Academic Year 2021

• Geometrical Quantum Chemical Engine and Maxwell’s demon 【Onsite & Zoom】
  • Ryosuke Yoshii (Sanyo-Onoda City University)
  • Date: 2022/03/23 16:00 --
  • Place: Conference Room K202, Main Building, Yukawa Institute, Kyoto U. & Online (ZOOM*)
    *People interested in attending the seminar should register with google form.
  • Abstract:
    We theoretically study an entropy production and a work extracted from a system connected to two reservoirs by periodic modulations of chemical potentials of the reservoirs and one parameter in the system Hamiltonian under an isothermal condition [1,2]. We find that the modulation of parameters can drive the geometrical state, which is away from nonequilibrium steady state. As a result, the driven system cannot reach the nonequilibrium steady state at which the relative entropy takes the minimum value. With the aid of this property, we construct Maxwell’s demon in which the relative entropy increases with time, and we can extract the work, if we begin with the nonequilibrium steady state without modulations of parameters. We employ the Anderson model to demonstrate that the relative entropy can increase with time.
  • Reference
    [1] H. Hayakawa, V.M.M. Paasonen, and R.Yoshii, arXiv:2112.12370, 2021.
    [2] R. Yoshii and H. Hayakawa, in preparation.
• Statistical property of the stochastic system with odd elasticity 【Onsite & Zoom】
  • Kento Yasuda (RIMS, Kyoto University)
  • Date: 2021/12/08 16:00 --
  • Place: Conference Room K102, Main Building, Yukawa Institute, Kyoto U. & Online (ZOOM*)
    *People interested in attending the seminar should register with google form.
  • Abstract:
    Recently, the concept of odd viscosity and elasticity has been introduced to describe interactions in the active materials [1]. To describe the stochastic dynamics of a micromachine such as an enzyme, we have considered the over damped Langevin equations with odd elasticity which represents the activity induced by catalytic chemical reaction. In this talk, we focus on three statistical quantities, the time-correlation functions, the most probable path, and the average swimming velocity. As the first topic, we focus on the time reversal symmetry of time-correlation functions and show that it will be broken in the presence of odd elasticity [2]. The time reversal symmetry holds for the cross-correlation function for systems in equilibrium, such symmetry does not exist for non-equilibrium systems. We found that the time reversal symmetry of time correlation functions is broken in proportion to the odd elasticity. In the second work, we investigate how the presence of odd elasticity influences the most probable path that is derived by the variation of the OM integral, i.e., the OM variational principle. We show that the most probable outward path is different from that of the return path in micromachines, and hence the whole process becomes non-reciprocal due to odd elasticity [3]. In the last topic, we propose a novel type of thermally driven microswimmer in which the three spheres are connected with springs having not only even elasticity, but also odd elasticity [4]. We explicitly demonstrate that the proposed stochastic “odd microswimmer” can exhibit directional locomotion as a result of odd elasticity.
  • Reference
    [1] C. Scheibner et al., Nat. Phys. 16, 475 (2020).
    [2] K. Yasuda et al., in preparation.
    [3] K. Yasuda et al., arXiv:2110.05822, to be published in JPSJ.
    [4] K. Yasuda et al., J. Phys. Soc. Jpn. 90, 075001 (2021).
• Stochastic finite range processes: non-equilibrium steady state and observables【Onsite & Zoom】
  • Amit Kumar Chatterjee (YITP, Kyoto University)
  • Date: 2021/12/03 11:00 --
  • Place: Conference Room K206, Main Building, Yukawa Institute, Kyoto U. & Online (ZOOM*)
    *People interested in attending the seminar should register with google form.
  • Abstract:
    We consider a generic class of non-equilibrium stochastic processes on one dimensional periodic lattices, where particle from a randomly chosen lattice site can hop to its nearest neighbors. The hop-rates however, in general, can depend on the departure and arrival lattice sites as well as a finite number of neighboring lattice sites. These stochastic processes, generalizing the interaction range from nearest or next nearest neighbors to a general finite number of neighbors, is thereby named as finite range processes [1]. Inspired by the detailed balance condition leading to equilibrium Gibbs-Boltzmann distribution, we will show how generalized techniques like pairwise balance condition [1], h-balance condition [2] etc. can exactly solve the non-trivial non-equilibrium steady state probability distributions of finite range processes. Consequently, one can analytically calculate observables e.g. spatial correlations, particle current etc. for these non-equilibrium steady states. Interestingly, for specific choice of the hop-rates, we will discuss how the stochastic finite range processes exhibit phenomena like negative differential mobility (decreasing current with increasing bias) [2], zero-current non-equilibrium states [2] and condensation (accumulation of macroscopic number of particles at a single lattice site) [1].
  • Reference
    [1] Physical Review E 92, 032103 (2015).
    [2] Physical Review E 98, 062134 (2018).
• What can we learn about amorphous solids from effective theories & black holes ?【Zoom】
  • Matteo Baggioli (Wilczek Quantum Center, School of Physics and Astronomy, Shanghai Jiao Tong University)
  • Date: 2021/11/05 14:30 --
  • Place: ZOOM*
    *People interested in attending the seminar should register with google form.
  • Abstract:
    In recent years, an intriguing correspondence between soft-matter and high-energy physics is emerging, including a possible link between elasticity of amorphous solids and rheology of black holes, but direct comparisons between theoretical predictions and experimental/simulation observations remain limited. Here, we investigate the effects of non-linear elasticity on yielding and entropy in amorphous materials, by considering first an effective field theory (EFT) and then a gravitational model in the spirit of the holographic principle. In this talk, I will give a brief introduction of the two techniques and how they can be applied to study the problem of non-linear elasticity. Finally, I will consider as a concrete example hyperelastic systems with power-law stress-strain curves and derive several interesting correlations which will then be checked against simulations in the follow-up talk by Yuliang Jin.
• Non-linear elasticity, yielding and theory in simulated amorphous solids【Zoom】
  • Yuliang Jin (Inst. of theoretical physics, Chinese Academy of Sciences / U. of Chinese Academy of Sciences)
  • Date: 2021/11/05 16:00 --
  • Place: ZOOM*
    *People interested in attending the seminar should register with google form.
  • Abstract:
    Densely jammed packings are prepared, with the help of a swap algorithm, to model athermal, deeply annealed amorphous solids satisfying the isostatic condition. These systems jam at large jamming densities well above the conventional J-point density, and display shear jamming and shear dilatancy behavior, as shown in previous studies [1,2]. Here [3] we explore their non-linear, shear hardening elastic properties, and find that a stronger shear hardening effect, which is originated from a deeper annealing, is correlated to a smaller yielding strain and a larger yielding stress. Accompanied with shear hardening, the system’s configurational entropy increases with the shear strain, implying a shear-induced rejuvenation effect. All these novel findings cannot be explained by popular rheology theories, including the state-following replica theory and the elasto-plastic model, while they agree qualitatively well with the predictions from effective field and gravitational theories, based on a holographic principle [4]. Finally, we show that, while the shear-hardening effect is absent in thermal hard spheres and athermal over-jammed soft spheres, it exists universally in deeply (either thermally or mechanically) annealed systems near the jamming transition, independent of dimensionality and friction. The results suggest that deep annealing and isostaticity are two essential factors for shear hardening.
  • Reference
    [1] Y. Jin and H. Yoshino, A jamming plane of sphere packings, Proc. Natl. Acad. Sci. U.S.A. 118, e2021794118 (2021).
    [2] V. Babu, D. Pan, Y. Jin, B. Chakraborty, and S. Sastry, Dilatancy, shear jamming, and a generalized jamming phase diagram of frictionless sphere packings, Soft Matter 17, 3121-3127 (2021).
    [3] D Pan, T Ji, M Baggioli, L Li, Y Jin, Non-linear elasticity, yielding and entropy in amorphous solids, arXiv:2108.13124 (2021).
    [4] Talk by Matteo Baggioli.
• Pumping current in a non-Markovian N-state model【Zoom】
  • Ville Matias Mikael Paasonen (YITP, Kyoto University)
  • Date: 2021/07/05 16:00 --
  • Place: ZOOM*
    *People interested in attending the seminar should register with google form.
  • Abstract:
    In the study of nonequilibrium dynamics of many-body systems, the Markov approximation is often used, where memory effects are ignored to obtain a time-local master equation. However, accurate modelling of many realistic systems leads to non-Markovian master equations, which include memory effects [1].
    It is also well-known that cyclic modulation of the control parameters of a system, such as reaction rate coefficients, bath temperatures or chemical potentials, can produce to net flow of a physical current, known as Thouless pumping, even in the absence of average bias of the parameters [2]. Moreover, it has been shown that in the adiabatic limit, this pumping current has a geometrical interpretation, and it can be expressed as a line integral in the space of the modulation parameters [3,4].
    Motivated by these results, in the present study, a Thouless pump obeying a non-Markovian master equation is mapped onto a larger Markovian system and analysed theoretically. We demonstrate that a good agreement is achieved between the pumping current obtained from the numerical solution, and the analytically calculated geometrical current in the adiabatic limit. Furthermore, we employ a technique based on eigenvalue analysis and perturbation theory to go beyond the adiabatic limit and show the improvement on the analytical calculation that results from accounting for the effect of finite modulation speed [5].
  • Reference
    [1] H.-P Breuer et al., Rev. Mod. Phys. 88, 021002 (2016).
    [2] D. J. Thouless, Phys Rev B 27, 6083 (1983).
    [3] M. V. Berry. Proc. R. Soc. London, Series A 392, 45 (1984).
    [4] N. A. Sinitsyn and I. Nemenman, Europhys. Lett. 77, 58001 (2007).
    [5] V. M. M. Paasonen and H. Hayakawa, Phys. Rev. Res. 3, 023238 (2021).
• Rheology and Diffusivity of Sheared Glasses - Perspective from the non-eq. criticality【Zoom】
  • Norihiro Oyama (Department of Basics Science, Univ. of Tokyo)
  • Date: 2021/06/02 16:00 --
  • Place: ZOOM*
    *People interested in attending the seminar should register with google form.
  • Abstract:
    The Herschel-Bulkley law[1], a universal constitutive relation, has been empirically known to be applicable to a vast range of soft materials, such as foams, suspensions, emulsions, glasses, and even biological systems like blood and vegetables[2]. Although we can naively expect that the macroscopic material properties are governed by the microscopic structures, the structural origin of the Herschel-Bulkley law has remained an open question.
    By means of atomistic simulation of binary Lennard-Jones glasses, we found that the instantaneous normal modes with negative eigenvalues, or so-called imaginary modes, serve as the structural signatures for the Herschel-Bulkley rheology in sheared glasses[3].
    In this seminar, the speaker explains how the imaginary modes can be regarded as the structural signatures based on the nonequilibrium criticality of the yielding transition[4], which governs the fluidization of sheared glasses.
    Also, the instantaneous normal modes analysis can account for the scaling behaviors of the particle diffusion that are induced by the applied shear[5]. In particular, the speaker presents that the diffusion dynamics is governed by another length scale than that for the rheological responses and discusses the possible mechanism for such a difference.
  • Reference
    [1]Herschel and Bulkley, Kolloid-Zeitschrift 39, 291 (1926)
    [2]Bonn et al., Rev. Mod. Phys. 89, 035005 (2017)
    [3] Oyama, Mizuno, and Ikeda, arxiv:2011.12568 (2020)
    [4]Lin et al., Proc. Natl. Acad. Sci. 111, 14382 (2014)
    [5] Ouama, in preparation
• Numerical simulations of entropy production in open quantum theory: Boltzmann entropy vs von Neumann entropy
  • Soichi Sakamoto (Institute for Molecular Science)
  • Date: 2021/04/14 16:00 --
  • Place: K206, Main Building, Yukawa Institute, Kyoto U.
    ＊It will be held on-site.
  • Abstract:
    In thermodynamics and statistical mechanics, entropy is an important metric representing the time-reversible dynamics of an isolated system. The second law of thermodynamics states that entropy production is always positive whereas it is zero if the dynamics are reversible. In a quantum system coupled to a heat bath, the entropy production evaluated from the von Neumann entropy is proven to be always positive if the system and the bath are factorized at the initial time. However, this entropy production can be used only in the case of the weak system-bath interaction, because the contribution of this interaction to the entropy production is neglected. In this seminar, we present a scheme to evaluate various thermodynamic functions in an open quantum system under a time-dependent external field.[1] We introduce the free energy and the “Boltzmann” entropy for an isothermal process on the basis of open quantum regime. Employing the hierarchical equations of motion,[2] we examine the role of the interaction in entropy production by computing the Boltzmann entropy and the von Neumann for various values of the system-bath coupling strength. If the initial state of the system is chosen to be the thermal equilibrium state of the total system, we will finally find that the entropy production with the Boltzmann entropy is always positive, while that with the von Neumann entropy becomes negative even in the weak interaction.
  • Reference
    [1]S. Sakamoto and Y. Tanimura, J. Chem. Phys. 153, 234107 (2020).
    [2]Y. Tanimura, J. Chem. Phys. 153, 020901 (2020).
• Dynamic friction of soft solids at subsonic and intersonic sliding velocities【Zoom】
  • Tetsuo Yamaguchi (The University of Tokyo)
  • Date: 2021/04/07 16:00 --
  • Place: ZOOM*
    *People interested in attending the seminar should register with google form.
  • Abstract:
    The frictional contact between two cylinders or spheres forms mild elastic deformation and smooth contact pressure profiles, known as Hertzian contact, when the sliding velocity is small enough[1]. However, little was known about the sliding behavior at the sliding velocities larger than the elastic wave velocities of the solids. In this study, we conducted friction experiments between a compliant gel and a rigid cylinder at sliding velocities comparable to the Rayleigh wave or Secondary wave velocity of the gel[2]. As a result, we succeeded, for the first time, in observing abnormal frictional behavior: when the sliding velocity exceeds the wave velocities, the contact state transitions from Hertzian like to flat punch like, resulting in the abrupt increase in the friction coefficient. We also succeeded in deriving theoretical solutions for the contact pressure distributions and the deformation profiles in the presence of friction, which are consistent with our experimental observations.
  • Reference
    [1] K. L. Johnson, Contact Mechanics, Cambridge University Press, Cambridge (1985).
    [2] T. Yashiki, T. Morita, Y. Sawae, and T. Yamaguchi, Subsonic to Intersonic Transition in Sliding Friction for Soft Solids, Physical Review Letters 124 (23), 238001 (2020).