Junior Quantum Seminar

Please join us for the Junior Quantum Seminar with Michael A. Eichenberger from the Laboratory of Quantum Gases (LQG) at EPFL who will give the talk "Towards programmable all-to-all interactions of ultracold fermions in a cavity-QED system" and Filippo Ferrari from the Laboratory of Theoretical Physics of Nanosystems (LTPN) at EPFL who will give the talk "Dissipative quantum chaos: foundation and relevance for quantum technologies" on Tuesday December 17th from 9h30-11h.

PLEASE NOTE: The Junior Quantum Series are for gathering  the junior quantum community of master's students, PhDs and post-docs at EPFL, to create a non-judgmental space were scientific ideas can be shared between peers. This event is not for Professors or senior researchers. 

ABSTRACT:
1.Towards programmable all-to-all interactions of ultracold fermions in a cavity-QED: Cavity quantum electrodynamics (cavity QED) studies the interaction between atoms and the light confined in an optical resonator. These interactions are characterized by strong coupling between single atoms and single photons, and by the emergence of cavity-mediated atomic long-range interactions, which have enabled various quantum technological tasks, from quantum-enhanced metrology to quantum simulation of strongly correlated matter.  
While the natively emerging systems already offer a rich phenomenology, they are limited by the symmetrical structure of the collective coupling. To achieve programmability beyond this, local control over the atom-light interaction is required. One possible approach to this is the integration of a high-resolution microscope into the system, allowing for local engineering of the atom level structure through use of additional optical fields. With this, more elaborate interaction geometries and disordered models such as spin glasses and holographic models like the Sachdev-Ye-Kitaev model become realizable. In this talk, I will give a general introduction on the building blocks of cavity QED resulting in all-to-all interactions and discuss our experimental approach and apparatus to add programmability. Finally, I will discuss our advances towards programmable quantum simulations with interacting fermions.  
2.Dissipative quantum chaos: foundation and relevance for quantum technologies: The study of chaos and integrability in open quantum many-body systems is central in many research areas, from high-energy physics to quantum optics, from quantum technologies to condensed matter. To date, dissipative quantum chaos is understood on the basis of the universal predictions of non-Hermitian random matrix theory: in presence of chaos, the generator of the dissipative dynamics (the so-called Liouvillian superoperator) behaves as a large random matrix. In this talk, I introduce a novel definition of dissipative quantum chaos that allows explaining physical phenomena that would otherwise remain elusive, including recent experimental findings. An open quantum system exhibits chaotic behavior if its Liouvillian spectral structure is described by random matrix theory and if this structure significantly impacts individual stochastic realizations of the dynamics, commonly referred to as quantum trajectories. I discuss several applications following from this theoretical framework. First, I consider the driven-dissipative Bose-Hubbard model, a paradigmatic system for studying interacting quantum fluids of light. I clarify the interplay of integrability and chaos across its phase diagram, paving the way for the experimental observation of dissipative quantum chaos in, e.g., superconducting-based quantum simulators. A recent experimental application concerns the transition from integrability to dissipative chaos in an open Floquet bosonic system. I extend the discussion to chains of coupled nonlinear driven-dissipative oscillators, where many-body effects lead to regular and chaotic dynamics. Second, I focus on the dispersive readout of a transmon qubit, showing how dissipative quantum chaos can emerge in the circuit quantum electrodynamics architecture underlying the qubit’s readout, enhancing or destroying the instrument’s performance. Generally speaking, further study is warranted to understand in a more systematic way how dissipative chaos can affect the performance of quantum computing devices. 

BIO:
1.Michael A. Eichenberger: Michael A. Eichenberger is a PhD student at the Laboratory of Quantum Gases (LQG) at EPFL, where he is working on an experiment exploring cavity-mediated interactions in systems of ultracold fermionic gases, focusing on achieving quantum simulation of disordered fermionic systems. Michael did an apprenticeship as a laboratory technician at PSI and obtained both his bachelor's and master’s degree at ETH Zürich. He carried out his master thesis at MPQ in Munich, where he investigated the creation of optical cat-states through Rydberg-blockade in optical resonators. Besides atoms, he really loves Music.  
2.Filippo Ferrari: Filippo Ferrari is a PhD student from LTPN lab headed by Professor Vincenzo Savona. His current research focuses on emergent phenomena in open quantum many-body systems.