Academic Year 2023

• New Fluctuation Theorems and Maxwell Demon
  • Jin Wang (Stony Brook University)
    
  • Date:2023/09/14 16:00 --
    
  • Place: Conference Room K206, Main Building, Yukawa Institute, Kyoto U. & 【Zoom】＊It will be held in hybrid.
    
  • Abstract:
    With increasing interest in the control of systems at the nano- and mesoscopic scales, studies have been focused on the limit of the energy dissipation in an open system by refining the concept of the Maxwell’s demon. To uncover the underlying physical principle behind a system controlled by a demon, we prove a previously unexplored set of fluctuation theorems. These fluctuation theorems imply that there exists an intrinsic nonequilibrium state of the system, led by the nonnegative demon-induced dissipative information. A consequence of this analysis is that the bounds of both work and heat are tighter than the limits predicted by the Sagawa-Ueda theorem. We also suggest a possible experimental test of these work and heat bounds.
• Quantum Mpemba effect
  • Amit Kumar Chatterjee (YITP, Kyoto University)
    
  • Date: 2023/09/06 16:00 --
    
  • Place: Seminar Room K202, Main Building, Yukawa Institute, Kyoto U. & 【Zoom】＊It will be held in hybrid.
    
  • Abstract:
    Mpemba effect refers to the counter-intuitive phenomenon where a hotter object can cool down faster than a colder copy of the same object. In spite of some theoretical as well as experimental advances of it in the classical domain, the quantum counterpart of the Mpemba effect, specifically in temperature, has remained unexplored. In this talk, we demonstrate the quantum Mpemba effect by showing that temperatures of two copies of a quantum system, one initially hotter than the other, can cross each other after some time and thereafter reverse their identities, i.e. hotter becomes colder and vice versa, before reaching the same final temperature. In fact, we show such crossing of trajectories characterizing the quantum Mpemba effect, can occur in several other observables including energy, entropy etc. Our theoretical results on quantum Mpemba effect are primarily based on a quantum dot connected to two reservoirs. In the later part of the talk, we discuss how exceptional points and complex eigenvalue spectrum can lead to multiple quantum Mpemba effect (where crossing occurs multiple times) in a two- level driven dissipative system.
  • Reference:
    A. K. Chatterjee, S. Takada, and H. Hayakawa, Phys. Rev. Lett. 131, 080402 (2023).
• Nonequilibrium dynamics of charge and spin order in photo-pumped correlated systems
  • Sankha Subhra Bakshi (Harish-Chandra Research Institute)
    
  • Date: 2023/07/13 16:00 --
    
  • Place: Seminar Room K202, Main Building, Yukawa Institute, Kyoto U. & 【Zoom】*It will be held in hybrid.
    
  • Abstract:
    When a correlated system with long range charge or spin order is perturbed by a laser pulse and then allowed to evolve in isolation the dynamics that is observed depends primarily on the energy absorbed. At small absorbed energy one expects to see the excitation of normal modes, then the effect of mode coupling, and, ultimately, at large energy input, the complete loss of order. The dynamics, and the long time state, between these extreme cases is however hard to guess, and reveals some surprises. This talk will look at the result of laser pumping in two cases: (i) charge order obtained in the Holstein model, and (ii) the triangular lattice Mott insulator in the half-filled Hubbard model. We use an equation of motion scheme that at equilibrium would have led to mean field theory, but out of equilibrium captures the nonlinear spatio-temporal dynamics of these systems. Beyond the extreme cases of normal mode response and loss of order, the Holstein problem reveals a "suppression-revival" dynamics of the order parameter at intermediate pumping, with a divergent revival timescale as the loss of order is approached. The Mott problem on the other hand shows the appearance of reduced moment ordered states which have no equivalent at equilibrium. We construct some energy landscapes, involving a nonequilibrium electron population, to explain these intriguing features.
• Time crystals in open atom-cavity systems
  • Jayson G. Cosme (University of the Philippines, Diliman )
    
  • Date: 2023/07/19 16:00 --
    
  • Place: Conference Room Y206, Yukawa Hall, Yukawa Institute, Kyoto U. & 【Zoom】 *It will be held in hybrid.
    
  • Abstract:
    Time crystals are phases of matter characterised by their robust emergent behaviour in time. They can be classified as either discrete or continuous depending on whether they spontaneously break discrete or continuous time translation symmetry, respectively. In this talk, I will present our findings on the first-ever observations of both types of time crystals - discrete and continuous - in a dissipative system. Specifically, we have demonstrated the emergence and investigated the key properties of time crystals in a cavity QED platform consisting of ultracold atoms coupled to the light field of a high-finesse optical cavity. For a periodically driven light-matter interaction strength, we show that the atom-cavity system emulates the paradigmatic discrete time crystal in the celebrated Dicke model. Interestingly, even in the absence of such a Floquet drive, we have predicted and experimentally observed time-periodic oscillations of the light field for sufficiently strong interactions. Owing to its robustness and spontaneous symmetry breaking of time, we have classified this dynamical phase as a continuous time crystal. Our series of works highlight how the interplay between driving, dissipation, and interaction could lead to non-equilibrium phases of matter.
• Nematic Torques in Scalar Active Matter
  • Gianmarco Spera (Université Paris Cité, Laboratoire Matière et Systèmes Complexes)
    
  • Date :2023/07/26 14:30--
    
  • Place: Seminar Room K202, Main Building, Yukawa Institute, Kyoto U. & [Zoom] *It will be held in hybrid
    
  • Abstract
    Active matter describes systems comprising elementary units able to exert non-conservative forces　on their environment. Activity leads to a fascinating variety of collective behaviours unmatched in passive　 systems, such as the transition to collective motion. The latter is arguably the most studied phase transition in active matter and the ordered phases emerging from the interplay between self-propulsion and aligning interactions have naturally attracted a lot of attention [1]. In this talk, I will instead focus on the role of aligning interactions in the disordered phase. In particular, I will show that nematic alignment plays an unexpected role in the ‘high-temperature’ phase: it can induce or suppress phase separation, increase particle accumulation at boundaries, and suppress demixing in systems comprising active and passive particles. I will then show how all these phenomena can be understood by introducing a field-theoretical framework to go beyond the mean-field description of the system. In the presence of nematic torques, fluctuations are then shown to enhance polar order, leading to an increase in the particle persistence length. In turn, the latter accounts quantitatively for all the phenomena reported above. To show this, I will briefly describe a new theory for motility-induced phase separation in the presence of aligning torques. [2]
  • References
    [1] H. Chat´e, “Dry aligning dilute active matter.” Ann. Rev. of Cond. Matt. Phys. 11 (2020): 189-212.
    [2] G. Spera, C. Duclut, M. Durand, and J. Tailleur, preprint arXiv:2301.02568 (2023), submitted to Physical Review Letters
    
• Non-reciprocity across scales in active mixtures
  • Alberto Dinelli (Université Paris Cité, Laboratoire Matière et Systèmes Complexes)
    
  • DateL 2023/07/26 16:00 --
    
  • Place: Seminar Room K202, Main Building, Yukawa Institute, Kyoto U. & [Zoom] *It will be helt in hybrid
    
  • Abstract
    In active matter, the lack of momentum conservation makes non-reciprocal interactions the rule rather than the exception. Non-reciprocity is responsible for a wealth of emerging behaviors that are hard to predict starting from the microscopic scale, due to the absence of a generic theoretical framework out of equilibrium. In this talk, we consider bacterial mixtures that interact via mediated, non-reciprocal interactions like quorum-sensing and chemotaxis. By explicity relating microscopic and macroscopic dynamics, we show that non-reciprocity may fade as coarse-graining proceeds, leading to large-scale bona fide equilibrium descriptions. In turns, this allows us to account quantitatively, and without fitting parameters, for the rich behaviors observed in microscopic simulations including phase separation, demixing or multi-phase coexistence. We also derive the condition under which non-reciprocity is strong enough to survive coarse-graining, leading to a wealth of dynamical patterns. Again, the explicit coarse-graining of the dynamics allows us to predict the phase diagram of the system starting from its microscopic description. All in all, we show that the fate of non-reciprocity across scales is a subtle and important question.
  • References
    [1] A. Dinelli, J. O’Byrne, A. Curatolo, Y. Zhao, P. Sollich, J. Tailleur, submitted to Nat. Comm. (2022).
    
• Effects of particle mass and shape on gas diffusion
  • Fumiaki Nakai (Nagoya University)
  • Date: 2023/06/21 16:00 --
    
  • Place:Seminar Room K202, Main Building, Yukawa Institute, Kyoto U. & 【Zoom】 *It will be held in hybrid.
    
  • Abstract:
    A small particle immersed in a fluid shows random motion due to the collisions of the surrounding particles. The random motion can be widely described using the Langevin equation, and the stochastic process of displacement obeys the Gaussian process. It has been known that such a simple description does not work for complex fluids: colloidal systems, glass-forming liquids, or polymeric liquids. However, even in simple gas systems, we found that unusual non-Gaussian diffusion emerges when the mass ratio is sufficiently large or the particle shape is highly asymmetric. In the presentation, I explain the effects of mass and shape on particle diffusion.
  • References
    F. Nakai, M. Kröger, T. Ishida, T. Uneyama, Y. Doi, and Y. Msubuchi, Phys. Rev. E 107, 044604 (2023).
    F. Nakai, Y. Masubuchi, Y. Doi, T. Ishida, and T. Uneyama, Phys. Rev. E 107, 014605 (2023).