Wydział Fizyki UW > Badania > Seminaria i konwersatoria > Seminarium Optyczne

Seminarium Optyczne

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

Rafał Kasztelanic (IGF UW)

Application of machine learning techniques and neural networks in the development of nanostructured optical fibers

Optical fibers play a key role in many fields of science and technology, forming the foundation of global telecommunications systems. With the increasing requirement to adapt their properties to specific applications, various types of optical fibers have been developed – from classical fibers with step and gradient refractive index distribution through photonic crystal fibers (PCF) and antiresonant fibers (ARF), to innovative nanostructured optical fibers (nOF). The nOF technology allows the refractive index distribution to be freely shaped, opening up new possibilities in controlling light propagation that are unavailable in traditional fabrication methods such as MCVD technology. key challenge in nOF development is determining the optimal spatial distribution of the rods. By default, an nOF fiber core is composed of 5,000 to 15,000 rods, leading to an astronomical number of 2n possible distributions. Traditional optimization methods, based on searching the entire space of possible solutions, become ineffective. As a result, previous nOF designs have been based on known refractive distributions that can be quickly adapted. However, when the optimal refractive index distribution is unknown, it becomes necessary to use advanced tools. In this context, design methods supported by machine learning (ML) algorithms and neural networks (NN) are becoming increasinglymportant in exploring and optimizing the multidimensional design spacewith unprecedented efficiency. I'll present two nOF design strategies based on ML and NN that speed up the optimization process and allow the exploration of new, previously inaccessible solutions. This increases the potential of these optical fibers in applications such as spatial multiplexing (SDM). The development of such methods has the potential to revolutionize the approach to the design of optical fibers, offering tools to fine-tune their properties to meet future technology needs.

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

Kazimierz Rzążewski (CFT PAN)

The Hybrid Sampling method for the statistics of a Bose gas

While the statistical properties of an ideal Bose gas are well understood, accounting for interaction induced corrections remains a challenging and unresolved problem. We propose a fundamentally different approach: instead of calculating partition functions, we construct models of the canonical and microcanonical ensembles directly. Previously, to this end, we developed two sampling techniques—one based on the classical field approximation and the other on Fock State Sampling (FSS). Each method offers significant advantages but also suffers from critical limitations: the classical field approach is plagued by ultraviolet divergence, while FSS neglects changes to the condensate wave function. In this talk, we introduce a new Hybrid Sampling method that overcomes these issues, combining the strengths of both earlier approaches while avoiding their respective shortcomings.

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

Tomasz Antosiewicz (IGF UW)

Nanophotonics with transition metal dichalcogenide nanoparticles and metasurfaces

Transition metal dichalcogenides (TMDs) attract research interest due to their optical and excitonic properties. A large, anisotropic refractive index of many semiconducting TMDs makes them attractive for nanophotonic applications. Design of such nanostructures requires knowledge of dielectric constants, which can then be used for single particle resonators, photonic crystals, waveguides, arrays of nanoparticles as well as their inverse designs. Here, I will discuss two cases. The first is design and fabrication of efficient nonlinear TMD nanodisks based on MoS2, which provide close to four orders of magnitude enhancement of second harmonic generation. The second example realizes high-quality nanohole-based metasurfaces in an MoS2 nanofilm. Depending on the nanohole shape, the metasurfaces can be tailored to support broken in-plane symmetry, allowing for realization of quasi-bound-states-in-the-continuum.

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

Maciej Bartłomiej Kruk (IF PAN)

Quantum droplets at nonzero temperature

I'll present our findings on quasi-2D quantum droplets at nonzero temperature. We studied the thermal Penrose-Onsager mode of quantum droplets and observe the appearance of critical temperature and density for their existence. We predict reduction of droplet bulk density and excitation of a few bound modes due to thermal fluctuations.

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

Dorota Tomaszewska-Rolla (Wrocław University of Science and Technology)

Mid-infrared optical frequency comb spectroscopy using an all-silica antiresonant hollow-core fiber

Optical frequency combs can serve as a radiation source in spectroscopic measurements, providing high sensitivity, resolution, and speed. The strongest absorption lines of many molecules are in the mid-infrared spectral range (>3 μm). To increase the sensitivity of spectroscopic systems, extending the light-gas interaction path is necessary. Classically, it is realized through multipass cells or optical cavities. However, they have some disadvantages, such as difficulty aligning the light, high losses, or unwanted interference. An alternative approach is to use the so-called antiresonant hollow-core fibers (ARHCF). ARHCFs are characterized by a wide, low-loss transmission range in the mid-IR, high quality of the delivered beam, and their air core can be filled with the target gas sample, making them well-suited for laser-based gas sensing. In this presentation, I will discuss the advantages and disadvantages of antiresonant hollow-core fibers, show the possibility of measuring gases in low vacuum, and provide evidence that ARHCFs could be a promising alternative to multipass cells.

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

The seminar is cancelled

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

Bijit Mukherjee (IFT UW)

Optical excitation and stabilization of ultracold field-linked tetratomic molecules

Trapped samples of ultracold molecules often short-lived because close collisions between them result in trap loss. To mitigate such loss, shielding methods [1, 2] have been extensively developed and have recently been successfully implemented [3-5]. Shielding is achieved by external static electric fields or near-resonant microwaves. The external field responsible for shielding also allows creation of weakly bound ultracold tetratomic molecules (“tetramers”). Recently, such tetramers have been realized from pairs of ultracold alkali-metal diatoms using an external microwave field [6]. These tetramers are termed field-linked (FL) molecules as an external field is necessary to create them.

The motivation of this work is to develop a methodology to create deeper bound tetramers starting from the loosely bound FL tetramers. We envisage extending the tools for photoassociation of ultracold atoms to produce molecules in the excited electronic states, and stimulated Raman adiabatic passage (STIRAP) transfer of weakly bound diatoms to deeply bound molecules in the ground vibronic state via an excited intermediate state. We investigate similar routes of creating deeply bound tetramers starting from weakly bound states or a pair of colliding diatoms. We consider static-electric field shielded alkali diatomic molecules initially in their ground electronic X1Σ+ + X1Σ+ pair state. We identify the excited electronic manifold X1Σ+ + b3Π0 for photoassociation and an intermediate state for STIRAP transfer to deeply bound states in the X+X manifold. For this, we develop shielding methods for X+b and predict Frank-Condon factors (FCFs) between FL states of X+b and X+X. We also predict photoassociation spectra for shielded molecules to form FL tetramers in X+b manifold. We obtain favourable FCFs between ground and excited tetramer states and promising photoassociation spectra. Our theoretical results should guide future experiments for stabilizing weakly bound ultracold tetramers.

References

1. G. Wang and G. Quéméner, New J. Phys. 17, 035015 (2015).

2. T. Karman and J. M. Hutson, Phys. Rev. Lett. 121, 163401 (2018).

3. K. Matsuda et al., Science 370, 1324 (2020).

4. A. Schindewolf et al., Nature 607, 677 (2022).

5. N. Bigagli et al., Nat. Phys. 19, 1579 (2023).

6. X.-Y. Chen et al., Nature, 626, 283 (2024).

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

Mario Krenn (Max Planck Institute for the Science of Light, Erlangen, Germany)

Towards an artificial muse for new ideas in Physics

Artificial intelligence (AI) is a potentially disruptive tool for physics and science in general. One crucial question is how this technology can contribute at a conceptual level to help acquire new scientific understanding or inspire new surprising ideas. I will talk about how AI can be used as an artificial muse in physics, which suggests surprising and unconventional ideas and techniques that the human scientist can interpret, understand and generalize to its fullest potential [1]. I will focus on AI for the design of new physics experiments, in the realm of quantum-optics [2, 3] and quantum-enhanced gravitational wave detectors [4] as well as super-resolution microscopy [5]. Finally I will discuss how algorithms with access to millions of scientific papers can predict and suggest future ideas for scientists [6,7].

[1] Krenn, Pollice, Guo, Aldeghi, Cervera-Lierta, Friederich, Gomes, Häse, Jinich, Nigam, Yao, Aspuru-Guzik, On scientific understanding with artificial intelligence. Nature Reviews Physics 4, 761 (2022).

[2] Krenn, Kottmann, Tischler, Aspuru-Guzik, Conceptual understanding through efficient automated design of quantum optical experiments. Physical Review X 11(3), 031044 (2021).

[3] Ruiz-Gonzalez, Arlt, et al., Digital Discovery of 100 diverse Quantum Experiments with PyTheus, Quantum 7, 1204 (2023).

[4] Krenn, Drori, Adhikari, Digital Discovery of interferometric Gravitational Wave Detectors, in press: Phys. Rev. X (2025), (https://arxiv.org/abs/2312.04258)

[5] Rodríguez, Arlt, Möckl, Krenn, Automated discovery of experimental designs in super-resolution microscopy with XLuminA, Nature Comm. 15, 10658 (2024)

[6] Krenn et al., Forecasting the future of artificial intelligence with machine learning-based link prediction in an exponentially growing knowledge network, Nature Machine Intelligence 5, 1326 (2023)

[7] Gu, Krenn, Interesting Scientific Idea Generation Using Knowledge Graphs and LLMs: Evaluations with 100 Research Group Leaders. arXiv:2405.17044 (2024).

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

Marco Barbieri (Rome Tre University)

Quantum metrology for quantum communications

Quantum metrology is about extracting information from a system. Quantum communications is about sending information over a network. These simple statements reveal a common ground shared by these two applications, but, simply by reading them aloud, one can realise how connecting them is no trivial matter.In this talk we will discuss some recent progress on how concepts and methods from quantum metrology can become beneficial to quantum communications and vice versa. We will present experiments that use photon pairs as means to establish a quantum communication link via their quantum correlations as well as to realise remote quantum sensing. Notably, not only it is possible to use the quality of the sensor to certify the presence of correlations, but also the quality of the correlations can bound the privacy of the sensing.These experiments are first steps towards integrating sensing capabilities in quantum-secure networks, although such a vision necessitates new technical and conceptual tools.

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

Paweł Szczypkowski (IFD UW)

Spatiotemporal light manipulation for nonlinear microscopy

Nonlinear microscopy has revolutionized biological imaging, enabling high-resolution visualization of complex samples. Unlike linear techniques, e.g., multiphoton microscopy offers intrinsic optical sectioning, reduced photodamage, and deeper tissue penetration. However, biological tissues are highly scattering, which fundamentally limits imaging depth and resolution. Overcoming this challenge is crucial for applications ranging from neuroscience to oncology, where clear visualization of deep structures is essential.I will present the three setups for nonlinear imaging: Two-photon microscope that we use for in-vivo imaging, temporal-focusing with super-resolution optical fluctuation imaging for quick and precise imaging, and speckle scanning microscope that together with nonlinearity shows a promise in overcoming the strong scattering.

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