LPHYS'24.    Plenary Speakers:

  1. Time Reversed Quantum Metrology


    It is well recognized that quantum physics can be used to build better sensors. Such sensors can be for parameters, like phases, forces, fields that correspond to the unitary evolution of the system or for parameters like absorption, scattering that require description in terms open system dynamics. The framework of the quantum Fisher information enables one to obtain best estimates of the parameters and then one can design experiments that can reach Cramer- Rao bounds. I would highlight the importance of the quantum states used as probes, and the importance of the quantum-ness of the measurement schemes. It turns out that in many cases the schemes based on time reversed metrology saturate Cramer-Rao bounds. I would discuss the importance of squeezed states of bosonic systems like photons, ions and cat states of qubits for metrological applications. I would present results on the quantized motion of trapped ions and on quantum advantage in the determination of phases, absorption and scattering parameters.

  2. Random Lasers as platforms to study Universal Photonic Phase-Transitions

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      Cid B de Araújo

      Universidade Federal of Pernambuco, Physics Department, Recife, PE, Brazil

    Random Lasers (RLs) are light sources that operate due to the multiple scattering of light in disor-dered gain media that provide the feedback for laser action. No optical cavity of conventional mirrors contributes to the optical feedback. In this talk I will review advances in the RLs research with examples of systems operating in pulsed and continuous-wave regimes. The mechanisms governing the behavior of RLs based on colloidal-suspensions of dielectric nanoparticles and luminescent dyes, powders consisting of nanocrystals doped with rare-earth ions, and random fiber lasers, will be discussed. The contribution of wave-mixing will be exemplified by the multi-wavelength emission and tunable UV-blue RL gene-ration from neodymium-doped nanocrystals. Wave-mixing among lasing modes also influence the RLs intensity fluctuations. The observation of Lévy distribution of intensity fluctuations and the Replica-Symmetry-Breaking transition from the photonic paramagnetic phase to the photonic spin-glass phase are interesting examples of the RLs complex behavior that will be also discussed.

  3. Broadcasting single-qubit and multi-qubit-entangled states: authentication, cryptography, and distributed quantum computation

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      János A. Bergou

      Department of Physics and Astronomy, Hunter College of the City University of New York, New York, NY, USA
      Graduate Center of the City University of New York, New York, NY, USA

    The no-cloning theorem forbids the distribution of an unknown state to more than onereceiver. However, quantum entanglement assisted with measurements provides various pathways to communicate information to parties within a network. For example, if the sender knows the state, and the state is chosen from a restricted set of possibilities, a procedure known as remote state preparation can be used to broadcast a state. In this talk, we first examine a remote state preparation protocol that can be used to send the state of a qubit, confined to the equator of the Bloch sphere, to an arbitrary number of receivers [1]. The entanglement cost is less than that of using teleportation to accomplish the same task. We also present variations on this task: probabilistically sending an unknown qubit state to two receivers, sending different qubit states to two receivers, sending qutrit states to two receivers, and discuss some applications of these protocols. Next, we generalize the basic broadcasting protocol to broadcast product and multi-partite entangled quantum states in a network where, in the latter case, the sender can remotely add phase gates or abort distributing the states [2]. The generalization allows for multiple receivers and senders, an arbitrary basis rotation, and adding and deleting senders from the network.

    We also discuss the case where a phase to be applied to the broadcast states is not known in advance but is provided to a sender encoded in another quantum state. Applications of broadcasting product states include authentication and three-state quantum cryptography. We also study the distribution of a single multiqubit state shared among several receivers entangled with multi- qubit phase gates, giving the graph states as an example. As an application, we discuss the distribution of the multi-qubit GHZ state. We close with a discussion of the capabilities and limitations of implementations using linear optical quantum networks [3].

    [1] Mark Hillery, János A Bergou, Tzu-Chieh Wei, Siddhartha Santra and Vladimir Malinovsky, Phys. Rev. A 105, 042611 (2022)
    [2] Hiroki Sukeno, Tzu-Chieh Wei, Mark Hillery, János A Bergou, Dov Fields and Vladimir S Malinovsky, Phys. Rev. A 107, 062605 (2023)
    [3] Dov Fields, János A Bergou, Mark Hillery, Siddhartha Santra, and Vladimir S Malinovsky, Phys. Rev. A 106, 023706 (2022)

  4. High harmonic generation: the route towards bright sources in the soft X-ray spectral range


    With the process of High Harmonic Generation (HHG) in gases, the wavelength of a femtosecond (1 fs = 10–15 s) driving laser (from the UV to the mid-IR) can be up-converted to generate fully coherent, ultrashort pulses with spectra spanning through the extreme ultraviolet (XUV) and even into the soft X-rays. Not only can the emitted XUV pulses have durations in the order of attoseconds (1 as = 10–18 s), but they are also synchronized with the electric field of the driving laser within a very small fraction of the period of its carrier wavelength. Over the past 20 years, this has allowed researchers to perform experiments with temporal resolution on the order of a few attoseconds, i.e., a very small fraction of the typical optical period of the driver (e.g., 2.7 fs). The Nobel Prize in Physics 2023 was awarded for the experimental methods for the generation and characterization of attosecond pulses of light.

    However, the main limitation of HHG is the extremely low efficiency of conversion, leading to low photon flux, especially at higher photon energies – in the hundreds of electronvolts, or few nanometer wavelengths. Significant effort is being put into the generation of soft X-ray pulses with both extended spectral range and increased photon flux. Several solutions, based on driving pulses with either longer (mid-IR) or shorter (VIS, UV) wavelengths, or even by finely shaping the electric field of the driver, have been thoroughly investigated both theoretically and experimentally.

    In the perspective of power-scaling HHG sources with extended spectral range, it is important to consider not only how the parameters of the driving pulse affect the HHG conversion process, but also how, and how efficiently, the driving pulses can be obtained – usually by frequency-shifting and nonlinear post-compression techniques applied to different laser sources.

  5. The Wonderful World of Random Lasers and Random Fiber Lasers


    Random Lasers (RLs) are coherent light sources whose feedback mechanism relies on light scattering in a strongly scattering media in the presence of a gain medium, instead of a pair of fixed mirrors. Upon appropriate pumping, inversion population and amplification precede the optical feedback such as the gain overcomes the loss as in conventional lasers. As reviewed in [1], where most of the historical background and theoretical/experimental developments until June 2021 can be read, RLs, as well as Random Fiber Lasers (RFLs) have become an important tool for photonic studies. As light sources, RLs and RFLs have been demonstrated in all 1D, 2D and 3D configurations, and well characterized regarding threshold, line narrowing/emitted intensity versus excitation intensity, polarization, spatial and temporal coherence, photon statistics (which has been shown to be Poissonian) and operation in the continuous wave or pulsed regime. Regarding RL materials, as long as there is a suitable gain medium (dye, rare earth doped glasses and crystals, semiconductors, quantum dots, etc.) and a scattering medium (which can be the same as the gain medium or external to it) a myriad of RLs/RFLs have been demonstrated [1]. As for RFLs, even the Rayleigh scattering in a few kms fiber length is enough to provide optical feedback, and intrinsic Raman or Brillouin processes provide the gain for laser action. Recently, we have demonstrated a transform limited mode-locked random fiber laser [2]. Flexible RLs in 2D have also been exploited using biomaterials as hosts, and of course RFLs (1D) are intrinsically flexible by nature. Regarding applications, RLs and RFLS have been exploited for speckle-free imaging, which is an important feature for diagnostic by imaging. A variety of sensing devices based on RLs/RFLs have been reported, including biosensors, powder delivery rate sensor, dopamine detection, among others. In optical communications, RFLs optical amplifiers have been demonstrated to perform better than conventional optical fiber amplifiers, as reviewed in [1] and refs therein. Finally, RLs and RFLs have been exploited as a photonic platform to study, by analogy, turbulence, photonic spin glass, Lévy statistics, Floquet states and extreme events. The connection between photonic turbulence and spin glass behavior of light has shown to bridge the two subjects and, through experiments using RFLs, have been highlighted in connection with the recently awarded 2021 Nobel Prize in Physics [3]. All these exciting features of the wonderful world of RLs and RFLs will be touched upon during this lecture.

    [1] Anderson S L Gomes, André L Moura, Cid B de Araújo and Ernesto P Raposo, Prog. Quant. Electron. 78, 100343 (2021)
    [2] Jean Pierre von der Weid, Marlon M. Correia, Pedro Tovar, Anderson S L Gomes and Walter Margulis, Nat. Commun. 15, 177 (2024)
    [3] A S L Gomes, C B de Araújo, A M S Macêdo, I R R González, L de S Menezes, P I R Pincheira, R Kashyap, G L Vasconcelos and E P Raposo, Light Sci. Appl. 11, 104 (2022)

  6. Quantum Simulation of Many-Body States of Matter with Ultracold Atoms


    Models of quantum many-body phases of matter have been realized using fermionic ultracold atoms instead of electrons and engineered optical potentials that emulate a crystal lattice. Quantum simulation of this kind takes advantage of the innate capability to adhere to a theoretical model, while the tunability of model parameters enables quantitative comparison with theory. For example, repulsively interacting spin-1/2 fermions confined to one-dimensional (1D) tubes realize a Tomonaga-Luttinger liquid. The low-energy excitations are collective, bosonic sound waves that correspond to either spin-density or charge-density waves that, remarkably, propagate at different speeds. Such a spin-charge separation has been observed in electronic materials, but a quantitative analysis has proved challenging because of the complexity of the electronic structure and the unavoidable presence of impurities and defects in electronic materials. In collaboration with our theory colleagues, we made a direct theory/experiment comparison and found excellent agreement as a function of interaction strength [1]. It was necessary to include nonlinear corrections to the spin-wave dispersion arising from back-scattering, thus going beyond the Luttinger model. More recently, we explored the disruption of spin correlations with increasing temperature [2], an effect that destroys spin-charge separation. We are now working near a p-wave resonance to realize p-wave pairs.

    [1]Ruwan Senaratne, Danyel Cavazos-Cavazos, Sheng Wang, Feng He, Ya-Ting Chang, Aashish Kafle, Han Pu, Xi-Wen Guan and Randall G Hulet, Science 376, 1305 (2022)
    [2]Danyel Cavazos-Cavazos, Ruwan Senaratne, Aashish Kafle and Randall G Hulet, Nat. Commun. 14, 3154 (2023)

  7. Quantum Light: Coherence, Photon Statistics and Phase Space


    Gerd Leuchs studied physics at the Universities of Cologne and Munich. His Ph.D. thesis dealt with the fine structure splitting of sodium Rydberg atoms. He received the Habilitation degree at the University of Munich on multiphoton processes in atoms. After staying in the USA and Switzerland, Gerd Leuchs became a full professor of physics at the University Erlangen-Nuremberg in Germany. Since 2009, he has been a director at the Max Planck Institute for the Science of Light, and since 2011, he has been a professor adjunct at the University of Ottawa. He is a member of the German and the Russian Academy of Sciences and holds honorary degrees from Danish Technical University and St. Petersburg State University. He won the 2005 Quantum Electronics and Optics Prize of the European Physical Society and the 2018 Herbert Walther Prize, a joint award by Optica (formerly OSA) and DPG. He is a fellow of the European Optical Society, Optica, and the Chinese Optical Society. In 2012, he was awarded the Cross of Merit of the Federal Republic of Germany, and in 2018, he was appointed a member of Bavaria’s Maximilian Order. He is the 2024 president of Optica. His research spans the whole range from classical to quantum optics, with emphasis on the limits of focusing, photon-atom-coupling and quantum noise reduction of light.


    The three topics coherence, photon statistics and phase space distribution are intimately related and closely connected to the properties of the quantum vacuum. Here we will pick three different scenarios which underline this relation: two experimental results and one speculative consideration. The first one [1] is about the nature of spontaneous emission.  Wigner and Weisskopf treated spontaneous emission perturbatively as an irreversible process, which raises the question whether or not there coherence between the light emitted by a single atom spontaneously into different direction: the experiment gives the answer. The second scenario [2] is a simultaneous measurement of the phase space distribution function and the intensity correlation in a light field which can be tuned between from a squeezed state to a thermal State. The intensity correlation is determined in two different ways and the results are compared: one way is to measure the intensity correlation directly and the other way is to calculate the intensity correlation from the measured Wigner function. We focus on weak squeezing for which the g(2) function diverges. The third scenario, the speculative consideration [3] is to treat the modern vacuum as a dielectric and show that this provides a phenomenological approach to determining the speed of  light, the permittivitty of the vacuum and the fine structure constant.

    [1] Gerd Leuchs, Luis L Sánchez-Soto, Martin Fischer, Markus Sondermann and Ralf Menzel, to be published
    [2] Gerd Leuchs, Luis L Sánchez-Soto, Hanna Le Jeannic, Kun Huang, Julien Laurat and Mojdeh Shikhali Najafabadi, to be published
    [3] Gerd Leuchs, Margaret Hawton and Luis L Sánchez-Soto, Physics 5, 179 (2023)

  8. Quantum entanglement and beyond

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      Jian-Wei Pan

      University of Science and Technology of China, Hefei, Anhui, China

    Quantum information science and technology are emerging and fascinating technologies formed by combining coherent manipulating of individual quantum systems and information technology, which enables secure quantum cryptography (quantum communication), super-fast quantum computing (quantum computation), and improving measurement precision (quantum metrology) etc., to beat classical limits.

    For fundamental aspect, one is led to the conception of quantum entanglement. The appeared ‘spooky action at a distance’ phenomena referred by Einstein, is often explained by seemingly reasonable assumptions of ”local realism”. The inequalities proposed by John Bell and others provide immediate tests for correctness of quantum mechanics. Many efforts are addressing loophole-free tests of Bell inequalities, which tries to close various loopholes, in which some of loopholes are still needed to be addressed including freedom of choice loophole, the collapse locality loophole. Well, the final test is on-going, many developed ground-breaking technologies for coherent manipulation of quantum systems offers elegant and feasible solutions for satisfying increasing needs of computational power and information security.

    Based on state-of-the-art fiber technology and rich fiber resources, we have managed to achieve prevailing quantum communication with realistic devices in real-life situation. This constitutes demonstrations by developing decoy state scheme over 100 km firer, extending its employment in the metropolitan area network, as well as maintaining Measurement Device Independent QKD (MDI-QKD) over 400 km. At the meantime, we are also developing practically useful quantum repeaters that combine entanglement swapping, entanglement purification, efficient and long-lived quantum memory for the ultra-long distance quantum communication. Another complementing route is to attain global quantum communication based on satellite. We have spent the past decade in performing systematic ground tests for satellite-based quantum communications. Our efforts finally ensure a successful launch of the Micius satellite. Three major scientific missions have been finished, which includes achieving QKD between satellite and ground station at thousand kilometer scale, achieving satellite-based entanglement distribution between two ground stations separated by a distance of 1200 km, achieving quantum teleportation from ground to satellite over 1400 km. Moreover, using Micius satellite as a trustful relay, the intercontinental QKD between Beijing and Vienna over a distance of 7600 km has also been realized.

    Future Prospects include building a global quantum communication infrastructure with satellite and fiber networks, enormous spatial resolution and global precise timing information sharing networks with applications for the global quantum communication network, ultra-precise optical clocks in outer space to detect gravitational wave signal with lower frequency.

  9. Landau-Zener transitions, Hawking radiation and number theory


    Landau–Zener-transitions are an essential tool in atom optics, and in particular, in accelerated optical lattices. It is amazing that despite its simplicity, the derivation of the well-known Landau-Zener-formula for the transition probability amplitude is rather involved, independent of the approach pursued. In the present talk, we employ the Markov approximation and the well-known Fresnel-integral to derive [1] in ‘’one-line” the familiar expression for the Landau-Zener-formula. Moreover, we provide numerical as well as analytical justifications for our approach, and identify three characteristic motions of the probability amplitude in the complex plane. In addition, we make the connection to Hawking radiation [2] and number theory, in particular, the Riemann hypothesis [3].

    [1] Eric P Glasbrenner and Wolfgang P Schleich, J. Phys. B - At. Mol. Opt., 56, 104001 (2023)
    [2] Marlan O Scully, Stephen Fulling, David M Lee and Anatoly A Svidzinsky, Proc. Natl. Acad. Sci. USA, 115 8131 (2018)
    [3] Michael E N Tschaffon, Iva Tkáčová, Helmut Maier and Wolfgang P Schleich, in: Roberta Citro, Maciej Lewenstein, Angel Rubio, Wolfgang P Schleich, James D Wells and Gary P Zank (Eds.), Sketches of Physics, Lecture Notes in Physics 1000, Springer Heidelberg, 2023, p. 191

  10. Observing the quantum topology of light

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      Da-Wei Wang

      Zhejiang University, School of Physics, Hangzhou, China

    Topological photonics provides a powerful platform to explore topological physics beyond traditional electronic materials and shows promising applications in light transport and lasers. Classical degrees of freedom are routinely used to construct topological light modes in real or synthetic dimensions. Beyond the classical topology, the inherent quantum nature of light provides a wealth of fundamentally distinct topological states. In this talk I will introduce the experiment on topological states of quantized light in a superconducting circuit, with which one- and two-dimensional Fock-state lattices are constructed. We realize rich topological physics including topological zero-energy states of the Su-Schrieffer-Heeger model, strain-induced pseudo-Landau levels, valley Hall effect, and Haldane chiral edge currents. Our study extends the topological states of light to the quantum regime, bridging topological phases of condensed-matter physics with circuit quantum electrodynamics, and offers a freedom in controlling the quantum states of multiple resonators.

  11. Embracing the Potential of Nonlinear Integrated Photonics Beyond Silicon: Advantages and Limitations

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      Gustavo Wiederhecker

      Universidade Estadual de Campinas, Department of Applied Physics, Campinas, SP, Brazil

    Nonlinear integrated photonics is a rapidly evolving field that offers exciting opportunities for novel devices and applications, promising a realm of possibilities beyond traditional silicon-only approaches. In this presentation, we journey through some recent results in this field, uncovering both its inherent advantages and the challenges it presents. From the interplay of light and matter on the nanoscale to 2 the practical applications in sensing, communication, and computation, we delve deep into the potential and flaws that nonlinear integrated photonics bring in.

  12. Nonlinear optics of stochastic field waveforms


    Aleksei Zheltikov received his PhD and Doctor of Science degrees from M.V. Lomonosov Moscow State University. He has been a full professor at M.V. Lomonosov Moscow State University since 2000 until 2022. He served as a group leader at the Russian Quantum Center, head of the Laboratory of Neurophotonics at Kurchatov Institute, and head of the Laboratory of Fiber Optics for Quantum Technologies at A.N. Tupolev Kazan Technical University. Since 2010, he is a professor at Texas A&M University. His research is focused on ultrafast nonlinear optics, quantum physics, and biophotonics.


    Methods of statistical analysis offer new insights into a nonlinear dynamics of stochastic optical field waveforms, providing a framework that helps understand supercontinuum generation driven by stochastic laser pulses, as well as dynamic instabilities and filamentation of stochastic laser beams. Unlike deterministic self-focusing, whose criterion is expressed in terms of a well-defined self-focusing threshold, its stochastic counterpart is a probabilistic process whose combined probability for a sample of N laser pulses builds up as a function of N. We show that the ratio 𝑃/𝑃cr of the laser peak power 𝑃 to the critical power of self-focusing 𝑃cr, which plays a central role in deterministic self-focusing, keeps its status as a key governing parameter in stochastic self-focusing. However, in contrast to its deterministic counterpart, the 𝑃/𝑃cr ratio of a stochastic laser beam is no longer an indicator of whether self-focusing will occur, but is, rather, a predictor of when the self-focusing is expected, in the sense of the first passage time, given the statistics of the laser field. We will also examine supercontinuum generation driven by stochastic laser pulses. The statistics of extreme bandwidths emerging from such a process is shown to converge, in the large-sample-size limit, to a generalized Poisson distribution whose mean is given by the exponent of the respective extreme-event statistics.