LPHYS'19.    Plenary Speakers:

  1. Generating High-Intensity Ultrashort Optical Pulses


    The sharp beams of laser light have given us new opportunities for deepening our knowledge about the world and shaping it. In 1985, the scheme for generation of ultrashort high-intensity laser pulses without destroying the amplifying material was created. First, the laser pulses were stretched in time to reduce their peak power, then amplified, and finally compressed. The intensity of the pulse then increases dramatically. Chirped pulse amplification paved the way to enhance the observation of multiphoton and tunnel ionization in gaseous media and other nonlinear effects such as filamentation, attosecond science, petawatt lasers development, etc.

  2. Many-Body Interactions of Cold Rydberg Atoms and Quantum Information

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      Igor I Ryabtsev

      Rzhanov Institute of Semiconductor Physics, Siberian Branch of the Russian Academy of Sciences, Novosibirsk, Russia

    Strong long-range interactions between highly excited Rydberg atoms form the basis for quantum information processing with neutral trapped atoms [1]. Entangled states can be generated using a temporary excitation of ground-state atoms to a strongly interacting Rydberg state. In this report, we will present our related experimental results on long-range many-body interactions between cold Rb Rydberg atoms in a magneto-optical trap, as well as our theoretical results on quantum information processing with Rydberg atoms.

    In the experiments with cold Rb atoms, we have observed for the first time a resonant dipole-dipole interaction (Stark-tuned Förster resonance) between two cold Rb Rydberg atoms confined to a small laser excitation volume [2]. We also observed radio-frequency-assisted Förster resonances in a few cold Rb Rydberg atoms which cannot be tuned by dc electric field [3,4]. This method can be applied to enhance the interactions of almost arbitrary Rydberg atoms with large principal quantum numbers. Some exotic quantum simulations demand to control the interactions of simultaneously three atoms. Three-body Förster resonances at long-range interactions of Rydberg atoms were first predicted and observed in Cs Rydberg atoms [5]. In these resonances, one of the atoms carries away an energy excess preventing the two-body resonance, leading thus to a Borromean type of Förster energy transfer. We have recently observed the three-body Förster resonances for a few Rb Rydberg atoms [6]. As the observed three-body resonances appear at the different dc electric field with respect to the two-body resonance, they represent an effective three-body operator, which can be used to directly control the three-body interactions in quantum gates with Rydberg atoms.

    We also proposed a novel scheme of deterministic single-atom excitation in mesoscopic ensembles based on the adiabatic passage and Rydberg blockade [7] theoretically, developed schemes of quantum gates with mesoscopic ensembles containing random number of atoms [8-10], tomography of quantum gates based on Rydberg atoms [11], schemes of quantum gates based on the adiabatic passage of the Stark-tuned Förster resonances [12,13] and three-qubit Toffoli gate [14,15].

    This work was supported by the RFBR Grants No. 17-02-00987 and 19-52-15010, the Russian Science Foundation Grants No. 16-12-00028 (for theoretical analysis) and No. 18-12-00313 (for laser excitation of Rydberg states), the public Grant CYRAQS from Labex PALM (ANR-10-LABX-0039), the EU H2020 FET Proactive project RySQ (Grant No. 640378), ARL-CDQI program through Cooperative Agreement No. W911NF-15-2-0061 and NSF Award No. 1720220.

    1. [1] I I Ryabtsev, I I Beterov, D B Tretyakov, V M Entin and E A Yakshina, Phys. Usp. 59, 196 (2016)
    2. [2] I I Ryabtsev, D B Tretyakov, I I Beterov and V M Entin, Phys. Rev. Lett. 104, 073003 (2010)
    3. [3] D B Tretyakov, V M Entin, E A Yakshina, I I Beterov, C Andreeva, and I I Ryabtsev, Phys. Rev. A 90, 041403(R) (2014)
    4. [4] E A Yakshina, D B Tretyakov, I I Beterov, V M Entin, C Andreeva, A Cinins, A Markovski, Z Iftikhar, A Ekers and I I RyabtsevPhys. Rev. A 94, 043417 (2016)
    5. [5] R Faoro, B Pelle, A Zuliani, P Cheinet, E Arimondo and P Pillet, Nat. Commun. 6, 8173 (2015)
    6. [6] D B Tretyakov, I I Beterov, E A Yakshina, V M Entin, I I Ryabtsev, P Cheinet and P Pillet, Phys. Rev. Lett. 119, 173402 (2017)
    7. [7] I I Beterov, D B Tretyakov, V M Entin, E A Yakshina, I I Ryabtsev, C MacCormick and S Bergamini, Phys. Rev. A 84, 023413 (2011)
    8. [8] I I Beterov, M Saffman, E A Yakshina, V P Zhukov, D B Tretyakov, V M Entin, I I Ryabtsev, C W Mansell, C MacCormick, S Bergamini and M P Fedoruk, Phys. Rev. A 88, 010303(R) (2013)
    9. [9] I I Beterov, M Saffman, V P Zhukov, D B Tretyakov, V M Entin, E A Yakshina, I I Ryabtsev, C W Mansell, C MacCormick, S Bergamini and M P Fedoruk, Laser Phys. 24, 074013 (2014)
    10. [10] I I Beterov, D B Tret'yakov, V M Entin, E A Yakshina, G N Khamzina and I I Ryabtsev, Quantum Electron. 47, 455 (2017)
    11. [11] I I Beterov, M Saffman, E A Yakshina, D B Tretyakov, V M Entin, G N Hamzina and I I Ryabtsev, J. Phys. B 49, 114007 (2016)
    12. [12] I I Beterov, M Saffman, E A Yakshina, D B Tretyakov, V M Entin, S. Bergamini, E A Kuznetsova and I I Ryabtsev, Phys. Rev. A 94, 062307 (2016)
    13. [13] I I Beterov, G N Hamzina, E A Yakshina, D B Tretyakov, V M Entin and I I Ryabtsev, Phys. Rev. A 97, 032701 (2018)
    14. [14] I I Ryabtsev, I I Beterov, D B Tretyakov, E A Yakshina, V M Entin, P Cheinet and P Pillet, Phys. Rev. A 98, 052703 (2018)
    15. [15] I I Beterov, I N Ashkarin, E A Yakshina, D B Tretyakov, V M Entin, I I Ryabtsev, P Cheinet, P Pillet and M Saffman, Phys. Rev. A 98, 042704 (2018)
  3. Challenges in the Damping of Sound in Superfluids


    Any homogeneous superfluid, provided that it involves short-range interactions, has an acoustic collective excitation branch, that is with a linear start at low wavenumber q. The corresponding quanta are bosonic quasi-particles, phonons. Due to phonon interactions, the sound is damped as it propagates in the superfluid, but at what rate?

    This fundamental problem has been little explored when the branch is concave at low q. At low temperatures, the usual three-phonon Beliaev-Landau damping mechanism no longer holds, because it does not conserve energy-momentum, and it is necessary to invoke the effective four-phonon interactions proposed by Landau and Khalatnikov in 1949 [1]. By taking up the study, we have been led to correct their results, limited to q small or large compared to the typical thermal wavenumber, and to generalize them by obtaining an original expression for the damping rate at intermediate wave numbers [2,3,4].

    Two main classes of systems would give a definitive experimental answer to the question, the cold fermionic atomic gases on the BCS side and the high pressure liquid helium 4. However, unwanted damping effects due to the interaction of phonons with thermally broken pairs of fermions or with rotons, which are not automatically negligible in these systems, have to be taken into account. We had also, there, to complete their theoretical treatment [5].

    1. [1] L Landau and I Khalatnikov, Zh. Eksp. Teor. Fiz. 19, 637 (1949)
    2. [2] H Kurkjian, Y Castin and A Sinatra, EPL - Europys. Lett. 116, 40002 (2016)
    3. [3] H Kurkjian, Y Castin and A Sinatra, Ann. Phys. 529, 1600352 (2017)
    4. [4] Y Castin, Compt. Rendus Phys., in press
    5. [5] Y Castin, A Sinatra and H Kurkjian, Phys. Rev. Lett. 119, 260402 (2017)
  4. Science at XFELs: Present Status and Future Directions


    X-ray Free Electron Lasers (XFELs) deliver coherent X-ray pulses, combining unprecedented power densities of up to 1020 W/cm2 and extremely short pulse durations down to hundreds of attoseconds. Such intense XFEL pulses make single-shot diffraction of nanometer-sized objects, tiny protein crystals, and non-crystalized biomolecules a tangible reality. Such ultrashort XFEL pulses allow us also to visualise temporal variations of charge and structure in femto- to attoseconds time scales, which may occur upon photoexcitation/photoionisation in any form of matter. Also, since the XFEL pulses give access to a new regime of X-ray intensities, they open new venues in studying the interaction between intense X-rays and various forms of matter. Understanding the ultrafast reactions induced by the XFEL pulses is of fundamental interest, as well as of crucial importance, for XFEL applications. The present talk will sketch the current status of science studied with XFELs and describe its future directions, referring to the recent developments at various facilities.