September 2024

Abstracts of the Quantum Center Lunch Seminar

Date: Thursday, September 5, 2024
Place: ETH Zurich, Hönggerberg, HPF G 6
Time: 12:00 - 13:30

Quantum Scars in Lattice Gauge Theories

Thea Budde - High Performance Computational Physics (Marinkovic group), ETH Zurich

Gauge theories lie at the heart of the standard model and describe the physics of elementary particles. Classical simulations of these systems are often expensive, and many quantities are inaccessible entirely. Here, quantum simulators offer an exciting opportunity. Writing gauge theories as quantum many-body Hamiltonians opens the door to studying their dynamics throughout time. Quenches in simple gauge theories reveal rich physics, such as quantum many-body scars: the system fails to thermalize after a long time starting from a small subset of initial states. In my talk, I will introduce gauge theories in the Hamiltonian formalism and present recent results on quantum scars. These results can guide near-term experimental characterization of novel phenomena in gauge theories.

Exploring the 3D energy spectrum of Andreev bound states in a four-terminal Josephson junction

Tommaso Antonelli - Advanced Semiconductor Quantum Materials (Wegscheider group), ETH Zurich

Josephson junctions (JJs) are central components in superconducting circuits, used for both quantum applications and fundamental research. In my talk, I will discuss the physics of planar Josephson junctions formed in high-quality superconductor-semiconductor systems, where the supercurrent is carried by electronic modes called Andreev bound states (ABSs). In particular, multiterminal Josephson junctions are expected to harbor a novel class of ABSs, characterized by a topological band structure in the phase space [1-6]. I will present the experimental realization of a four-terminal JJ in a hybrid Al/InAs heterostructure, where three phase differences between the superconducting terminals are independently controlled. Using tunneling spectroscopy, we explore the ABS band structure across the entire 3D phase space. We identify spectral signatures indicative of hybridization among three ABSs, forming molecule-like states delocalized across all four terminals. These spectral features are well reproduced by theoretical simulations, which also predict the presence of Weyl nodes at specific phase coordinates, although such signatures remain experimentally elusive so far. Our work guides the realizations of topological states of matter in multiterminal superconducting devices, offering exciting opportunities for the investigation quantum phenomena and for applications.

[1] van Heck, B. et al., Phys. Rev. B 90, 155450 (2014).
[2] Yokoyama, T. et al., Phys. Rev. B 92, 155437 (2015).
[3] Riwar, R.-P. et al., Nat. Commun. 7, 11167 (2016).
[4] Eriksson, E. et al., Phys. Rev. B 95, 075417 (2017).
[5] Meyer, J. S. et al. Phys. Rev. Lett. 119, 136807 (2017).
[6] Klees, R. L. et al. Phys. Rev. Lett. 124, 197002 (2020).