Maghrebi, M. F.Gullans, M. J.Bienias, P.Choi, SoonwonMartin, I.Firstenberg, O.Lukin, MikhailBüchler, H. P.Gorshkov, A. V.2016-07-222015Maghrebi, M. F., M. J. Gullans, P. Bienias, S. Choi, I. Martin, O. Firstenberg, M. D. Lukin, H. P. Büchler, and A. V. Gorshkov. 2015. “Coulomb Bound States of Strongly Interacting Photons.” Physical Review Letters 115 (12) (September). doi:10.1103/physrevlett.115.123601.0031-9007http://nrs.harvard.edu/urn-3:HUL.InstRepos:27729288We show that two photons coupled to Rydberg states via electromagnetically induced transparency can interact via an effective Coulomb potential. This interaction gives rise to a continuum of two-body bound states. Within the continuum, metastable bound states are distinguished in analogy with quasibound states tunneling through a potential barrier. We find multiple branches of metastable bound states whose energy spectrum is governed by the Coulomb potential, thus obtaining a photonic analogue of the hydrogen atom. Under certain conditions, the wave function resembles that of a diatomic molecule in which the two polaritons are separated by a finite “bond length.” These states propagate with a negative group velocity in the medium, allowing for a simple preparation and detection scheme, before they slowly decay to pairs of bound Rydberg atoms.en-USJournal Article2016-07-2210.1103/PhysRevLett.115.123601