Ground-State Dressing and Delayed Feedback of a Chiral Giant Atom in Ultrastrong Waveguide QED

arXiv:2611.07036v1 Announce Type: new Abstract: We study a chiral giant atom ultrastrongly coupled to a one-dimensional waveguide at two spatially separated points. At a relative coupling phase \pi/2, the total spectral density is independent of the distance between the coupling points, whereas its directional components are not. Using a variational polaron transformation, we show that the renormalized transition frequency and the total ground-state dressing inherit this independence, while the virtual-photon cloud remains chiral. A sudden switch-off of the coupling releases this cloud as directional radiation.