Effects from Additional Random Configuration to Linear Response and Modified Fluctuation-Dissipation Relation

TL;DR

This paper investigates how additional random, time-dependent external potentials modify the linear response and fluctuation-dissipation relations in quantum systems, revealing extra contributions from randomness and memory effects.

Contribution

It introduces a modified fluctuation-dissipation relation accounting for randomness and memory effects in systems with random external potentials.

Findings

Derived a generalized response formula incorporating randomness.

Demonstrated the impact of time-dependent randomness on fluctuation-dissipation.

Showed modifications to the Kubo formula due to external random potentials.

Abstract

In this work, a physical system described by Hamiltonian $\mathbf{H}_\omega = \mathbf{H}_0 + \mathbf{V}_\omega(\mathbf{x},t)$ consisted of a solvable model $\mathbf{H}$ and external random and time-dependent potential $\mathbf{V}_\omega(\mathbf{x},t)$ is investigated. Under the conditions that the average external potential with respect to the configuration $\omega$ is constant in time, and, for each configuration, the potential changes smoothly that the evolution of the system follows Schr\"odinger dynamics, the mean-dynamics can be derived from taking average of the equation with respect to configuration parameter $\omega$. It provides extra contributions from the deviations of the Hamiltonian and evolved state along the time to the Heisenberg and Liouville-von Neumann equations. Consequently, the Kubo's formula and the fluctuation-dissipation relation obtained from the construction is modified in the sense that the contribution from the information of randomness and memory effect from time-dependence are present.