Motivated by the Jaynes-Cummings (JC) model, we consider here a quantum dot coupled simultaneously to a reservoir of photons and two electric leads (free-fermion reservoirs). This new Jaynes-Cummings-leads (JCL)-type model makes it possible that the fermion current through the dot creates a photon flux, which describes a light-emitting device. The same model also describes a transformation of the photon flux into the current of fermions, i.e., a quantum dot light-absorbing device. The key tool

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... o obtain these results is the abstract Landauer-Büttiker formula. Dedicated to the memory of Pierre Duclos H. Neidhardt, L. Wilhelm, and V.A. Zagrebnov induced component is not, c.f. Sec. 5.1. In this case, the flux of photons J ph out of the quantum dot (sample) is also non-zero, i.e., the dot serves as a light emitting device, c.f. Sec. 5.2. In general, J ph = 0 only when the photon-induced component is not zero, i.e. J ph el = 0. It turns out that when choosing the parameters of the model in a suitable manner, one gets either a photon emitting or a photon absorbing system. Hence the JCL-model can be used either as a light emission device or as a light-cell. The proofs of explicit formulas for the fermion and photon currents, J el , J ph , are the contents of Secs. 4 and 5. Note that the JCL-model is called mirror symmetric if (roughly speaking) one can interchange the left and the right leads and the JCL-model remains unchanged. In Sec. 5, we discuss a surprising example of a mirror symmetric JCL-model in which the free-fermion current is zero but the model is photon emitting. This peculiarity is due to a specific choice of the photon-electron interaction which produces fermions with internal harmonic degrees of freedom.