Faculty of Physics University of Warsaw > Events > Seminars > Optics Seminar

Optics Seminar

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room 0.06, Pasteura 5 at 10:15

dr Maciej Gałka (Uniwersytet w Cambridge)

Sound and Turbulence in a 2D Bose Gas

I will present our latest experimental results on driven box-trapped two-dimensional Bose gases.We have observed first and second sound in the system, which is the first such observation in aBerezinskii-Kosterlitz-Thouless (BKT) superfluid. Measurement of the two sound speeds allows theextraction of the superfluid density as a function of temperature, which agrees with the expected universaljump of the superfluid phase-space density at the transition point.In the second part of my talk, I will focus on a strongly driven gas in which a direct turbulent cascadeemerges. Starting from the microscopic dynamics of the discrete low-lying quantum states of the system, wehave observed two key phenomena conceptually associated with the development of turbulence – theemergence of statistical isotropy under anisotropic forcing, and the spatio-temporal scaling of themomentum spectrum.

room 0.06, Pasteura 5 at 10:15

Seminar on March 9 is canceled

room 0.06, Pasteura 5 at 10:15

dr hab. Katarzyna Bielska (UMK Toruń)

Molecular spectroscopy in an optical cavity: pushing the experimental accuracy limits

Molecular spectroscopy provides reference data needed for numerous applications, in particular for remotemeasurements in the Earth's atmosphere, as well as for basic research. In order to correctly model the spectra, there arenecessary full sets of line shape parameters taking into account a number of collisional effects. It turns out, however,that even such basic parameters as line positions and intensities are not known accurately enough in many cases. Mostof the available reference data do not meet the increasingly stringent requirements for applications in the study of theEarth's atmosphere, where relative per-mille accuracy for determining the concentration of various gases is needed.On the other hand, in basic research it is necessary to know the positions of the lines in the optical range even withhertz-level accuracy. Additional difficulties arise from the fact that many of the applications require the study of weakand very weak molecular transitions.Among the possible solutions to these problems there are measurements made in optical cavities, whichenable a significant extension of the effective absorption path length and elimination of some sources of uncertainty,in particular those related to power fluctuations of the probe beam and determination of the absorption path length.Spectroscopy in the cavity allows the measurement of both absorption and dispersion spectra. In the latter case, it ispossible to reference both spectrum axes to atomic frequency standards.Recent results will be presented, where for the first time it was possible to obtain per-mille level accuracy ofcarbon monoxide line intensities: the results of theoretical calculations were verified at the required level of accuracyby three different laboratories. Line positions measurements made with kilohertz and sub-kilohertz accuracy, forDoppler broadened lines and in saturation conditions, respectively, will also be presented.

room 0.06, Pasteura 5 at 10:15

dr Jacek Borysow (Michigan Technological University, Houghton, Michigan USA)

Raman Spectroscopy applied to Atmospheric Research and Medical Diagnostics

In this study, we focused on measuring the temperature in a turbulent flow without disturbing the flow at thetemporal resolution of ~1 second and the spatial resolution of 1 mm3 with accuracy better than 0.1 K. We attempted tomeasure temperatures using pure rotational bands of N2 and O2. We present a highly accurate Raman spectrometerbased on a laser diode tuned to the resonant absorption line of the 85Rb isotope near 780.0 nm. A heated glass cellcontaining Rb atoms was used as an ultra-narrow band atomic absorption notch filter with a bandwidth of 0.1 cm-1 andoptical density as high as four. This filter was placed in front of the spectrograph and blocked up to 99.99% of theelastically scattered laser light, which made it possible to observe the unobscured pure-rotational Raman spectra ofmolecular atmospheric gases. The relative intensities of pure-rotational Raman transitions were then used to inferatmospheric temperature changes.Additionally Spontaneous Raman roto-vibrational spectroscopy was used to measure the ratio of 13CO2 to12CO2 in the breath of a healthy person. We estimated that the changes in the isotopic composition of carbon dioxide atthe level of one part in 100 could be monitored with our apparatus. Experimental data were collected during4 minutes-runs in order to obtain sufficient signal-to-noise ratios. The achieved sensitivities made our Ramanspectrometer suitable for a rapid medical diagnosis with very broad applications. It can be used for numerousbiomedical tests with 13C labelled markers.

room 0.06, Pasteura 5 at 10:15

prof. Asen Pashov (Uniwersytet w Sofii)

Absolute numbering of asymptotic vibrational levels of diatomic molecules from cold-physics experiments

We present a simple method for determination of absolute vibrational numbering ofisolated near dissociation levels in diatomic molecules, usually observed in cold-physicsexperiments. The method is based on the isotope shift and works even when energiesof only two levels from one isotopologue and one level from another isotopologuehave been measured. It is demonstrated with data from recently reported precisemeasurements of binding energies of levels lying close to the dissociation limits inultracold Yb2, CsYb, RbSr, and RbYb molecules. Its predictions agree with those ofmuch more elaborate multi-isotope potential curve

room 0.06, Pasteura 5 at 10:15

dr Benjamin Brecht (Uniwersytet w Paderborn)

Time-multiplexed photonic quantum systems

Quantum photonics has seen rapid developments during recent years. The fundamentaldevelopments have been honoured with this year’s Nobel Prize in Physics, but since thenprogress has accelerated. To date, researchers routinely create multi-photon entangled statesin their laboratories, measure with unequal precision, communicate securely over longdistances, and have even demonstrated a computational quantum advantage.The main bottle necks that quantum photonics is facing at this point are non-deterministic operations and losses. In discrete variable quantum optics, the latter roughlyamount to the prior, as photon loss usually means an unsuccessful operation. Multiplexingstrategies are known to provide a solution to this problem. One particularly appealingmultiplexing method is time-multiplexing, whereby hardware components are used manytimes. This leads to an advantageous decrease in experimental overhead when compared to,e.g., spatial multiplexing where simply many components are built and used in parallel.In this presentation, I will discuss our recent work on time-multiplexed photonicquantum systems with active feed-forward and quantum feedback. Our experimental toolboxhas enabled us to demonstrate an exponential increase in the generation rate of multi-photonGHZ states which can form the basis for photonic quantum computing architectures, anincreased generation rate of multi-photon Fock states with the potential to create more exoticquantum states, and flexible high-dimensional quantum systems with up to 10 photons in upto 64 modes.

room 0.06, Pasteura 5 at 10:15

dr Krzysztof Kaczmarek (ORCA Computing Imperial College London)

ORCA Computing – Scalable quantum computing powered by quantum memories

ORCA Computing's mission is to build photonic quantum computing devices, from smallNISQ processors to large-scale fault-tolerant quantum computers. In this talk, I will presentthe photonic approach to quantum computing, discuss its advantages and challenges withrespect to other technology platforms, and show how ORCA's quantum memory can helpovercome these challenges. I will also present ORCA's first complete quantum computingsolution, the PT-Series, which implements the boson sampling model of quantumcomputing. The PT-Series is particularly well suited for implementing a wide range ofquantum variational algorithms for machine learning, and I will discuss these algorithms andsome of their applications

room 0.06, Pasteura 5 at 10:15

dr Jan Kołodyński (Centrum Nowych Technologii)

Noisy atomic magnetometry in real time: from linear-classical to nonlinear-quantum models

In my talk I will summarize recent results obtained with my group, in which we combinequantum description of continuously monitored atomic sensors with efficient techniques ofBayesian statistical inference, in order to track fluctuating signals in atomic magnetometry. Iwill start by discussing a linear-classical model in which it is sufficient to use KalmanFiltering (KF) methods to optimally estimate signals encoded in the light pumping theatomic ensemble. However, I will demonstrate how this scenario may be directly generalizedwith use of the Extended Kalman Filter (EKF) to track magnetic fields, i.e. the Larmorfrequency. Importantly, I will afterwards move onto the nonlinear-quantum setting in which,thanks to the phenomena of measurement back-action and continuous spin-squeezing, theclassical limits imposed on precision may be spectacularly breached. On one hand, I willshow how to determine then the correct ultimate noise-induced limits by employing tools ofquantum information theory. On the other, I will demonstrate how to achieve such quantum-enhanced resolutions by resorting to the effective quantum stochastic description of thedynamics involving measurement-based feedback and the EKF

room 0.06, Pasteura 5 at 10:15

dr Maciej Kowalczyk (Politechnika Wrocławska i Ludwig Maximilian University of Munich)

Generation and control of single-cycle mid-infrared waveforms

The generation of ultrashort laser pulses comprising a mere few or even a single electric-field oscillation,and the possibility to shape such electric-field waveforms are key technologies for investigating andcontrolling fundamental light-matter interactions on the sub-femtosecond time scale. Extending the sub-cycle waveform control from the previously - demonstrated near-infrared (near-IR) to the mid-infrared (mid-IR) spectral range is crucial for several applications, including next-generation light-wave-driven electronicsignal processing in low-bandgap highly-doped semiconductors and field-resolved spectroscopy ofbiological systems.Here, we present a novel approach for the generation and control of single-cycle mid-IR waveforms.Down-conversion of carrier-envelope-phase (CEP) stable 7-fs single-cycle pulses from a Cr:ZnS laser in asingle ZnGeP2¬¬ crystal provides a 3.7-octave supercontinuum, stretching from the near-IR to the mid-IRfingerprint region. By exploiting the CEP-dependence of the underlying cascaded intra-pulse difference-frequency-generation (IPDFG) we can continuously adjust the waveforms of the single-cycle mid-IRtransients. The unprecedented CEP-stability (5.9 mrad) of our Cr:ZnS driving laser results in highlyreproducible control over the waveform generation

room 0.06, Pasteura 5 at 10:15

dr Przemysław Głowacki (Politechnika Poznańska)

Investigations of the electronic structure of selected elements in terms of applications in optical clocks

The scientific aim of talk will be presentation of the results of investigation the structure of selected elements: chromium, manganese andthorium, in terms of their applications in optical atomic and nuclear clocks. Research work was carried out at the Poznań University ofTechnology and at PTB Braunschweig, Germany.One of the tasks was to obtain a possibly complete description of the electronic energy structure of the atoms of selected elements with an open3d shell - chromium and manganese [H1-H8], which could form the basis of an effective search for electronic level systems with specificproperties necessary for applications in quantum engineering and metrology, in particular for optical atomic clocks. The remaining part of thepresentation will include the works related to the pioneering optical nuclear clock project, based on the transition between the ground and theexcited (isomer) state transition in 229 thorium nucleus, which was developed in cooperation with the Prof. E. Peik’s research group from PTB(Germany), leading in this field.In the case of the chromium atom, comprehensive studies of the hyperfine structure will be presented, performed by laser spectroscopy on anatomic beam apparatus: the methods of double optical-microwave resonance ABMR-LIRF (Atomic Beam Magnetic Resonance detected byLaser Induced Resonance Fluorescence) and LIF (Laser Induced Fluorescence) [H1-H3]. Based on the collected experimental results and thedata from literature sources, a semi-empirical analysis of the electronic structure of the chromium atom was carried out. This allowed to proposethe use of the forbidden transition between selected levels of the chromium atom as a possible optical clock transition along with possibleschemes of its detection [H4].For the manganese atom, the results of experimental studies of the hyperfine structure will be presented, performed with the use of the LIFmethod on an atomic beam [H5,H6] and in a hollow cathode lamp [H8]. In this case, the theoretical semi-empirical analysis of the structure ofthis element in terms of radiative parameters (such as oscillator strengths, transition probabilities and the levels’ lifetimes) allowed to proposethree possible optical clock transitions and possible cooling schemes [H7].The presentation will also show the basic assumptions regarding the implementation of an optical nuclear clock, both in research on trappedTh+,Th2+, Th3+ ions in linear traps [H9], as well as the concept of its implementation based on a crystal volume-doped with Th4+ ions, (e.g. CaF2:Th4+), or in a simpler version - a surface-doped crystal [H10].H1 A. Krzykowski, P. Głowacki Experimental study of radio frequency power broadening in ABMR-LIRF method, Elektronika 6: 31-34 (2011), (IF = —, MNiSW8 pkt.) https://www.sigma-not.plH2 A. Krzykowski, P. Głowacki, A. Jarosz Precise measurements of the hyperfine structure of the levels belonging to the terms 3d54s 5G and 5P in Cr(I), ActaPhys. Pol. A, 122, p. 78-81 (2012), (IF = 0.444, MNiSW 15 pkt.) doi: 10.12693/APhysPolA. 122.78H3 P. Głowacki, A. Krzykowski, A. Jarosz Investigation of the hyperfine structure of electronic levels in chromium atom, Eur. Phys. J. Special Topics 222, 2345-2351 (2013), (IF=1.862, MNiSW 30 pkt.) doi: 10.1140/epjst/e2013- 02015-xH4 P. Głowacki, D. Stefańska, M. Elantkowska, J. Ruczkowski Proposed clock transition in atomic chromium and the possible detection schemes Journal ofQuantitative Spectroscopy and Radiative Transfer 291, 108331 (2022), (IF = 2.342, MEiN* 100 pkt.) doi: 10.1016/j.jqsrt.2022.108331H5 P. Głowacki, D. Stefańska, M. Elantkowska, J. Ruczkowski Hyperfine structure studies of the electronic levels of the manganese atom. I. Even-parity levelsystem Journal of Quantitative Spectroscopy and Radiative Transfer 249, 107013 (2020), (IF = 2.468, MEiN∗ 100 pkt.) doi: 10.1016/j.jqsrt.2020.107013H6 P. Głowacki, D. Stefańska, J. Ruczkowski, M. Elantkowska Hyperfine structure studies of the electronic levels of the manganese atom. II. Odd-parity levelsystem Journal of Quantitative Spectroscopy and Radiative Transfer 253, 107138 (2020), (IF = 2.468, MEiN∗ 100 pkt.) doi: 10.1016/j.jqsrt.2020.107138

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