Talks
Upcoming
Prof. Benedetta Flebus
(Boston College)
13 December 2023 at 15:00 CET
Title:
Non-Hermitian physics in magnetic systems
Abstract:
While magnetic systems have been extensively studied both from a fundamental physics perspective and as building blocks for a variety of applications, their topological properties, however, remain relatively unexplored due to their inherently dissipative nature. I will start this talk by discussing how the recent introduction of non-Hermitian topological classifications has opened up opportunities for engineering topological phases in magnetic systems, and I will present our first proposal of a non-Hermitian topological magnonic system, i.e., a realization of an SSH non-Hermitian model via a one-dimensional spin-torque oscillator array.Then I will discuss the conditions under which magnetic insulating systems can host one of the most striking non-Hermitian phenomena with no Hermitian counterpart, i.e., the skin effect, which underlies the breakdown of the bulk-edge correspondence.
Previous
Prof. Jan Wiersig
(Otto von Guerricke Universität Magdeburg)
6 December 2023 at 15:00 CET
Title:
Non-Hermitian optics in microcavities: from exceptional points to exceptional sensors
Abstract:
Optical microresonators play a fundamental role in many fields of basic and applied research in physics. Due to optical losses, such as absorption and radiation, these resonators are open systems. In the last years, a new research field, non-Hermitian optics, has emerged, which focuses on the interesting and usable aspects of these losses. It has been shown that the effects are strongly enhanced near so-called non-Hermitian degeneracies at exceptional points in parameter space. These unconventional degeneracies, at which not only the resonant frequencies but also the corresponding optical modes coalesce, are highly sensitive to perturbations. One possible application are therefore ultra-sensitive sensors. In this talk I will discuss some mechanisms to create exceptional points in optical whispering-gallery cavities. Moreover, I will introduce a new concept to quantify the response of open systems at exceptional points.
Prof. Benjamin Stickler
(Ulm University)
22 November 2023 at 15:00 CET
Title:
Non-reciprocal interactions and entanglement between optically levitated nanoparticles
Abstract:
Optically levitating dielectric nanoparticles in ultra-high vacuum, where their motion can be cooled into the deep quantum regime, provides a promising platform for force and torque sensing and for high-mass tests of quantum physics. In this talk I will discuss recent results on the coupled dynamics of co-levitated nanoparticles interacting via optical binding and via electrostatic forces. I will show how non-reciprocal interactions [1] and mechanical entanglement [2] between two particles can be generated and observed by controlling the light fields suspending them.
[1] Rieser, Ciampini, Rudolph, Kiesel, Hornberger, Stickler, Aspelmeyer, and Delić, Science 377, 987 (2022).
[2] Rudolph, Delić, Aspelmeyer, Hornberger, and Stickler, Phys. Rev. Lett. 129, 193602 (2022).
YouTube link:
https://www.youtube.com/watch?v=0b4IBY69pJM
Prof. Kater Murch
(Washington University)
8 November 2023 at 15:00 CET
Title:
On the interplay of energy, dynamics, memory, and thermodynamics - experiments on quantum measurement and dissipation at microwave frequencies
Abstract:
Josephson junction based quantum circuits have enabled broad exploration into open quantum systems in the microwave frequency domain. The combination of coherent quantum bits, robust single qubit control, and quantum noise limited parametric amplifiers has yielded an unprecedented view into the physics of quantum measurement and quantum dissipation. My group's research focuses on research topics that touch on fundamental questions including weak measurement and quantum trajectories, non-Markovian dynamics, effective non-Hermitian dynamics, quantum thermodynamics, and quantum sensing. In this talk, I will introduce the experimental architecture that forms the basis for this work, and then focus specifically on ongoing experiments where we study effective non-Hermitian dynamics in a dissipative qubit, and how this reveals fundamental aspects about the interplay between energy and dynamics in quantum systems.
YouTube link:
https://www.youtube.com/watch?v=NZUW_Tjkh00
Prof. Henning Schomerus
(Lancaster University)
25 October 2023 at 15:00 CET
Title:
Active and passive non-Hermitian devices
Abstract:
In photonic systems, gain and loss can be used to induce intriguing effects that are linked to non-Hermitian and topological physics. Prominent examples are exceptional points and the non-Hermitian skin effect, which can be used for enhanced sensing and directed amplification, as well as symmetry-protected states, which can be addressed by topological mode selection. Many of these applications make explicit use of mode nonorthogonality, which becomes especially intriguing when the system is nonreciprocal. I describe how these effects can be probed in response theory, transport, and scattering, and highlight fundamental practical limits of the observability of some effects.
YouTube link:
https://www.youtube.com/watch?v=7i4eBg4WdW8
Dr. Angelo Carollo
19 July 2023 at 15:00 CEST
Title:
Exotic effects and topology in Hermitian and non-Hermitian Waveguide QED
Abstract:
As light can mediate interactions between atoms in a photonic environment, engineering it for endowing the photon-mediated Hamiltonian with desired features is crucial in quantum research.
In the first part of the talk I will discuss exotic properties of interactions mediated by non-Hermitian reservoirs, made of lossy photonic lattices. I will show in a paradigmatic case study that when these losses are suitably structured, exotic emission properties can be observed. Photons can mediate dissipative, fully non-reciprocal, interactions between the emitters with range critically dependent on the loss rate. Counter-intuitively, this occurs irrespective of the lattice boundary conditions. Thus photons can mediate an effective emitters’ Hamiltonian which is translationally- invariant despite the fact that the field is not.
In the second part of the talk I will introduce general theorems on the topology of photon-mediated interactions in terms of both Hermitian and non-Hermitian topological invariants, unveiling the phenomena of topological preservation and reversal, and revealing a system-bath topological correspondence. Depending on the Hermiticity of the environment and the parity of the spatial dimension, the atomic and photonic topological invariants turn out to be equal or opposite. Consequently, the emergence of atomic and photonic topological boundary modes with opposite group velocity in two-dimensional Hermitian topological systems is established. Owing to its general applicability, these results can guide the design of Hermitian and Non-Hermitian topological systems.
YouTube link:
https://www.youtube.com/watch?v=6UvoIVyEy-o
Prof. Dr. J. Lado
28 June 2023 at 15:00 CEST
Title:
Static and dynamic topological modes in interacting non-Hermitian systems with tensor networks
Abstract:
The emergence of topological modes in non-Hermitian systems has established a new strategy to create quantum modes in open quantum systems. While formidable progress has been obtained in non-Hermitian topological systems in the single particle limit, the effect of many-body interactions remains an open problem in quantum physics. I will show that in an engineered platform based on quantum dots, non-Hermitian physics with tunable interactions can be engineered [1]. Using a non-Hermitian tensor network method, we demonstrate that topological modes in this platform remain all the way from the non-interacting to the fully interacting limit. Furthermore, I will show that dynamical interacting non-Hermitian modes can be visualized using a tensor-network kernel polynomial algorithm, allowing us to probe the many-body topology of strongly interacting non-Hermitian systems [2]. I will show that the local spectral functions computed with our algorithm reveal topological spin excitations in a non-Hermitian spin model, faithfully reflecting the non-trivial line gap topology in a many-body model even in the presence of the non-Hermitian skin effect. Our results demonstrate a tensor-network methodology to probe dynamical excitations in topological matter driven by the interplay of many-body interactions and non-Hermiticity.
[1] Timo Hyart and J. L. Lado, Phys. Rev. Research 4, L012006 (2022)
[2] Guangze Chen, Fei Song, Jose L. Lado, Phys. Rev. Lett. 130, 100401 (2023)
YouTube link:
Prof. Dr. E. Verhagen
21 June 2023 at 15:00 CEST
Title:
Optomechanical meta-matter: From nonreciprocity to non-Hermitian topology
Abstract:
Non-Hermitian bosonic systems with carefully tailored distributions of gain and loss have attracted intensive interest due to the unique spectral and dynamical properties associated with parity-time symmetry and exceptional point degeneracies, and their functions in signal generation, routing, and sensing. We investigate small synthetic networks of nanomechanical resonators that are created through time-modulated laser control fields. This parametric control allows generating arbitrary quadratic bosonic Hamiltonians for nanomechanical motion. We show that by combining particle-conserving interactions with optomechanically-induced squeezing, many interesting non-Hermitian phenomena result: Chiral amplification, dynamical stability controlled by geometric phases, and quadrature nonreciprocity: a type of phase-dependent unidirectional transmission that can occur without breaking time-reversal symmetry. We use these networks to experimentally demonstrate a bosonic analog of the Kitaev-Majorana chain - a non-Hermitian topological phase with potential applications in directional signal amplification and sensing.
YouTube link:
Prof. Dr. O. Zilberberg
24 May 2023 at 15:00 CEST
Title:
Strongly correlated open system dynamics: From quenched impurity physics to melted exceptional points
Abstract:
In recent years, there has been rapid development in control and manipulation of coherent quantum systems. In reality, however, such coherent effects are always impacted by coupling to an environment. In my talk, I will introduce several cases where the environment competes with the coherent system and induces novel population inversions, thus completely altering the closed system’s signatures. Specifically, I will start by showing how dissipation in driven nonlinear bosonic cavities leads to a dramatic change of the phase diagram, and then move on to generalize such effects to light-matter systems. Note that phase transitions in such systems are commonly appearing alongside exceptional points in the excitation spectra, and I will tell a short tale on how many-body interactions can quench the transition. I will then move to discuss the impact of non-Ohmic noise on coherent transport signatures in quantum wires, and how quantum measurement backaction can induce a population switching in an open double quantum dot device.
YouTube link:
Prof. Dr. A. Metelmann
17 May 2023 at 15:00 CEST
Title:
Dissipation and non-linearity as a formidable resource, or how a shark can be helpful
Abstract:
Engineered quantum systems are artificial mesoscopic systems whose dynamics are governed by the laws of quantum mechanics. Prominent examples of these mesoscopic systems are ultracold trapped atoms and ions, superconducting circuits and electro/optomechanical systems. These systems are powerful candidates for future quantum technologies and to study the basic laws of quantum mechanics. Every platform comes with its unique challenges, but all face the general issue of (unwanted) nonlinear processes and dissipation. However, in this talk we will discuss how dissipation and nonlinearity can be utilized to form a profitable resource for control, manipulation and read-out of engineered quantum systems. This includes the fascinating aspect of turning dissipation, which in general limits the performance of an experiment, into an advantageous tool. In this talk we will show how engineered dissipative processes allow for the steady-state entanglement of hot propagating modes. In addition, we present theoretical and experimental results for enhanced back-action cooling in nonlinear magnetomechanical systems.
YouTube link: