Find the upcoming seminars below.

TQM seminar #29 : March 14 2024, 2pm (LPTMC seminar room, towers 13-12, 5th floor, room 523)

Andrej Mesaros (LPS Orsay)

Topological Defects in Spin-Orbit Coupling

Observing defects in a system has been a useful tool for identifying the locally ordered state. Recently, topological defects have become an essential tool for topological systems, which range from electrons to macroscopic metamaterials, because they can probe or even create the non-local order. I will briefly overview the ideas of topological defects and states, and then introduce electronic topological insulators and superconductors, with the important role of Spin-Orbit Coupling (SOC).

I will discuss our two recent theoretical results. First, experiments on graphene haven’t been able to enhance the type of SOC which creates a bulk topological insulator state and its desired robust edge states. Our prediction is that domain-wall defects in the experimentally-induced type of SOC (“valley-Zeeman” type), already carry the desired robust one-dimensional states.

I will also discuss microscopy experiments on superconducting monolayer of lead(Pb) grown over islands of cobalt atoms, which shows island edge modes, but also unexpected point-like electronic excitations on island centers. We theoretically find that a vortex defect in Rashba-type SOC fully explains puzzling real-space and spectral features of this experiment. The vortex excitation is interpreted as the highly-sought point-like Majorana bound state.

TQM seminar #30 : May 2 2024, 2pm (LPTMC seminar room, towers 13-12, 5th floor, room 523)

Dganit Meidan (BGU, Beer-Sheva, IsraĆ«l)

Theory of free fermion dynamics – from monitored to post selected evolution

Monitored quantum systems undergo Measurement-induced Phase Transitions (MiPTs) stemming from the interplay between measurements and unitary dynamics. When the detector readout is post- selected to match a given value, the dynamics is generated by a Non-Hermitian Hamiltonian with MiPTs characterized by different universal features. Here, we derive a partial post-selected stochastic Schrodinger equation based on a microscopic description of continuous weak measurement. This formalism connects the monitored and post-selected dynamics to a broader family of stochastic evolution. We apply the formalism to a chain of free fermions subject to partial post-selected monitoring of local fermion parities. Within a 2-replica approach, we obtained an effective bosonized Hamiltonian in the strong post-selected limit. Using a renormalization group analysis, we find that the universality of the non-Hermitian MiPT is stable against a finite (weak) amount of stochasticity. We further show that the passage to the monitored universality occurs abruptly at finite partial post-selection, which we confirm from the numerical finite size scaling of the MiPT. Our approach establishes a way to study MiPTs for arbitrary subsets of quantum trajectories and provides a potential route to tackle the experimental post-selected problem.

TQM seminar #31 : May 23 2024, 2pm (LPTMC seminar room, towers 13-12, 5th floor, room 523)

Nicolas Bergeal (LPEM, ESPCI Paris)