MajuLab Seminar by Wen Wei Ho – 20 June 2024

Wen Wei Ho is an Assistant Professor of Physics at the National University of Singapore and also a Fellow at the Centre for Quantum Technologies, specializing in the theory of quantum many-body dynamics studied through the lens of quantum information. He is a recipient of the National Research Foundation (NRF) Fellowship of Singapore in 2023, and is also a Presidential Young Professor at NUS. Wen Wei obtained his PhD from the University of Geneva in 2017 under the guidance of Prof. Dmitry Abanin, and prior to joining NUS, completed two postdoctoral stints at Harvard University and Stanford University. Some of his works in the past have included developing a rigorous theory of prethermalization in driven quantum many-body systems, quantum many-body scars and time crystals. He also collaborates extensively with experimentalists working on cold atoms and arrays of trapped Rydberg atoms in pushing the boundaries of quantum information science.

Novel forms of quantum ergodicity and equilibration from the lens of quantum information

Thermalization in a closed quantum system is defined by the dynamical approach of local observables toward universal expectation values, computed within a thermal Gibbs state. In this talk, I want to explain how a more refined notion of quantum equilibration can be studied by resolving the local state of a system via conditioning it on measurements of the complement (the “bath”). This yields an ensemble of pure conditional states — representing a physically motivated unraveling of the reduced density matrix — that describes a wavefunction distribution over the Hilbert space. I will show that for generic complex quantum systems, the ensemble attains a common form: it tends towards the “maximally entropic” distribution subject to constraints from conservation laws, which has the special quantum information-theoretic property of possessing minimal accessible information. This constitutes a form of equilibration beyond standard quantum thermalization, which has been dubbed “deep thermalization”. I will demonstrate the universality of this phenomenon across the physically distinct systems of discrete-variable spin systems and continuous-variable bosonic Gaussian systems, where deep thermalization takes different forms but is still governed by the same principle. Our results demonstrate the power of quantum information theoretic frameworks in unveiling new physical phenomena and principles in quantum dynamics and statistical mechanics

MajuLab is an international joint research unit of the CNRS, UCA, SU, NUS and NTU in Singapore (IRL 3654), hosted by CQT and SPMS.