Single photons by quenching the vacuum
9 pags., 10 figs. ; Heisenberg's uncertainty principle implies that the quantum vacuum is not empty but fluctuates. These fluctuations can be converted into radiation through nonadiabatic changes in the Hamiltonian. Here, we discuss how to control this vacuum radiation, engineering a single-photon emitter out of a two-level system (2LS) ultrastrongly coupled to a finite-band waveguide in a vacuum state. More precisely, we show the 2LS nonlinearity shapes the vacuum radiation into a non-Gaussian superposition of even and odd cat states. When the 2LS bare frequency lays within the band gaps, this emission can be well approximated by individual photons. This picture is confirmed by a characterization of the ground and bound states, and a study of the dynamics with matrix-product states and polaron Hamiltonian methods. ; We acknowledge the Spanish Ministerio de Ciencia, Innovación y Universidades within project MAT2017-88358-C3-1-R and FIS2015-70856-P and the Aragón Government project Q-MAD and CAM PRICYT Research Network QUITEMAD+ S2013/ICE2801. EU-QUANTERA project SUMO is also acknow edged. Eduardo Sánchez-Burillo acknowledges ERC Advanced Grant QENOCOBA under the EU Horizon 2020 program (grant agreement 742102).
