13.10.26 – 16:00 in  D.10.08 

Conserved Currents and Chiral States in Quantum Spin Chains

Dr. Chenan Wei

Can a quantum spin chain support a current-carrying state that is both a ground state of a local Hamiltonian and an exact excited eigenstate of a familiar reference model? In this talk, I explain how a bias coupled to a conserved energy-current charge selects such states without changing the reference eigenvectors. Starting with spin-chain excitations and an exactly solvable free-fermion example, I show why a finite current threshold can occur in a gapless system and how Bethe-ansatz dressing determines the interacting instability. The construction exposes chiral, ordered, and critical eigenstates at finite reference-energy density and extends to 

spin-1 chains, where the current acquires additional operator dressing. I then discuss proposed experimental routes for zigzag geometries. A gyrotropic cavity can generate complex electronic hopping and chiral exchange, while programmable spin operations offer a complementary route to the required three-spin terms. The experimental requirements include the orientation of triangular loop phases, competing exchange couplings, and preparation that can change conserved sectors. Direct chirality measurements, spectroscopy, and prepare-and-release dynamics provide distinct tests of the mechanism.

15.10.2026 - 15:00 D.10.08

Statistical properties of quadrangular surfaces

Dr. Hrand Topchyan

We investigate the statistical properties of random quadrangular surfaces generated by different randomization procedures: the Gruzberg-Klümper-Nuding-Sedrakyan (GKNS) construction, and two newly introduced generalizations of dynamical triangulations (DT), dynamical (DQ) and general quadrangulations (GQ). We formulate these surfaces within a unified graph-theoretic framework and establish the relationships between the elementary operations defining the different ensembles. For GKNS surfaces, we demonstrate that the construction is equivalent to two mutually constrained percolation processes and determine the associated critical point and critical exponents, revealing deviations from ordinary percolation. For DQ and GQ, we analyze the underlying Markov chains and determine the scaling of mixing and relaxation times. We further analyze all three ensembles through their degree distributions, degree correlations, distance statistics, and Hausdorff dimensions. While DQ exhibits exponentially decaying degree distributions and geometric properties similar to DT, GKNS and GQ display broad, scale-free degree distributions. Moreover, GKNS surfaces possess an asymptotic Hausdorff dimension ΔH≈2, whereas DQ and GQ approach ΔH≈4, similarly to DT. This indicates that DQ is compatible with the universal behavior of DT, while GKNS and GQ define distinct classes of random geometry, implying a different underlying measure in the space of random surfaces and a possible geometric framework for a new class of noncritical string theories.