Tuesday 4:30 pm (Freiburg) / 7:30 am (Vancouver)

18.04.23 – Andrea Trabattoni, DESY Hamburg

25.04.23 – José Crespo López-Urrutia, MPI Heidelberg

02.05.23 – Sara Bonella, EPFL Lausanne, Switzerland

09.05.23 – Andreas Buchleitner „Good Scientific Practice

23.05.23 – Guillaume Salomon, University of Hamburg

06.06.23 – Jan Marcus Dahlström, Lund University, Sweden

13.06.23 – Christian Schäfer, Chalmers University of Technology, Göteborg, Sweden

27.06.23 – Krzysztof Jachymski, University of Warsaw, Poland

04.07.23 – Charles Bourassin, Université Paris-Saclay, France

11.07.23 – Marjan Mirahmadi, Fritz Haber Institute of the Max Planck Society, Berlin

18.07.23 – Pieter Claeys, MPI PKS Dresden

18.07.23 – Pieter Claeys, MPI PKS Dresden

Dual-unitary circuit dynamics

Dual-unitary circuits have recently emerged as a new model of exactly solvable yet chaotic many-body dynamics. After a short introduction to dual-unitary circuit dynamics and their underlying space-time duality, I will discuss two examples where the connection with random matrix theory and aspects of quantum chaos can be made analytically. First I will discuss operator spreading, showing exact results for dual-unitary circuits and arguing that dual-unitary circuits can serve as a useful starting point to describe the (more generic) dynamics of unitary circuits away from dual-unitarity. Second, I will discuss the notion of emergent quantum state designs and ‚deep thermalization‘ in dual-unitary circuits, where dual-unitary dynamics followed by projective measurements on a bath gives rise to an ensemble of states that becomes indistinguishable from the uniform Haar-random ensemble after a sufficiently long time.

Chair: Andreas Buchleitner

11.07.23 – Marjan Mirahmadi, Fritz Haber Institute of the Max Planck Society, Berlin

Three-body recombination processes: Examples in AMO physics

Three-body recombination or ternary association is a termolecular reaction in which three particles collide to form a bound state between two of them as a product state. This process plays an important role in many areas of physics and chemistry, determining the stability of quantum gases, the formation of new charged products in hybrid atom-ion traps, the formation of van der Waals molecules as well as in various reactions in plasma physics, astrophysics, and atmospheric physics.

In the main part of my talk, I will discuss the ion-atom-atom three-body reaction A+A+B+ at collision energies ranging from 100 µK to 105 K, concentrating on the formation of either molecules or molecular ions. The dynamics is treated via a direct three-body formalism based on the classical trajectory method in hyperspherical coordinates [1,2]. As a result, the validity range for the previously derived threshold law for charged-neutral-neutral reactions is established [2].

In the second part of my talk, I will briefly discuss ozone formation in a direct (without invoking the existence of an intermediate complex) three-body recombination reaction O2+O+M→O3+M. I will provide the full ab initio pressure-independent rate for ozone formation derived for temperatures 50-900 K. A good agreement with available experimental data for temperatures 100-900 K is obtained by accounting for the process of vibrational quenching of the nascent population [3].

[1] J. Pérez-Ríos, S. Ragole, J. Wang, and C. H. Greene, J. Chem. Phys. 140, 044307 (2014).

[2] M. Mirahmadi, J. Pérez-Ríos, J. Chem. Phys. 158, 024103 (2023).

[3] M. Mirahmadi, J. Pérez-Ríos, O. Egorov, V. Tyuterev, and V. Kokoouline, Phys. Rev. Lett. 128, 108501 (2022).

Chair: Katrin Erath-Dulitz

04.07.23 – Charles Bourassin, University Paris-Saclay, France

Quantum state tomography, decoherence and entanglement in attosecond photoionisation

Until the late 80s, the possibility of accessing the complete quantum state of a system, that is measuring its density matrix, was considered out-of-reach or even metaphysical. This changed with the emergence of the concept of Quantum State Tomography. Now widely used in domains such as quantum optics, or cold atom physics, this approach has allowed fundamental tests of quantum mechanics and of decoherence theory and has contributed to establishing entanglement as a resource for quantum technologies.

Since its birth in 2001, attosecond science has allowed the study of ultrafast processes in matter, such as photoionization, mostly by the use of electron interferometric techniques. Paradoxically, although based on interferometry, i.e. the textbook case to underline the importance of coherence, the question of quantum coherence has been largely kept quiet in attosecond photoionization. Such a simplification may have contributed to miss part of the complexity of the ionization process.

In this seminar, we will see how historical attosecond metrology techniques can be reinterpreted under the scope of quantum state tomography, and how this will allow one to explore the role of decoherence and entanglement in attosecond ionisation processes.

Chair: Giuseppe Sansone

27.06.23 – Krzysztof Jachymski, University of Warsaw, Poland

Hybrid quantum systems

Quantum simulators can be a valuable tool in modern day technology. Ultracold atoms are among the most prominent systems which can be utilized for this task. Hybrid systems consisting of more than one species are challenging to control and inherently more complex, but at the same time can be regarded as quite natural analogue quantum simulators. In particular, ion-atom systems display unique properties due to their relatively strong and long-ranged interactions. I will discuss the basic properties of such systems and show how strong coupling polaron phenomena can be simulated with their help.

Chair: Tobias Schätz

13.06.23 – Christian Schäfer, Chalmers University of Technology, Göteborg, Sweden

Ab initio QED: Correlated light-matter states from first principles and their use for spectroscopy, chirality, and chemistry

The alchemical dream of altering a given material on demand is at the heart of chemistry and material science.
Confining optical or plasmonic modes results in a strong increase in light-matter coupling and leads to the creation of hybrid light-matter states. Control over the electromagnetic confinement allows, therefore, to non-intrusively control the correlated eigenstates, resulting in modified material dynamics, and its chemistry. We will start with a brief introduction to the emergent field of ab initio QED [1,7], illustrating an intuitive shortcut for the description of self-consistent light-matter interaction [2]. We will subsequently investigate how chemical reactions can be controlled, shining light on the microscopic mechanism behind vibrational strong coupling [3,4,7]. Lastly, we discuss the consequences of breaking chiral symmetry with specifically designed electromagnetic environments, which paves the way for a new direction in chiral recognition [5,6,7].

[1] C. Schäfer, F. Buchholz, M. Penz, M. Ruggenthaler, and A. Rubio, PNAS 2021 Vol. 118 No. 41 e2110464118.
[2] C. Schäfer and G. Johansson, PRL 128, 156402, (2022).
[3] C. Schäfer, J. Flick, E. Ronca, P. Narang, and A. Rubio, Nature Communications, (2022) 13:7817.
[4] C. Schäfer, Phys. Chem. Lett. 2022, 13, 30, 6905-6911.
[5] C. Schäfer, D. Baranov, J. Phys. Chem. Lett. 2023, 14, 15, 3777-3784.
[6] D. Baranov, C. Schäfer, M. Gorkunov arXiv:2212.13090, accepted in ACS Photonics.
[7] In progress.

Chair: Dominik Lentrodt / Andreas Buchleitner

06.06.23 – Jan Marcus Dahlström, Lund University, Sweden

Rabi oscillations and dressed-atom stabilization at XUV wavelengths

Two-level atoms can “Rabi flop” with periodic modulations of populations over time. Recently, the development of seeded Free-Electron Lasers (FEL) with intense light (~1013 W/cm2) at short wavelengths (~20 eV) have made it possible the observe ultrafast Rabi dynamics in helium atoms [1]. The measured photoelectron signal revealed an Autler–Townes (AT) doublet and an avoided crossing, phenomena that are fundamental in coupled atom–field physics. Interactions with extreme fields require a description of electron dynamics beyond the two-level atom, due to non-linear photoionization losses and polarization effects [2]. We have performed numerical simulations, using the Time-Dependent Configuration-Interaction Singles method (TDCIS) [3], with infinite-time surface flux methods (iSURF) [4] to obtain realistic photoelectron spectra from Rabi-flopping He atoms. We show that the ultrafast build-up of the AT doublet carries a signature of a non-linear quantum interference pathways, see Fig.1. With further exploration of XUV Rabi dynamics, in a broader range of parameters, we show that dressed-atom stabilization is possible for circularly polarized FEL fields [5].

[1] Nandi, S., Olofsson, E., Bertolino, M. et al. Observation of Rabi dynamics with a short-wavelength free-electron laser. Nature 608, 488–493 (2022). https://doi.org/10.1038/s41586-022-04948-y

[2] Beers, B. L., Armstrong, Jr. L. Phys. Rev. A 12 2447 (1975)

[3] Greenman, L. et al. Phys. Rev. A 82, 023406 (2010)

[4] Morales, F. et al J. Phys. B: At. Mol. Opt. Phys. 49 245001 (2016)

[5] arXiv:2305.07363 [physics.atom-ph]

Chair: Giuseppe Sansone

23.05.23 – Guillaume Salomon, University of Hamburg

Exploring strongly correlated quantum systems at the single particle level

The manipulation and detection of quantum many-body systems down to the level of single particle and spin offer a totally new paradigm to study strongly correlated phases.

In particular, spin-resolved quantum gas microscopy allows to directly measure arbitrary N-point correlations involving both spin and density which opens fascinating perspectives for experiments.

I will discuss here recent equilibrium and out of equilibrium experimental studies of the Fermi-Hubbard model realised by trapping ultracold fermions in optical lattices, focusing on the interplay between doping and magnetism.

Fundamental differences between doped one- and two-dimensional Mott insulators will be presented based on the observation of spin-charge separation signatures in 1d, magnetic polarons and Fermi-liquid in 2d.

I will finally discuss our current efforts to develop a novel quantum simulator with which we will investigate the SU(N) Fermi-Hubbard model and topological phases.

Find more information

Chair: Andreas Buchleitner

09.05.23 – Andreas Buchleitner „Good Scientific Practice

02.05.23 – Sara Bonella, EPFL Lausanne, Switzerland

Welcome to the MaZe, a new approach for simulating adiabatic systems

In several domains of physics, the minimization of an energy function with respect to a set of auxiliary variables must be performed to define the dynamics of physical degrees of freedom. A prototypical example is first principles (a.k.a. Born-Oppenheimer) dynamics in which nuclear degrees of freedom move in an energy landscape in which electrons have relaxed to the minimum of their ground state energy.

Existing methods to simulate these systems (including direct minimization and Car-Parrinello dynamics) suffer from limitations. In this talk, a recent and effective formalism to simulate this type of systems will be discussed: the Mass-Zero (MaZe) Constrained Dynamics [1]. In MaZe the minimum condition is imposed as a constraint on the auxiliary variables treated as degrees of freedom of zero inertia driven by the physical system. The method is formulated in the Lagrangian framework, enabling the properties of the approach to emerge naturally from a fully consistent dynamical and statistical viewpoint [2].

Several examples of current uses of MaZe will be presented, including first principles molecular dynamics based on orbital-free density functional theory [3] and classical polarizable models [4]. A recent development enabling to study ionic transport for classical polarizable systems in the presence of an external magnetic field will also be discussed [5]. These example indicate that the method is numerically efficient and stable.

[1] A. Coretti, S. Bonella, G. Ciccotti, „Constrained molecular dynamics for polarizable models“, The Journal of Chemical Physics Communications149 (2018) 191102

[2] S. Bonella, A. Coretti, R. Vuilleumier, G. Ciccotti, „Adiabatic motion and statistical mechanics via mass-zero constrained dynamics“, PCCP22 (2020) 10775

[3] A. Coretti, T. Baird, R. Vuilleumier, and S. Bonella, „Mass-zero constrained dynamics for simulations based on orbital-free density functional theory „, The Journal of Chemical Physics157 (2022) 214110

[4] A. Coretti , L. Scalfi , C. Bacon , B. Rotenberg , R. Vuilleumier , G. Ciccotti , M. Salanne , and S. Bonella, „Mass-zero constrained molecular dynamics for electrode charges in simulations of electrochemical systems“, The Journal of Chemical Physics152 (2020) 194701

[5] D. Girardier, A. Coretti, G. Ciccotti, S. Bonella „Mass-Zero constrained dynamics and statistics for the shell model in magnetic field“, The European Physical Journal B, 94 (2021) art. N. 158

Chair: Tanja Schilling

25.04.23 – José Crespo López-Urrutia, MPI Heidelberg

Cold and ultra-cold highly charged ions for clock applications and New Physics searches

Using the ionic charge as an additional degree of freedom does not only enlarge the size of the periodic table in a further dimension, but also lets qualitatively new possibilities appear. Forbidden transitions that appear at high photon energies are a very important outcome. Frequency metrology with optical clocks [1] has become a key tool for novel fundamental physics studies [2] using atomic systems. Its outstanding resolution, reproducibility and accuracy makes it in principle capable of sensing the effect of all Standard Model interactions on the frequency of electronic transitions, such as, e. g., a variation of the fine-structure constant [3]. For this purposes, highly charged ions have to be cooled down to the microkelvin regime. Furthermore, disentangling the different sources of the underlying modifications of the electronic wave function is thereby crucial. For this, it is necessary to change the neutron number as well as the overlap of the electronic wave function with that of the nucleus in a well-defined way, as in the generalized King-plot method [4]. Isoelectronic and isonuclear sequences of highly charged ions (HCI) offer a plethora of possibilities in this regard [5], since they possess many different types of exceptionally long-lived metastable states up to x-ray energies. The developments [6-8] leading to an optical clock based on HCI [9] show the promise from an extension of frequency metrology beyond the optical range. For this purpose, we are preparing an experiment combining an extreme-ultraviolet frequency comb based on high-harmonic-generation [10] with a superconducting radio-frequency trap [11]. 

  • [1] Yudin, V. I., Taichenachev, A. V. & Derevianko, A., Phys. Rev. Lett. 113, 233003 (2014)
  • [2] Safronova, M. S. et al., Rev. Mod. Phys. 90, 025008 (2018)
  • Schiller, S., Phys. Rev. Lett. 98, 180801 (2007)
  • [3] Berengut, J., Dzuba, V. & Flambaum, V., Phys. Rev. Lett. 105, 120801 (2010).
  • [4] Berengut, J. C., Delaunay, C., Geddes, A. & Soreq, Y., Phys. Rev. Res. 2, 043444 (2020)
  • [5] Kozlov, M. G., Safronova, M. S., Crespo López-Urrutia, J. R. & Schmidt, P. O., Rev. Mod. Phys. 90, 045005 (2018)
  • [6] Schmöger, L., et al., Science 347, 1233 (2015)
  • [7] Micke, P., et al., Nature 578, 60 (2020)
  • [8] King, S. A., et al., Phys. Rev. X 11, 041049 (2021)
  • [9] King, S.A., et al. Nature 611, 43 (2022)
  • [10] Nauta, J. et al., Opt. Express 29, 2624 (2021)
  • [11] Stark J. et al., Rev. Sci. Instrum. 92, 083203 (2021)

Chair: Bernd von Issendorff

18.04.23 – Andrea Trabattoni, DESY Hamburg

New advances in the investigation of ultrafast molecular dynamics

Imaging the microscopic world in real space and real time is a grand challenge of science. In this context, the landscape of techniques to image ultrafast molecular dynamics is vast, including powerful methods such as lightwave-driven scanning tunnelling microscopy or ultrafast electron diffraction [1,2]. In this seminar, the main methods and results in the field of ultrafast molecular physics will be presented, with a particular emphasis on strong-field-based techniques [3] such as laser-induced electron diffraction (LIED) [4]. Possible perspectives toward the future advancement of ultrafast molecular imaging will be discussed.
[1] Science 302, 1382–1385 (2003).
[2] Nature 585, 58–62 (2020).
[3] Nat. Comm. 11, 2546 (2020).
[4] Nature 483, 194 (2012).

For further information

Chair: Lukas Bruder