理化学研究所 生体非平衡物理学理研白眉研究チームの川口喬吾です。

シカゴ大学の花井亮さんに、アクティブマター・非相反な系の相転移についてのセミナーをお願いしました。本セミナーは、新学術領域「情報物理学でひもとく生命の秩序と設計原理」が主催するIPBセミナーシリーズの一環として、共同開催となります。

Date and time: Nov 4th (Wed) 10:00-11:00 (Japan time)

Place: Zoom
(このフォームにて要参加登録: セミナー開始１時間前にZoom linkを送信します)
(Register here, Zoom link will be sent 1 hour before the seminar)

Speaker: 花井亮さん Ryo Hanai (Department of Physics, University of Chicago)

Title: "Phase transitions in non-reciprocally interacting matter"

Abstract:
   Usually, microscopic objects such as atoms and molecules obey the Newton's third law, i.e., they interact in a reciprocal way. However, non-reciprocality is a common feature of active systems that arise in a broad context of science ranging from social sciences, biology to physics: A peregrine falcon chases a dove because of their non-reciprocal “interaction”; Neural networks are composed of inhibitory and excitatory neurons that couple non-reciprocally; Social networks are composed of nodes with non-reciprocal connectivity; Synthetic physical non-reciprocal interactions can be realized in complex plasma and optical nanoparticle systems.
   Despite its ubiquitous presence in Nature, the collective properties of such non-reciprocally interacting many-body systems are poorly understood. In this talk, I will generalize the Ginzburg-Landau theory of equilibrium phase transitions to be applicable to non-reciprocal matter [1]. I show that non-reciprocity gives rise to unusual many-body phases and transitions controlled by spectral singularities called exceptional points. The emergent collective phenomena range from active time (quasi)crystals to exceptional point enforced pattern formation and hysteresis. I illustrate these phenomena by giving three paradigmatic examples of self-organization generalized to have non-reciprocal interactions: synchronization, flocking, and pattern formation.
   If time allows, I will also talk about a quantum many-body system (exciton-polariton system) that exhibits analogous phase transitions [3] and critical phenomena ("critical exceptional point"), which is associated with a new universality class with anomalously giant phase fluctuations (that diverges at d≤4) and enhanced many-body correlations (that becomes relevant at d<8) [4].

[1] M. Fruchart*, R. Hanai*, P. B. Littlewood, and V. Vitelli, arXiv:2003.13176.
[2] T. Kato, Perturbation theory for linear operators, 2nd ed. (Springer, 1984).
[3] R. Hanai, A. Edelman, Y. Ohashi, and P. B. Littlewood, Phys. Rev. Lett. 122, 185301 (2019).
[4] R. Hanai and P. B. Littlewood, Phys. Rev. Research 2, 033018 (2020).

講演は英語で行われます。
The talk will be given in English.