensing technologies.

Zapraszamy do sali 0.06, ul. Pasteura 5 o godzinie 10:15

Szymon Pustelny (Jagiellonian University)

Non-Hermitian Dynamics and Exceptional-Point Sensing in a Hybrid Spin System

Incorporating non-Hermitian dynamics into quantum systems leads to a range of intriguing phenomena, including non-reciprocity, parity–time symmetry breaking, and the emergence of exceptional points, at which two or more eigenstates coalesce. These features can result in enhanced sensitivity to weak perturbations, offering a distinct approach to quantum sensing.During the talk, I will discuss the emergence of exceptional points in a hybrid system composed of two distinct gases—rubidium vapor and a noble gas—and demonstrate how this framework enhances sensitivity to magnetic fields. I will also show how such a system can be employed to search for non-magnetic interactions.

Zapraszamy do sali 0.06, ul. Pasteura 5 o godzinie 10:15

Krzysztof Jachymski (Faculty of Physics, University of Warsaw)

Stone skipping with ions in degenerate quantum gases

The dynamics of a charged impurity immersed in a quantum medium can be quite complex due to the long-range nature of the interactions. The ion can excite the gas during its motion, changing momentum in a nonlinear way. I will describe the simplest theoretical approaches to this problem based on the transformation to the co-moving frame. Dressing the impurity with the host atoms can result in formation of a polaronic state characterized by effective mass, which may be detectable in state-of-the art experiments. I will also report on recent experimental efforts aiming to understand three-body recombination involving an ion, which is competing with many-body effects.

Zapraszamy do sali 0.06, ul. Pasteura 5 o godzinie 10:15

Kazimierz Rzążewski (Center of Theoretical Physics, Polish Academy of Sciences)

BEC 30 (100) years later

I will review most important experiments on Bose-Einstein condensate. Squeezed among them I will also include a few remarks about our own contributions.

Zapraszamy do sali 0.06, ul. Pasteura 5 o godzinie 10:15

Michał Suchorowski (Faculty of Physics, University of Warsaw)

From Scale Invariance to Universal Droplets: A Framework for 2D Attractive Bose Gases

Ultracold two-dimensional (2D) Bose gases exhibit behaviour that differs markedly from their three-dimensional counterparts, making them a sensitive setting for studying symmetry and interaction effects. In the idealized Gross-Pitaevskii equation (GPE), scale invariance gives rise to unique phenomena such as Townes solitons, ‘strong’ self-similar collapse, and interaction-independent breathing-mode frequencies in tightly trapped systems. However, realistic bosonic systems exhibit a strong quantum anomaly, namely, a breaking of scale invariance and, in consequence, the formation of universal droplets. It remains unclear whether a simple, unified theoretical framework exists to analyse these phenomena. To address that, we introduce a density-dependent coupling into the GPE, which successfully describes this behaviour, while preserving a structure suitable for intuitive analytical and numerical exploration.In this talk, I will discuss the unique properties of ultracold low-dimensional Bose gases, with a focus on the 2D attractive Bose gas. I will show our limitations in the mathematical description of those systems and how we can overcome them with the recently introduced generalized GPE. The talk will address new experimental opportunities and theoretical challenges.

Zapraszamy do sali 0.06, ul. Pasteura 5 o godzinie 10:15

Alessio Ciamei (European Laboratory for Non-Linear Spectroscopy - LENS, Florence)

Ultracold molecules beyond the bi-alkali paradigm: from quantum chemistry to new physics searches

Despite tremendous progress in direct laser cooling of molecules, the only strategy so far able to deliver molecular gases at high phase-space density relies on the assembly from pre-cooled atoms in a two-step process: atom pairs are first converted into weakly bound molecules across a Feshbach resonance and later transferred to the absolute molecular ground state via stimulated Raman adiabatic passage. However, this method has so far been experimentally demonstrated only for bi-alkali systems with singlet electronic ground states.In my talk, I will initially review our results, in collaboration with M. Tomza’s group (UWarsaw), on the association of alkali lithium and transition-metal chromium into polar paramagnetic molecules [1], and preliminary benchmarks of quantum chemistry methods on Cr-bearing diatomics. I will then focus on our recent joint proposal [2] for next-generation searches for new physics based on high-spin, Σ-state, polar molecules in the ultracold regime. I will explain how these can be realized by assembly of chromium and ytterbium atoms into YbCr and describe their favorable properties from the experimental point of view. [1] S. Finelli et al., PRX Quantum 5, 020358 (2024)[2] A. Ciamei et al., arXiv:2507.16760

Despite tremendous progress in direct laser cooling of molecules, the only strategy so far able to deliver molecular gases at high phase-space density relies on the assembly from pre-cooled atoms in a two-step process: atom pairs are first converted into weakly bound molecules across a Feshbach resonance and later transferred to the absolute molecular ground state via stimulated Raman adiabatic passage. However, this method has so far been experimentally demonstrated only for bi-alkali systems with singlet electronic ground states.In my talk, I will initially review our results, in collaboration with M. Tomza’s group (UWarsaw), on the association of alkali lithium and transition-metal chromium into polar paramagnetic molecules [1], and preliminary benchmarks of quantum chemistry methods on Cr-bearing diatomics. I will then focus on our recent joint proposal [2] for next-generation searches for new physics based on high-spin, Σ-state, polar molecules in the ultracold regime. I will explain how these can be realized by assembly of chromium and ytterbium atoms into YbCr and describe their favorable properties from the experimental point of view.[1] S. Finelli et al., PRX Quantum 5, 020358 (2024)[2] A. Ciamei et al., arXiv:2507.16760

Zapraszamy do sali 0.06, ul. Pasteura 5 o godzinie 10:15

Sebastian Blatt (planQC, Garching, Germany)

Neutral-atom quantum computing in the Munich Quantum Valley

Analog quantum simulators based on ultracold atoms trapped in optical lattices can be used to study condensed matter systems with single-site resolution. The quest for more control over individual atoms in such systems has culminated in a new generation of experiments based on atom arrays assembled with optical tweezers. These atom arrays can be created rapidly in arbitrary two- and three-dimensional geometries, and atoms in these arrays can be entangled using long-range Rydberg interactions. Based on these developments, atom arrays have emerged as one of the most promising platforms to build digital quantum computers, because (1) atoms can realize qubits with many seconds of coherence time; (2) they have no manufacturing variations; and (3) it is easy to scale up to arrays with thousands of qubits. Here, I report on the digital quantum computer demonstrators developed in the academic projects within the Munich Quantum Valley and the commercial quantum computers developed at our spin-off, planqc.

Zapraszamy do sali 0.06, ul. Pasteura 5 o godzinie 10:15

Sid Wright (Fritz Haber Institute of the Max Planck Society, Berlin)

Aluminum monofluoride: Three MOTs, and a molecule that bounces off surfaces

Aluminum monofluoride (AlF) is the first spin-singlet molecule to be laser-cooled and captured into a magneto-optical trap (MOT). Its electronic structure is distinct from other laser-cooled molecules, and results in several highly attractive properties: chemical and collisional stability; efficient gas-phase molecular production via a thermochemical reaction; simple optical cycling in any excited rotational level; and a narrow, spin-forbidden, vibrationally diagonal transition from the ground state.In this talk, I will present the latest results from the AlF group in Berlin, where we have now demonstrated a MOT for three different rotational levels of the electronic ground state. I will discuss the experimental challenges and improvements to be made, the prospect of trapping higher rotational levels, and some future plans. Recently, we discovered that AlF can survive collisions with (and therefore thermalise to) room temperature surfaces, despite it having a negligible equilibrium vapour pressure below about 500 K. I will present our first velocity- and angle-resolved measurements of single AlF-surface collision outcomes observed via laser-induced-fluorescence on a camera. We tentatively find that, as shown recently for atomic Yb and Fe, specific polymer-coated surfaces lead to very low sticking probability for AlF. This opens up prospects for cheap, compact and cryogen-free molecular sources for future experiments.

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