4pm - 5pm GMT

Wednesday 24 November 2021

Quantum Brownian motion for magnets

The speaker is a theoretical physicist and world expert in the exciting new fields of quantum information theory and quantum thermodynamics. The talk will be of interest to those working in the general area of open quantum systems.


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This seminar is by invitation only. A Zoom link will be sent to participants before the event.


  • Janet Anders


In this talk Janet Anders will discuss how a system+bath Hamiltonian, similar to the Caldeira-Leggett and spin-boson models, can be used to derive a general spin dynamics equation [1]. Janet will show how in the Ohmic (Markovian) limit the new equation reduces to the Landau Lifshitz Gilbert equation, a phenomenological equation widely used in magnetism.

Janet will demonstrate how resonant Lorentzian couplings can be used as a general tool for the systematic comparison of spin dynamics of Markovian and non-Markovian regimes, and present numerical results of a classical spin's dynamics under classical and quantum noise. We find much quicker decay to steady state for couplings that invoke memory effects, and quantum flattening of the magnetization curve at low temperatures.

In the second part of the talk we will explore long time steady states. The dynamical convergence to the Gibbs state is a standard assumption across much of classical and quantum thermodynamics. However, for nanoscale and quantum systems the interaction with their environment becomes non-negligible.  Is the system steady state then still the Gibbs state? And if not, how exactly does it depend on the interaction details? Janet will briefly outline several aspects of this timely topic [2, 3, 4].


  1. Quantum Brownian Motion for Magnets, J Anders, C Sait, S Horsley, arxiv 2009.00600 (2020)
  2. Weak and ultrastrong coupling limits of the quantum mean force Gibbs state, arXiv:2104.12606 to be published in PRL, JD Cresser, J Anders
  3. Open quantum system dynamics and the mean force Gibbs state,  arXiv:2110.01671, M Merkli, AS Trushechkin, JD Cresser, J Anders
  4. Quantum-classical transition of steady states and mean force Gibbs states in the spin boson model, in prep, F Cerisola, M Berritta, S Scali, JD Cresser, SAR Horsley, J Anders.


Janet Anders

Janet studied physics at the University of Potsdam in Germany and completed her PhD in quantum information theory at the National University of Singapore. In 2007 she joined University College London as a postdoc with a rather too brief contract and was lucky to be awarded a prestigious Dorothy Hodgkin research fellowship in 2009 by the Royal Society. She took up a lecturer position at the University of Exeter in 2013, and now leads the Quantum Non-equilibrium group and the Theoretical Physics theme at the University of Exeter. Since 2019 she splits her time between Exeter and the University of Potsdam.

Janet’s research interests lie in the wider area of quantum thermodynamics, including the concept of work in quantum mechanics, strong coupling thermodynamics, properties of open quantum and classical systems, classical Brownian motion and stochastic thermodynamics for biophysics applications. Janet was awarded the Institute of Physics Bates Prize in 2015, and an EPSRC early career fellowship in 2018.

Related information

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