We develop a general approach to describe the scattering of quantum light by a lossy macroscopic object placed in vacuum with no restrictions on both its dispersive optical response and its spatially inhomogeneous composition. Our analysis is based on the modified Langevin noise formalism, a recently introduced version of macroscopic quantum electrodynamics where scattering $s$ modes are explicitly separated from electric $e$ and magnetic $m$ medium excitations; accordingly the formalism involves three kinds of noninteracting boson polaritons such that, in the lossless limit, $s$ polaritons reduce to standard photons whereas $e$ and $m$ polaritons disappear. We analytically derive the input-output unitary relation joining the boson operators of the ingoing and outgoing polaritons, a nontrivial result hinging upon original relations which comprehensively describe the transmission-emission-absorption interplay pertaining the classical radiation scattering, relations we here deduce by resorting to properties of the dyadic Green's function. Besides we exploit the input-output relation to connect the output state of the field to the input one, this unveiling the role played by various classical electromagnetic dyadics in quantum optical scattering. We specialize the discussion to the most common situation where the object is initially not electromagnetically excited, with the ingoing electromagnetic state only containing $s$ polaritons, and we analyze the impact of the classical transmission and absorption dyadics on the transitions from ingoing to outgoing $s$ polaritons and on the creation of outgoing $e$ and $m$ polaritons, respectively. Since the scattered radiation is collected in the far-field and the object is usually left unmeasured, we analytically derive the reduced density operator of the outgoing $s$ polaritons revealing, in particular, how object losses both produce quantum decoherence of the scattered radiation and enable to exploit the possible entanglement among ingoing $s$ polaritons to dramatically manipulate the statistical mixture of the quantum states pertaining to the scattered radiation.

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• Quantum interference effects
• Quantum optics
• Wave scattering