In this talk I discuss the idea of nonequilibrium Green's functions (NEGF) and recent theoretical and computational results. I will start by introducing the real-time (Keldysh) Green's functions for a many-body system of bosons or fermions and their equations of motion - the Keldysh-Kadanoff-Baym equations (KBE). Their main advantage is that they guarantee the relevant conservation laws, are applicable to fields of arbitrary intensity as well as to arbitrarily short pulses. There are two main lines of research:
1. Use the KBE to derive general quantum kinetic equations for the Wigner function or density matrix. These equations contain collisions including nonlinear field effects, finite collision durations etc. I will illustrate this by examples from dense laser plasmas.
2. Direct solution of the KBE for the two-time NEGF. Here numerical results were obtained for the correlated electron gas and for electron-hole plasmas in semiconductors in excited by optical pulses. These results can directly be extended to small atoms interacting with short x-ray pulses. Here first results have been obtained by our group, in particular by my affiliate Karsten Balzer. I will give a brief overview and discuss the capabilities of this method.
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(View notes on density operator.)
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