Staff

Roger Melko: Language models for quantum simulation

Abstract: As the frontiers of artificial intelligence advance more rapidly than ever before, generative language models like ChatGPT are poised to unleash vast economic and social transformation. In addition to their remarkable performance on typical language tasks (such as writing undergraduate research papers), language models are being rapidly adopted as powerful ansatze states for quantum many-body systems.  In this talk, I will discuss the use of language models for learning quantum states realized in experimental Rydberg atom arrays. By combining variational optimization with data-driven learning using qubit projective measurements, I will show how language models are poised to become one of the most powerful computational tools in our arsenal for the design and characterization of quantum simulators and computers.

Yong-Baek Kim: Quantum Spin Liquids and Criticality in Multipolar Materials

Abstract: Multipolar quantum materials possess local moments carrying higher-rank quadrupolar or octupolar moments. These higher-rank multipolar moments arise due to strong spin-orbit coupling and local symmetry of the crystal-electric-field environment. In magnetic insulators, the interaction between multipolar local moments on frustrated lattices may promote novel quantum spin liquids. In heavy fermion systems, the interaction between multipolar local moments and conduction electrons may lead to unusual non-Fermi liquids and quantum criticality. In this talk, we first discuss a novel quantum spin ice state, a three-dimensional quantum spin liquid with emergent gauge field, that may have been realized in Ce₂Zr₂O₇ and Ce₂Sn₂O₇, where Ce³⁺ ions carry dipolar-octupolar moments. We present a theoretical analysis of possible quantum spin ice states in this system and compare the theoretical results of dynamical spin structure factors with recent neutron scattering experiments. Next, we present a theoretical model to describe the unusual Kondo effect and quantum criticality in Ce₃Pd₂₀Si₆, where Ce³⁺ moments carry a plethora of dipolar, quadrupolar, and octupolar moments. We show that two consecutive Kondo-destruction-type phase transitions can occur with the corresponding Fermi surface reconstructions. We compare these results with existing experiments and suggest future ultrasound experiments for the detection of emergent quantum critical behaviors.

Young-June Kim: Alpha-RuCl3: a progress report

Abstract: A bond-dependent anisotropic magnetic interaction called the Kitaev interaction can be found in honeycomb lattice materials with strong spin-orbit coupling, which has made a profound impact on quantum magnetism research. In particular, alpha-RuCl3 has been heralded as a realization of the Kitaev quantum spin liquid state, an elusive new state of matter that harbours Majorana fermions. In this talk, I will give a brief overview of the current status of research on alpha-RuCl3 and discuss recent experimental developments and a few surprising findings using ultra-high-quality samples grown in our laboratory. Our samples have minimal stacking faults even at low temperatures, allowing us to determine the low-temperature crystal structure unambiguously. We also found that the magnetic properties are surprisingly sensitive to the inter-layer configuration, giving rise to various magnetic transition temperatures. We also compare low-energy spin-orbit excitations in various Kitaev materials using resonant inelastic x-ray scattering (RIXS). We found that non-local physics is important for describing the spin-orbit excitations in these materials, in contrast to the conventional belief that local Jeff=1/2 physics is sufficient in these compounds.