Non-equilibrium Transport of Light

Rishabh Jha

Youqi Ke, Sheng Meng, Ke Xia +1 more

Under external driving forces, the system deviates from the equilibrium distribution and enters a non-equilibrium state, resulting in transport phenomena of both charge and energy and the emergence of many novel non-equilibrium phases. The transport of charge and energy through a quantum many-body material system is a fundamental process in the conversion and storage of energy and information, and material properties can undergo significant changes at the far-from-equilibrium conditions. A deep understanding and accurate calculation of non-equilibrium states in materials and devices, including transport properties, are essential for enhancing the control of material properties and advancing the related manufacturing technologies, constituting a key aspect of condensed matter physics and computational physics.

M Ridley, N. Walter Talarico, Daniel Karlsson +2 more

Abstract We review one of the most versatile theoretical approaches to the study of time-dependent correlated quantum transport in nano-systems: the non-equilibrium Green’s function (NEGF) formalism. Within this formalism, one can treat, on the same footing, inter-particle interactions, external drives and/or perturbations, and coupling to baths with a (piece-wise) continuum set of degrees of freedom. After a historical overview on the theory of transport in quantum systems, we present a modern introduction of the NEGF approach to quantum transport. We discuss the inclusion of inter-particle interactions using diagrammatic techniques, and the use of the so-called embedding and inbedding techniques which take the bath couplings into account non-perturbatively. In various limits, such as the non-interacting limit and the steady-state limit, we then show how the NEGF formalism elegantly reduces to well-known formulae in quantum transport as special cases. We then discuss non-equilibrium transport in general, for both particle and energy currents. Under the presence of a time-dependent drive—encompassing pump–probe scenarios as well as driven quantum systems—we discuss the transient as well as asymptotic behavior, and also how to use NEGF to infer information on the out-of-equilibrium system. As illustrative examples, we consider model systems general enough to pave the way to realistic systems. These examples encompass one- and two-dimensional electronic systems, systems with electron–phonon couplings, topological superconductors, and optically responsive molecular junctions where electron–photon couplings are relevant.

William T. B. Malouf, John Goold, Gerardo Adesso +1 more

Non-equilibrium steady-states are characterized by the existence of macroscopic heat currents flowing between two or more reservoirs. However, the existence of these currents also implies that information is constantly being transmitted from one reservoir to the other. In this letter we address the transport of information in the context of quantum non-equilibrium steady states. We first show how the ability of the excitations to transfer information can be quantified by the conditional mutual information (CMI), a more general measure of tripartite correlations. We then apply this to an exactly soluble model allowing for both ballistic and diffusive behavior. Our approach allows us to compute the CMI for arbitrary sizes and thus find the scaling rules connecting information transport and diffusivity. Finally, we discuss how this new perspective in the characterization of non-equilibrium systems may be applied to understand the issue of local equilibration in non-equilibrium states.