Abstract

Various transport and optical properties of quantum devices require an account of significant coupling to their electronic or photonic environments. In such cases, approximation strategies are necessary that go beyond the celebrated weak-coupling, memoryless master equations (Lindblad dynamical semigroups). However, already for stationary properties the perturbative calculation of corrections due to environment coupling are quite involved and are fraught with dangers when local interactions are strong. Dynamical properties further complicate the matter by requiring an account of “memory effects”.

In the first part of my talk I will introduce and review some of these issues from the general perspective of open-system dynamics. I will highlight how insights from quantum information about density operators and their dynamics may clarify, guide and motivate the application of statistical field theoretical techniques to this problem. This is illustrated by two simple solvable models of electron transport and dissipative Jaynes-Cummings dynamics, respectively.

In the second part of my talk I will discuss the remarkable fact that the open quantum system can be equivalently described by two exact, but fundamentally different equations of motion. This puzzling issue is resolved by an elegant “fixed-point” relation between the system’s time-nonlocal memory-kernel and its time-local generator (time-convolutionless). This result allows several puzzles surrounding “memory effects” to be resolved and provides an intriguing new approach to iteratively compute them.

References:
V. Reimer, M. R Wegewijs, SciPost Phys. 7, 012 (2019)
K. Nestmann, V. Bruch, M. R. Wegewijs, Phys. Rev. X 11, 021041 (2021)
K. Nestmann, M. R. Wegewijs, Phys. Rev. B 104, 155407 (2021)
K. Nestmann, M. R. Wegewijs, SciPost Phys. 12, 121 (2022)
K. Nestmann, M. Leijnse, M. R. Wegewijs, J. Chem. Phys. 161 (2024)