|14:00 to 15:00||Matthias Weidemuller (Heidelberg University, Germany)||
Taming Atomic Giants: How Rydberg atoms became veritable Quantum Simulators
Due to their exaggerated properties, highly excited (Rydberg) atoms have attracted physicists for more than a century, and the study of these atomic giants is intimately connected to major advances in modern quantum theory. In the last years, a new aspect was added to this everlasting fascination. Forces between Rydberg atoms are huge causing measurable effects over macroscopic distances in the micrometer range. As an important feature, these dipolar interactions can not only be tuned in strength, but also in their characteristic dependence on the distance between the atoms. Such control, in combination with modern methods of laser cooling and trapping, opens exciting perspectives for using Rydberg atoms as simulators for quantum many-body systems in order to address fundamental problems as, e.g., the emergence of magnetism in condensed matter or energy transport in photosynthetic complexes. In fact, it was first thought that the fragility of Rydberg atoms (the electron’s binding energy is only a few millielectronvolts or below) would impede meaningful applications. Yet, recent advances in quantum engineering have promoted Rydberg atoms to one of the hottest candidates for large-scale quantum simulation.
|15:00 to 15:40||J Hecker Denschlag (University of Ulm, Germany)||
Life and death of a cold BaRb+ molecule inside an ultracold cloud of Rb atoms
We study the evolution of a cold single BaRb+ molecule while it continuously collides with ultracold Rb atoms. The initially weakly bound molecule can undergo a sequence of elastic, inelastic, reactive, and radiative processes. We investigate these processes by developing methods for discriminating between different ion species, electronic states, and kinetic ion energy ranges. By analyzing the experimental data while taking into account theoretical insights, we obtain a consistent description of the typical trajectory through the manifold of available atomic and molecular states. Monte Carlo simulations describe the measured dynamics well.
|15:40 to 16:20||Rene Gerritsma (University of Amsterdam, Netherlands)||
The quantum physics of interacting atoms and ions
In recent years, a novel field of physics and chemistry has developed in which trapped ions and ultracold atomic gases are made to interact with each other. These systems find applications in studying quantum chemistry and collisions , and a number of quantum applications are envisioned such as ultracold buffergas cooling of trapped ions and quantum simulation of fermion-phonon coupling .
In our experiment, we overlap a cloud of ultracold 6Li atoms in a dipole trap with a 171Yb+ ion in a Paul trap. The large mass ratio of this combination allows us to suppress trap-induced heating . For the first time, we buffer gas-cooled a single Yb+ ion to temperatures close to the quantum (or s-wave) limit for 6Li-Yb+ collisions. We study the temperature dependence of the spin exchange rates in these collisions and compare to theory to find estimates for the atom-ion scattering lengths. Our results open up the possibility to study trapped atom-ion mixtures in the quantum regime and to study ions interacting with weakly bound atomic Feshbach dimers . Moreover, Feshbach resonances are predicted to exist between the atoms and ions that can be explored at the ultracold temperatures acquired in our lab. Finally, I will discuss strategies and prospects for reaching deeper into the quantum regime.
 M Tomza et al., Rev. Mod. Phys. 91, 035001 (2019).
 U. Bissbort et al., Phys. Rev. Lett. 111, 080501 (2013).
 M. Cetina et al., Phys. Rev. Lett. 109, 253201 (2012).
 H. Hirzler et al., Phys. Rev. Research 2, 033232 (2020).
 T. Secker et al., Phys. Rev. Lett. 118, 263201 (2017).
 N. Ewald et al., Phys. Rev. Lett. 122, 253401 (2019).
|16:20 to 17:00||Jesus Perez Rios (Fritz Haber Institute of the Max Planck Society, Germany)||
Few-body processes in cold chemistry
In this talk, we present a few-body approach to the physics of a charged impurity in an ultracold bath. We study how the nature of the bath affects the dynamics and evolution of the charged impurity due to cold chemical reactions: atom-atom-ion three-body recombination and molecular ion formation after ion-molecule collisions. In particular, we find that the nature of the charged impurity is readily controlled by tuning the binding energy of the ultracold molecular bath. Consequently, one finds the first principle explanation to some of the relevant parameters required to characterize the impurity's many-body evolution. In addition, we present our findings on the formation of van der Waals molecules on a buffer gas cell through three-body recombination, showing that almost any atom X in a buffer gas cell in the presence of He will lead to the formation of HeX van der Waals molecules.
|19:00 to 19:50||Robin Kaiser (Université Côte d’Azur, CNRS, France)||
Resonant dipole-dipole interactions: Dicke subradiance and Anderson localisation
The quest for Anderson localization of light is at the center of many experimental and theoretical activities. Cold atoms have emerged as interesting quantum system to study coherent transport properties of light. Initial experiments have established that dilute samples with large optical thickness allow studying weak localization of light, which has been well described by a mesoscopic model. Recent experiments on light scattering with cold atoms have shown that Dicke super- or subradiance occurs in the same samples, a feature not captured by the traditional mesoscopic models. The use of a long range microscopic coupled dipole model allows to capture both the mesoscopic features of light scattering and Dicke super- and subradiance in the single photon limit. I will review experimental and theoretical state of the art on the possibility of Anderson localization of light by cold atoms.
|19:50 to 20:40||Yong P Chen (Purdue University, USA)||
“Atomtronic Spintronics”: from Quantum Chemistry to Quantum Transport
I will review and describe our experiments studying and controlling spin-dependent quantum chemistry and quantum transport in an atomic ( 87 Rb) Bose-Einstein condensate (BEC), where different spin states can be addressed and coupled to induce “synthetic” spin-orbit coupling (SOC) and/or “synthetic dimensions”. We have demonstrated a new approach of quantum control of (photo) chemical reactions (photoassociation of molecules from atoms) --- which can be thought of a “quantum chemistry interferometry” --- by preparing reactants in (spin) quantum superposition states and interfering multiple reaction pathways . By performing a “quantum quench” in a SOC BEC, we induce head-on collisions between two spinor BECs (realizing a “condensate collider”) and study spin transport and how it is affected by SOC, revealing rich phenomena arising from the interplay between quantum interference and many-body interactions . By creating a “synthetic” cylinder with also synthetic magnetic fluxes, the BEC acquires an emergent crystalline order (in absence of an optical lattice) with a topological band structure featuring band crossings protected by nonsymmorphic symmetry, that we reveal by Bloch oscillations and can further control and manipulate . Our experimental system can be a rich playground to study physics of interests to AMO physics, quantum chemistry and condensed matter physics.
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|20:40 to 21:30||Kazi Rajibul Islam (University of Waterloo, Canada)||
Trapped ion quantum simulation: opportunities and challenges
Trapped ions are among the most advanced technology platforms for quantum information processing. When laser-cooled close to absolute zero temperature, atomic ions form a Coulomb crystal with micron-scale spacings in a radio-frequency ion trap. Qubit or spin-1/2 levels, encoded in hyperfine energy states of each ion, can be initialized, manipulated, and detected optically with high precision. Laser fields can also couple the qubit states of arbitrary pairs of ions through (virtual) excitation of collective phonon modes, creating programmable quantum logic operations and spin Hamiltonians. In this talk, I will focus on programmable trapped-ion quantum spin simulators for analog, digital, or analog-digital hybrid quantum simulation protocols. These devices can be beneficial to solve hard problems in areas as diverse as condensed matter physics and high-energy physics.