Students Colloquium 
TYPE  Colloquium 
Speaker:  Matan EvenTzur / Amit Goft / Omer Granek / Aldana Grichener 
Affiliation:  Technion 
Organizer:  Yotam Soreq 
Date:  08.07.2024 
Time:  14:30  16:00 
Location:  Lidow Rosen Auditorium (323) 
Abstract:  Matan EvenTzur: High harmonic generation driven by squeezed light High harmonic generation (HHG) is a nonlinear process where intense light induces matter to emit coherent ultraviolet and Xray radiation. Traditionally driven by classical laser light, recent advancements in generating intense ultrashort pulses of squeezed light are making HHG with nonclassical light feasible. This talk explores recent theoretical & experimental advances showing that squeezed light significantly alters the HHG spectrum and photon statistics, potentially leading to higher harmonics, shorter attosecond pulses, and squeezed high harmonics. Amit Goft: Building Topological Materials from Thermodynamic Topological Defects Topological defects in thermodynamic phases are characterized by winding numbers of order parameters. Similarly, topological phases in the tenfold classification of insulators and superconductors are characterized by Chern and winding numbers. We show that both situations can be described by a single formalism, using the notion of the symbol of a Hamiltonian which contains all relevant topological information. The symbol generalizes Bloch Hamiltonians and order parameters. Vacancies in graphene offer a useful example. Omer Granek: Metastability of Flocks We study the stability of the ordered phase of flocking models that break either a discrete or a continuous symmetry. For flocks that break a discrete symmetry, using both the active Ising model and a hydrodynamic description, we show that droplets of particles moving in the direction opposite to that of the ordered phase nucleate and spread ballistically in all directions. The result implies that, in the thermodynamic limit, discretesymmetry flocksand, by extension, continuoussymmetry flocks with rotational anisotropyare globally unstable in all dimensions. In contrast, using the active XY model and a hydrodynamic description, we find flocks that break an isotropic continuous symmetry to be globally stable, albeit within a qualitatively narrower region of the phase diagram compared to previous studies. The results imply that, in contrast to equilibrium systems, breaking a continuous symmetry is easier than a discrete one. Aldana Grichener: Formation of the heaviest elements in the Universe in neutron star – core mergers The origin of the heaviest elements in the Universe remains an open question in nuclear astrophysics. In this colloquium, I will focus on a scenario in which the heaviest elements are produced during the merger of a neutron star (NS) with the core of a giant star. When a massive star and a NS coexist in a close binary system, the immense swelling of the star as it evolves into a red supergiant might result in the engulfment of the NS, which then keeps orbiting inside its giant companion. Using various numerical methods, we found that the extreme conditions around the NS in this scenario lead protons and electrons to merge into neutrons, which are then captured by iron nuclei, producing heavy elements at a rate that could account for their formation in our Galaxy.
