Quantum Mpemba Effect in CFT and Quantum Simulation†
Date: 7/24, 14:00~15:00
Room: D413 at Institutes of Natural Sciences
Speaker: Harunobu Fujimura (Osaka University)
Abstract:
The quantum Mpemba effect is a counterintuitive nonequilibrium phenomenon in which an initially more asymmetric state can restore symmetry faster than a less asymmetric one. In this talk, I will discuss this effect in conformal field theories from the viewpoint of entanglement asymmetry, a quantitative measure of symmetry breaking in a subsystem. After introducing the basic ideas of the quantum Mpemba effect and entanglement asymmetry, I will explain how CFT techniques allow us to analytically study the time evolution of symmetry restoration following local excitations. I will then present our results for CFTs with non-Abelian global symmetries. Finally, I will briefly discuss an ongoing complementary approach using quantum simulation, which aims to study the quantum Mpemba effect in more general non-CFT many-body systems.
Tensor Renormalization Group Approach to the Sign Problem†
Date: TBD
Room: D413 at Institutes of Natural Sciences
Speaker: Hayato Aizawa (University of Tsukuba)
Abstract:
In lattice quantum chromodynamics (QCD), the sign problem hinders the analysis of systems with finite density or a $\theta$ term using conventional Monte Carlo simulations. The tensor renormalization group (TRG) is a powerful approach that avoids this problem, although its application to higher dimensions or large internal degrees of freedom remains computationally challenging.
In this talk, we present recent progress on two toy models toward addressing the sign problem in QCD using TRG. The first model is the two-dimensional $CP(1)$ model with a $\theta$ term.
We present a computation of the step-scaling function (SSF) and an investigation of infrared conformality at $\theta=\pi$. The second model is the three-dimensional complex scalar model at finite density, which is computationally more challenging. We investigate the Silver Blaze phenomenon and the universality class of the associated critical point.
Abstract: The subject of my presentation is the lattice QCD for precision physics of muon anomalous magnetic moments (muon g-2). I will begin with a brief review of the current status based on the whitepaper. In the main part, I will show the latest Lattice QCD estimates of the muon g-2 in outstanding precision by quoting the Mainz-CLS and BMW results and compare them with the experimental measurements and the dispersive approach. The comparison indicates some tensions among theoretical estimates on the hadron vacuum polarization (HVP). I further focus on the QED and electroweak running couplings which also depend on the HVP, and discuss how the tension comes out. Finally, I will explain the prospect of the PACS10 - KEK/JPARC joint project, which aims at more precise calculation / measurements of the muon g-2.
Abstract: Tensor renormalization group (TRG) is a powerful numerical tool for calculating the partition function of statistical systems. Based on the idea of real-space renormalization group, the system is coarse-grained at each step. We consider a method for extracting derivatives of the partition function approximated by TRG by directly differentiating the renormalization map. We show that the accuracy of approximated thermodynamic quantities, such as internal energy and specific heat is drastically improved compared with the usual method, while keeping the numerical cost at the same order.
Utilizing Gauss’s law in Hamiltonian simulation of lattice gauge theory on quantum computers†
Date: 5/22, 14:00~15:00
Room: CCS Meeting Room B
Speaker: Lento Nagano (Keio University)
Abstract: In recent years, there has been growing interest in applying quantum computing to lattice gauge theory simulations, aiming to achieve advantages over classical methods. The Hamiltonian formalism is particularly natural in this context, but it requires imposing Gauss’s law constraints to maintain gauge invariance. A key issue is therefore to incorporate these constraints into qubit encodings and quantum algorithms in a scalable way.
In this talk, I will explain how Gauss’s law can be integrated with simulation methods and used not only to enforce gauge symmetry but also to mitigate or correct hardware errors and reduce computational resources. I will discuss these ideas through examples of (1+1)-dimensional and (2+1)-dimensional lattice gauge theory.
Effective field theory for dissipative photons from higher-form symmetries†
Date: 5/8, 14:00~15:00
Room: CCS Meeting Room B
Speaker: Genki Yoshimura (Osaka University)
Abstract: Symmetry provides a powerful guiding principle in theoretical physics. Effective field theories based on global symmetries and their patterns of spontaneous breaking have been remarkably successful in capturing universal long-wavelength dynamics. This framework can be further refined using generalized global symmetries, for instance higher-form symmetries. Electromagnetism in vacuum is a well-known example of spontaneous breaking of a U(1) 1 form symmetry, with the photon emerging as the associated Nambu–Goldstone mode. However, the behavior of photons in this broken phase at finite temperature, i.e. photons in the insulator, has not been studied from the perspective of the U(1) 1-form symmetry. Building on this symmetry structure, we construct an effective field theory that incorporates fluctuations and dissipation beyond purely Hermitian dynamics, formulated within the Schwinger–Keldysh formalism. Our theory provides a model-independent description of dissipative photon dynamics, identifying higher-form symmetry as the organizing principle of their effective time-evolution.
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