TY - JOUR T1 - Coulomb bound states of strongly interacting photons JF - Physical Review Letters Y1 - 2015 A1 - Mohammad F. Maghrebi A1 - Michael Gullans A1 - P. Bienias A1 - S. Choi A1 - I. Martin A1 - O. Firstenberg A1 - M. D. Lukin A1 - H. P. Büchler A1 - Alexey V. Gorshkov AB - We 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 quasi-bound 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 wavefunction 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. VL - 115 U4 - 123601 UR - http://arxiv.org/abs/1505.03859v1 CP - 12 J1 - Phys. Rev. Lett. U5 - 10.1103/PhysRevLett.115.123601 ER -