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  • 1.
    Borlenghi, Simone
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Boman, Magnus
    KTH, School of Electrical Engineering and Computer Science (EECS), Software and Computer systems, SCS. RISE SICS, Electrum 229, SE-16429 Kista, Sweden..
    Delin, Anna
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics. KTH, Centres, SeRC - Swedish e-Science Research Centre.
    Modeling reservoir computing with the discrete nonlinear Schrodinger equation2018In: Physical review. E, ISSN 2470-0045, E-ISSN 2470-0053, Vol. 98, no 5, article id 052101Article in journal (Refereed)
    Abstract [en]

    We formulate, using the discrete nonlinear Schrodinger equation (DNLS), a general approach to encode and process information based on reservoir computing. Reservoir computing is a promising avenue for realizing neuromorphic computing devices. In such computing systems, training is performed only at the output level by adjusting the output from the reservoir with respect to a target signal. In our formulation, the reservoir can be an arbitrary physical system, driven out of thermal equilibrium by an external driving. The DNLS is a general oscillator model with broad application in physics, and we argue that our approach is completely general and does not depend on the physical realization of the reservoir. The driving, which encodes the object to be recognized, acts as a thermodynamic force, one for each node in the reservoir. Currents associated with these thermodynamic forces in turn encode the output signal from the reservoir. As an example, we consider numerically the problem of supervised learning for pattern recognition, using as a reservoir a network of nonlinear oscillators.

  • 2.
    Borlenghi, Simone
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Delin, Anna
    KTH, Centres, SeRC - Swedish e-Science Research Centre. KTH, School of Engineering Sciences (SCI), Applied Physics.
    Stochastic Thermodynamics of Oscillators' Networks2018In: Entropy, ISSN 1099-4300, E-ISSN 1099-4300, Vol. 20, no 12, article id 992Article in journal (Refereed)
    Abstract [en]

    We apply the stochastic thermodynamics formalism to describe the dynamics of systems of complex Langevin and Fokker-Planck equations. We provide in particular a simple and general recipe to calculate thermodynamical currents, dissipated and propagating heat for networks of nonlinear oscillators. By using the Hodge decomposition of thermodynamical forces and fluxes, we derive a formula for entropy production that generalises the notion of non-potential forces and makes transparent the breaking of detailed balance and of time reversal symmetry for states arbitrarily far from equilibrium. Our formalism is then applied to describe the off-equilibrium thermodynamics of a few examples, notably a continuum ferromagnet, a network of classical spin-oscillators and the Frenkel-Kontorova model of nano friction.

  • 3.
    Borlenghi, Simone
    et al.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics. Uppsala University, Sweden.
    Iubini, Stefano
    Lepri, Stefano
    Bergqvist, Lars
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics.
    Delin, Anna
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics. Uppsala University, Sweden.
    Fransson, Jonas
    Coherent energy transport in classical nonlinear oscillators: An analogy with the Josephson effect2015In: Physical Review E. Statistical, Nonlinear, and Soft Matter Physics, ISSN 1539-3755, E-ISSN 1550-2376, Vol. 91, no 4, article id 040102Article in journal (Refereed)
    Abstract [en]

    By means of a simple theoretical model and numerical simulations, we demonstrate the presence of persistent energy currents in a lattice of classical nonlinear oscillators with uniform temperature and chemical potential. In analogy with the well-known Josephson effect, the currents are proportional to the sine of the phase differences between the oscillators. Our results elucidate general aspects of nonequilibrium thermodynamics and point towards a way to practically control transport phenomena in a large class of systems. We apply the model to describe the phase-controlled spin-wave current in a bilayer nanopillar.

  • 4.
    Borlenghi, Simone
    et al.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics. Uppsala University, Sweden.
    Iubini, Stefano
    Lepri, Stefano
    Chico, Jonathan
    Bergqvist, Lars
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Delin, Anna
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF. Uppsala University, Sweden.
    Fransson, Jonas
    Energy and magnetization transport in nonequilibrium macrospin systems2015In: Physical Review E. Statistical, Nonlinear, and Soft Matter Physics, ISSN 1539-3755, E-ISSN 1550-2376, Vol. 92, no 1, article id 012116Article in journal (Refereed)
    Abstract [en]

    We investigate numerically the magnetization dynamics of an array of nanodisks interacting through the magnetodipolar coupling. In the presence of a temperature gradient, the chain reaches a nonequilibrium steady state where energy and magnetization currents propagate. This effect can be described as the flow of energy and particle currents in an off-equilibrium discrete nonlinear Schrodinger (DNLS) equation. This model makes transparent the transport properties of the system and allows for a precise definition of temperature and chemical potential for a precessing spin. The present study proposes a setup for the spin-Seebeck effect, and shows that its qualitative features can be captured by a general oscillator-chain model.

  • 5.
    Borlenghi, Simone
    et al.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics.
    Lepri, Stefano
    Bergqvist, Lars
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF. KTH, Centres, SeRC - Swedish e-Science Research Centre.
    Delin, Anna
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Thermomagnonic diode: Rectification of energy and magnetization currents2014In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 89, no 5, p. 054428-Article in journal (Refereed)
    Abstract [en]

    We investigate the dynamics of two coupled macrospins connected to thermal baths at different temperatures. The system behaves like a diode which allows the propagation of energy and magnetization currents in one direction only. This effect is described by a simple model of two coupled nonlinear oscillators interacting with two independent reservoirs. It is shown that the rectification phenomenon can be interpreted as a a stochastic phase synchronization of the two spin oscillators. A brief comparison with realistic micromagnetic simulations is presented. This new effect yields promising opportunities in spin caloritronics and nanophononic devices.

  • 6.
    Borlenghi, Simone
    et al.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Wang, Weiwei
    Fangohr, Hans
    Bergqvist, Lars
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF. KTH, Centres, SeRC - Swedish e-Science Research Centre.
    Delin, Anna
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF. KTH, Centres, SeRC - Swedish e-Science Research Centre.
    Designing a Spin-Seebeck Diode2014In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 112, no 4, p. 047203-Article in journal (Refereed)
    Abstract [en]

    Using micromagnetic simulations, we have investigated spin dynamics in a spin-valve bilayer in the presence of a thermal gradient. The direction and the intensity of the gradient allow us to excite the spin wave modes of each layer selectively. This permits us to synchronize the magnetization precession of the two layers and to rectify the flows of energy and magnetization through the system. Our study yields promising opportunities for applications in spin caloritronics and nanophononics devices.

1 - 6 of 6
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