2025年6月3日（火）13:30~（第4回）(4th: 13:30-, June 3, 2025)
理学部4号館1220教室 (Room No. 1220, Science 4th Bldg.)
Speaker: Takagi Ryuji (University of Tokyo)
Title: Universal work extraction in quantum thermodynamics
Abstract:
Evaluating the maximum amount of work extractable from a nanoscale quantum system is one of the central problems in quantum thermodynamics. Previous works identified the free energy of the input state as the optimal rate of extractable work under the crucial assumption: experimenters know the description of the given quantum state, which restricts the applicability to significantly limited settings. Here, we show that this optimal extractable work can be achieved without knowing the input states at all, removing the aforementioned fundamental operational restrictions. We achieve this by presenting a universal work extraction protocol, whose description does not depend on input states but nevertheless extracts work quantified by the free energy of the unknown input state. Our results clarify that, in spite of the crucial difference between the state-aware and state-agnostic scenarios in accomplishing information-theoretic tasks, whether we are in possession of information on the given state does not influence the optimal performance of the asymptotic work extraction.
2025年6月10日（火）13:30~（第5回）(5th: 13:30-, June 10, 2025)
理学部4号館1220教室 (Room No. 1220, Science 4th Bldg.)
Speaker: Alberto Nardin (Université Paris-Saclay - LPTMS)
Title: Spin fractionalization in fractional quantum Hall systems
Abstract:
The spin-statistics theorem is a pillar of our description of the world, classifying quantum particles into bosons or fermions according to their spin, integer or fractional. In 2D systems, particles with intermediate “fractional” statistics, called anyons, are possible, and they satisfy a generalized spin-statistics relation. A prototypical system in which exotic anyonic excitations have been shown to emerge are fractional quantum Hall states of matter, but not much attention has been devoted to their spin, especially on non-curved surfaces.
During this talk, I will discuss how the quasiparticles in fractional quantum Hall fluids, known for their anyonic behaviour, carry a well-defined and measurable spin which satisfies a spin-statistics relation [1]. Moreover, in analogy to their charge, I will detail how this spin is fractionalized between the quasiparticle deep in the bulk and the system’s edge [2]. Several examples, such as Laughlin, Moore-Read, and Read-Rezayi states, will be discussed.
[1] A. Nardin, E. Ardonne, L. Mazza, “Spin-statistics relation for abelian quantum Hall states”, Phys. Rev. B, 108 L041105 (2023)
[2] A. Fagerlund, A. Nardin, L. Mazza, E. Ardonne, “Spin fractionalization at the edge of quantum Hall fluids induced by bulk quasiparticles”, arXiv:2412.14879