QMSI Seminar: Dr. Yu Zhang, Los Alamos National Laboratory

Scalable Ab Initio Quantum Many-Body Methods for Fermion-Boson Interactions

Accurate treatment of fermion–boson interactions is essential to understanding cavity and phonon-polaritonic phenomena. I will present scalable ab initio methods that move beyond mean-field theory to capture strong correlations in coupled electron–photon and electron–phonon systems. Building on quantum electrodynamics Hartree–Fock (QEDHF), we develop a variational displacement and squeeze transformation that captures anharmonic photon-field fluctuations and unifies weak to strong coupling regimes. To tackle strong electron-electron and photon-mediated electron-electron correlations, we introduced a quantum electrodynamics auxiliary-field quantum Monte Carlo (QED-AFQMC) framework that delivers numerically exact ground states with controlled bias and explicit light–matter entanglement. I will also present a quantum theory for hyperbolic phonon polaritons in twisted α-MoO₃ bi-slabs, providing first-principles predictions of twist-tunable dispersions and phonon–photon hybridization in anisotropic media. Together, these advances establish a scalable platform for predictive control of polaritonic phenomena in molecules and van der Waals materials.

Speakers

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  Dr. Yu Zhang

  Staff Scientist
  Los Alamos National Laboratory

  Yu Zhang received his BSc in Physics from Sun Yat-Sen University in 2010 and his Ph.D. in Chemical Physics from The University of Hong Kong in 2015. From 2015 to 2017, he worked as a Postdoctoral Fellow at Northwestern University. Yu joined Los Alamos National Laboratory (LANL) in 2018 as a Director's Postdoctoral Fellow and transitioned to a staff scientist in 2019. He is the recipient of the Laboratory Directed Research and Development Early Career Research Award (2022) and the DOE Office of Science Early Career Research Award (2023). Yu's research lies at the intersection of chemical physics and quantum physics, with a focus on developing and applying modern electronic structure theories and quantum dynamics methods to explore the electronic, optical, and dynamical properties of nanomaterials for applications in energy and quantum technologies. Yu’s current interests include quantum computation, quantum information science, light-matter interactions, open quantum systems, and non-adiabatic quantum dynamics.