Coherent Scattering of Radiation and Negative Energy States

Xiaomin Hu

The exponentially decaying semi-stationary states of an assembly of identical classical radiators can have decay rates and resonant frequencies significantly different from that of an isolated radiator. These coherent effects on classical radiators emitting classical waves apply also to the particle processes in quantum limits, leading to the superradiant and subradiant modes with widths(decay rates) greatly enhanced or suppressed and resonant energies significantly shifted. The purpose of this thesis is to investigate these coherent effects on slow neutron-heavy nuclei interaction. A simple field model is introduced to show the coherent effects on the decay rates and resonant energies of two identical decaying states and on the neutron widths and resonant energies of neutron-two nuclei scattering. The latter case is also obtained by multiple scattering theory and is extended to a more general case of neutron-N nuclei scattering. The coherent effects on neutron width near Bragg angle in a crystal are also investigated.

M. J. Beranro, John B. DeVelis, A. S. Marathay

Kian Hwee Lim, Kiarn T. Laverick, Sahil S. Jafar +3 more

Wigner negativity is a key resource for quantum technologies but is difficult to optimize in multimode scattering systems. We study the scattering of coherent pulses by a two-level emitter coupled to a one-dimensional waveguide and introduce energetic cost functions that enable the optimization of Wigner negativity without reconstructing the full Wigner function. By decomposing the scattered energy into coherent, thermal, squeezing, and non-Gaussian contributions, we identify an energetic witness that strongly correlates with the achievable negativity across all driving regimes. This approach singles out optimal output temporal modes and uncovers operating points generating appreciable Wigner negativity with sub-photon input energies. We further identify a maximal energy-efficiency regime at spectral mode matching, where the emitter effectively implements a vacuum-selective $π$ phase shift, realizing a giant optical nonlinearity. These results establish energetic optimization as a practical route to engineering Wigner-negative photonic states in waveguide quantum electrodynamics and related bosonic scattering platforms.

A. D. Gazazyan

K. J. Le Couteur, S. Zienau

It is proved that the difference between the single electron theory and the positron theory for the coherent scattering of light by an atom represents the scattering of light by the atomic potential. In the practical cases the effect is negligible. The gauge invariance of the perturbation formulae for this effect is discussed.

Zoltan Fried, Lloyd C. Kannenberg