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Seminarium Optyczne

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

Gediminas Juzeliūnas (Institute of Theoretical Physics and Astronomy, Vilnius University, Vilnius, Lithuania)

Sub-wavelength lattices for ultracold atoms

Traditionally, optical lattices are created by interfering two or more light beams, so that atoms are trapped at minima or maxima of the emerging interference pattern depending on the sign of the atomic polarizability [1]. The characteristic distances over which such lattice potentials change are limited by diffraction and thus cannot be smaller than half of the optical wavelength λ. The diffraction limitation can be overcome and subwavelength lattices can be created using coherent coupling between atomic internal states [2-9]. In particular, recent experiments demonstrated deeply subwavelength lattices using atoms with N internal states Raman-coupled with lasers of wavelength λ [7]. The resulting unit cell was N times smaller compared to the usual λ/2 periodicity of an optical lattice. In the present talk we will discuss various ways to produce subwavelength lattices and effects manifesting in these lattices. In particular, we will present our recent work on periodically driven subwavelength lattices [8], as well on two-dimensional subwavelength lattices affected by the synthetic magnetic flux [9]. Ongoing research on many-body effects in subwavelength lattices will also be discussed.[1] I. Bloch, Nature Physics 1, 23 (2005).[2] M. Łącki et al., Phys. Rev. Lett. 117, 233001 (2016).[3] F. Jendrzejewski et al., Phys. Rev. A 94, 063422 (2016).[4] Y. Wang et al, Phys. Rev. Lett. 120, 083601 (2018).[5] E. Gvozdiovas, P. Račkauskas, G. Juzeliūnas, SciPost Phys. 11, 100 (2021).[6] P. Kubala, J. Zakrzewski and M. Łącki, Phys. Rev. A 104, 053312 (2021). [7] R. P. Anderson et al, Physical Review Research 2, 013149 (2020).[8] D. Burba, M. Račiūnas, I. B. Spielman and G. Juzeliūnas, Phys. Rev. A 107, 023309 (2023).[9] E. Gvozdiovas, I. B. Spielman and G. Juzeliūnas, Phys. Rev. A 107, 033328 (2023).

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

mgr Agata Wojciechowska (IFD UW)

Exotic ultralong-range Rydberg molecules

The discovery of Rydberg matter empowers prospects in ultracold science. Recently, scientists tookanother step forward by measuring the Rydberg series of highly magnetic lanthanide – Er. We intend to examinethe complex entity of the ultralong-range Rydberg molecule and search for intriguing energy structure, noveltransitions, and unusual magnetic properties. In our work, we first describe Er with Multichannel QuantumDefect Theory to calculate the energy spectrum of the Rydberg molecule composed of excited Er and groundstate Rb. We use the perturbation theory due to the lack of sufficient experimental data for a general model. Astep towards developing a proper model is understanding molecules with a two-valence electron Rydberg atom.Here, the Hg*Rb molecule serves as a platform. We present promising energy spectra with easily accessibletrilobite states and approach homonuclear Hg molecules calculations

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

dr Jacek Dobrzyniecki (Wydział Fizyki UW)

Quantum simulation of the central spin model with a Rydberg atom and polarmolecules in optical tweezers

Central spin models, where a single spinful particle interacts with a spin environment, find wideapplication in quantum information technology and can be used to model e.g. the decoherence of a qubit in adisordered environment. We propose a method of realizing an ultracold quantum simulator for the central spinmodel. The proposed system consists of a single Rydberg atom (central spin) and polar molecules (environmentspins), coupled via dipole-dipole interactions. By mapping internal particle states to spin states, spin-exchanginginteractions can be simulated. Precise control over the model can be exerted by directly manipulating theplacement of environment spins. As an example, we consider a ring-shaped arrangement of environment spins,and show how the system's time evolution is affected by the tilt angle of the ring

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

dr Tobias Grass (Donostia International Physics Center, San Sebastian, Hiszpania)

Old model, new fun - quantum simulation of Hubbard models

The Hubbard Model in all its variations plays a central role in the description of strongly correlatedmany-body systems. Despite its simple form, the solution of the model remains a challenge for analytical andnumerical methods. Quantum simulation has been established as an alternative solution method in the last 20years. My talk takes a comprehensive look at this development and introduces both atomic and electronic many-body systems suitable for quantum simulation of Hubbard models. In particular, the focus is on variousextensions of the model, such as electron-phonon interaction, long-range interactions, two-layer geometry, whichplay an important role for superconductivity or superfluidity, as well as for exotic phases with broken latticesymmetries.

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

Dr Andreas Schindewolf (Max Planck Institute for Quantum Optics, Garching, Germany)

Dipolar Molecules — State of the Art

With this talk, I will provide a broad overview of the recent exciting developments in the field of dipolarmolecules. Although dipolar molecules have been a hot topic for more than 10 years, only recently the field hasentered the quantum degenerate regime. A reasonable understanding was acquired for why supposedly stablemolecules undergo inelastic collisions and methods have been developed to suppress collisional lossmechanisms. These new techniques set the stage to finally study quantum many-body systems with dipolarmolecules

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

dr Julian Wienand (Ludwig-Maximilians-Universität, München i Max-Planck-Institute for Quantum Optics, Garching)

Thermalization of large bosonic quantum systems under the microscope

How does a quantum many-body system reach thermal equilibrium after a quench? And how are theequilibrium properties related to the microscopic parameters of the system? While it is generally difficult toaddress this question using classical numerical methods, quantum simulators can provide alternative ways, whichmay further facilitate the development of new effective theoretical descriptions. Quantum gas microscopy inparticular offers unique insights into thermalization dynamics via access to correlation functions and fullcounting statistics. We use a new Cesium quantum gas microscope with small lattice spacing to explore therelaxation dynamics of large quasi-one-dimensional bosonic quantum many-body systems. In particular, weprepare ladder systems with a length of up to 40 sites at half filling and tunable coupling between the legs. Thisallows us to study the crossover between integrable and chaotic dynamics. Using an unsupervised machine-learning algorithm we reconstruct the site-resolved density distribution with high fidelity and study the dynamicsvia local densities, density-density correlation functions and particle number fluctuations. While the local meandensity relaxes within few tunneling times, we find that global equilibrium is reached on much slower timescales.The scaling of the equilibration time as a function of subsystem size provides an indication of the intrinsictransport dynamics enabling us to investigate the crossover from ballistic to diffusive dynamics as the couplingbetween the legs of the ladder is increased.

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

prof. Moti Fridman (Bar Ilan University, Izrael)

Quantum temporal optics - how to take quantum optics into the time-domain

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

dr Łukasz Sterczewski (Politechnika Wrocławska)

Two-photon imaging of soliton dynamics

Optical solitary waves (solitons) represent one of the key concepts in laser physics. They result froman interplay between intracavity dispersion and nonlinearity at high optical intensities. However, opticalsolitons have the striking ability to form transient or stable pulse aggregates referred to as soliton molecules.Despite their perspective use in quantum memories or next-generation telecommunication systems, from alaser development perspective they pose a significant difficulty. The multi-pulse emission of laser lighthinders nonlinear frequency conversion and induces pronounced amounts of noise. It is also not trivial todetect such structures using conventional techniques like intensity autocorrelation or spectral analysis due toinstrument limitations. Therefore, their presence often goes unnoticed. During the talk, we will discuss anovel, easy-to-implement tool for rapid, real-time diagnostics of pulsed lasers that relies on two-photoninteraction on a nonlinear photodetector. The technique enables us to probe soliton molecules spaced byfemtoseconds to nanoseconds at arbitrary wavelengths and over arbitrary time scales using a conventionaltelecom-grade laser oscillator and a low-bandwidth oscilloscope. We will discuss the application of ourtechnique to monitoring simple soliton triplets and quadruplets along with more complex systems likemolecular crystals or soliton rains

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

dr Maciej Pieczarka (Politechnika Wrocławska)

Bose-Einstein-like phase transition in semiconductor lasers

Photons were the first bosons to be considered under the quantum statistics known today as the Bose-Einstein statistics. However, they were one of the most recent quantum gases to undergo Bose-Einsteincondensation in a controlled environment, which was achieved recently in a microcavity filled with a 6Grhodamine solution [1]. Since these pioneering observations, the principle of light thermalisation andcondensation in optical cavities has been anticipated to be a much more common phenomenon. In this talk, Iwill present our most recent results on the Bose-Einstein condensation of photons in a well-knownsemiconductor device, the vertical-cavity surface-emitting laser (VCSEL). We measured a Bose-Einsteintype of behaviour when crossing the critical phase-space density and observed a thermalised distribution ofphotons, equilibrated to temperatures lower than those of the device. Nevertheless, the measuredspectroscopic and caloric properties show all predicted effects for a Bose-Einstein condensate phasetransition in thermal equilibrium. I will discuss our observations in context of a driven-dissipativenonequilibrium Bose-Einstein condensation phenomenon [2].[1] Klaers, J. et al., Nature 468, 545–8 (2010).[2] Shishkov, V. Y. et al., Phys. Rev. Lett. 128, 065301 (2022)

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

(UMK Toruń)

dr. Tomasz Wasak

Quantum kinetic theory of Fermi polarons

A mobile impurity immersed into a degenerate Fermi gas is a paradigmatic problem in many-bodyphysics. Dressing of the quantum impurity by a cloud of particle-hole excitations of the environment leadsto formation of quasi-particles which are called polarons. The observations of these quasi-particles inexperiments with ultracold atomic gases or with two-dimensional monolayer semiconductors renewedinterest in the field of quantum impurities. The description of polaron physics in these systems was based onequilibrium theory or wave function techniques. However, a non-equilibrium treatment is needed whichwould include not only coherent quantum processes of quasi-particle formation but also time-dependentexternal drive or even pump and loss.In the talk I will describe our approach to non-equilibrium Fermi polaron physics. Based on non-equilibrium quantum field theory, we derived a kinetic equation that includes processes of polaron formationand external fields, and it allows for studying relaxation of polarons and their non-equilibrium distributions.In particular, in the context of ultracold atomic gases, we apply our theory of driven polarons to recentexperiments with ultracold atoms, where Rabi oscillations between a Fermi-polaron state and a non-interacting level were reported. We find a good quantitative agreement between our predictions and theavailable experimental data without any fitting parameter

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