7.5.2020 Theoretical and numerical studies of the dynamics of open quantum systems (Agasti)

The time-adaptive density matrix renormalization group (t-DMRG) is considered as one of the most powerful methods to study strongly-correlated many-body quantum system. In his doctoral thesis at the University of Jyväskyla, along with the theoretical modeling, Souvik Agasti implemented DMRG numerical scheme for the simulation of canonical system-environment model by mapping it to one dimensional harmonic chain.
Published
7.5.2020

Open quantum systems have drawn attention over the decades because of their applicability in the foundation of statistical mechanics, quantum mechanics, and the realization of optical, atomic and molecular physics. Considering analytical techniques, quantum Langevin and master equation are widely used to study the time dynamics and the steady state behavior of open quantum systems.

Even though the theories developed in the context of open quantum systems have proven powerful tools, they do not provide a satisfactory platform to analyze nonlinear coupling between the system and environment. The interesting effects are often overlooked when we cannot handle the interaction between two systems in a perturbative manner. The limitation of the analytics explicitly provokes us to simulate the time evolution numerically.

On theoretical point of view, the thesis presents an analytical technique for a given form of the nonlinear system-environment coupling, therefore provides a general platform for engineering potentially interesting quantum-dynamical models for open quantum systems. The numerical work is important from two aspects: on the one hand, it shows how to use the DMRG numerical technique as a new constructive method, for the generation of thermal bath and the time evolution of the system in the presence of the thermal bath, and the simulation of Kerr nonlinear systems and analyzing non-classical dynamics. On the other hand, it presents a comparative study and checks the consistency with the well established quantum Langevin and master equation, highlighting advantage and disadvantages, and therefore the applicability of the new novel numerical technique.

"On general grounds, developments of techniques to study the dynamical and steady state behavior of nonlinear systems, are the fundamental aspect of quantum physics. I believe my approach of dealing with nonlinearities has a vast range of application in the physics of quantum communication, sensing electromagnetic fields and detecting gravitational waves", says Souvik Agasti.

The dissertation is published in JYU Dissertations series, number 215, Jyväskylä, 2020. ISBN 978-951-39-8149-5 (PDF)
URN:ISBN:978-951-39-8149-5, ISSN 2489-9003 
Link to the publication: 

M.Tech. Souvik Agasti defends his doctoral dissertation in Physics "Theoretical and numerical studies of the dynamics of open quantum systems" at the Ä¢¹½Ö±²¥ on Thursday 7th of may 2020 at the Department of Physics starting at 12. The Opponent Associate Professor is André Xuereb from University of Malta and Custos is Docent Pekka Koskinen from the Ä¢¹½Ö±²¥. The doctoral dissertation is held in English.

The audience can follow the dissertation event online with Zoom Video Webinar, link to the webinar:
Meeting ID: 674 3255 9169