ELFT HÍRADÓ

[tcsaba <tcsaba AT eik.bme.hu>]

                 M E G H Í V Ó - I N V I T A T I O N

    Seminar Series of the Department of Theoretical Physics at the
           Budapest University of Technology and Economics


                        Alexandra Nagy
             (École Polytechnique Fédérale de Lausanne)


     Numerical approaches to the master equation of open quantum systems


The study of the non-equilibrium dynamics of many-body open quantum 
systems has attracted increasing attention in recent years, due to the 
progress in several experimental areas. The time evolution of these 
systems is dictated by the Liouville-von-Neumann master equation which 
considers the interplay between the Hamiltonian dynamics of the system 
and the driven-dissipative processes. Typically, this dynamics leads to 
a non-equilibrium steady state for which a multitude of novel phenomena 
are expected, including the emergence of dissipative phase transitions. 
However, the theoretical modeling of out of equilibrium systems presents 
a major challenge since the computational eort scales exponentially with 
the system size. The study of these systems calls for the development of 
new eective methods.

In this talk I will discuss novel numerical techniques to the modeling 
of open many-body quantum systems. Firstly, I will present the Driven 
Dissipative Quantum Monte Carlo approach, a real-time pro- jector Monte 
Carlo method to stochastically sample the master equation. I demonstrate 
the eciency of our approach by applying it to the driven-dissipative 
two-dimensional spin lattice governed by the Heisenberg XYZ Hamiltonian.

Finally, I will also discuss some preliminary results on a variational 
approach based on the minimization of a suitable norm of the quantum 
master equation. I apply this method to the driven-dissipative one 
dimensional Bose-Hubbard model showing how the choice of the variational 
ansatz for the density matrix effects the accuracy of the steady state 
expectation values of certain observables.


Időpont: 2018. május 18. péntek, 10:15
Helyszín: BME Fizikai Intézet, Elméleti Fizika Tanszék,
Budafoki út 8. F-épület, III lépcsőház, szemináriumi szoba