QSE Junior Quantum Seminar - Filippo Ferrari & Franco De Palma

Please join us for the Junior Quantum Seminar with Filippo Ferrari from the Laboratory of Theoretical Physics of Nanosystems (EPFL), who will give the talk "Dissipative quantum chaos: foundation and relevance for quantum technologies" and Franco De Palma from the Hybrid Quantum Circuits laboratory (EPFL) who will give the talk "Strong hole-photon coupling in planar Ge for probing charge degree and Wigner molecule states" on Tuesday March 11th 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. 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.
2. Semiconductor quantum dots (QDs) in planar germanium (Ge) heterostructures have emerged as front-runners for future hole-based quantum processors. Here, we present strong coupling between a hole charge qubit, defined in a double quantum dot (DQD) in planar Ge, and microwave photons in a high-impedance (Zr = 1.3 kΩ) resonator based on an array of superconducting quantum interference devices (SQUIDs). Our investigation reveals vacuum-Rabi splitting with coupling strengths up to g0/2π = 260 MHz, and a cooperativity of C ~ 100, dependent on DQD tuning. Furthermore, utilizing the frequency tunability of our resonator, we explore the quenched energy splitting associated with strong Coulomb correlation effects in Ge QDs. The observed enhanced coherence of the strongly correlated excited state signals the presence of distinct symmetries within related spin functions, serving as a precursor to the strong coupling between photons and spin-charge hybrid qubits in planar Ge. This work paves the way towards coherent quantum connections between remote hole qubits in planar Ge, required to scale up hole-based quantum processors.

1. 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.
2. Franco De Palma is a PhD student at the Hybrid Quantum Circuits Laboratory lead by Prof. Pasquale Scarlino, at EPFL. He got a bachelor’s degree in physics engineering at Politecnico di Torino and a master’s degree in Nanotechnologies for ICTs from a master program shared among Politecnico di Torino, INP Grenoble and EPFL. His research is focused on the integration of high-impedance superconducting resonators with semiconducting quantum dots on a planar Ge/SiGe heterostructure for long-range qubit connectivity, fast high-fidelity readout, analog quantum simulations and high-efficiency GHz photodetectors.