One molecule, one photon

Rezus, Walt, Zumofen +3 more

Karl Otto Greulich

Throughout the development and confirmation of the photon concept, "Gedankenexperiments" have been invoked where a light source is attenuated until "only one photon is in the apparatus." Such a statement requires, however, knowledge on details of the light generation process, which were not known until the advent of true single-photon light sources such as isolated single atoms or molecules. Here, starting from a two atom light source, it is shown that probably multi-atom or multi-molecule light sources do not generate, even not in small fractions, antibunching photons and that attenuation down to one photon per time unit is not reliably possible. Thus, one of the strongest arguments in favour of the existence of single "photons" in free space, the accumulation time argument, which discusses the absorption of a single photon by a single atom or molecule, becomes questionable.

Anonymous

Michael R. Philpott

The two-photon transitions of a system of two dissimilar molecules are studied in the dipole approximation. Special attention is paid to transitions in which both molecules participate simultaneously. By use of a reduced Hamiltonian the influence of long-range intermolecular forces is also studied. The three main transitions considered occur when: (i) no molecular level is in resonance with a primary photon, (ii) one primary photon excites a molecular level, and (iii) two primary photons excite a molecular level. It is shown that in no case can the mixing of excited states by intermolecular forces be represented as a change to an effective transition dipole moment for one of the molecules. The one-photon decay of a state in which both molecules are excited is also treated.

R. Lettow, Yves L. A. Rezus, Alois Renn +4 more

We demonstrate two-photon interference using two remote single molecules as bright solid-state sources of indistinguishable photons. By varying the transition frequency and spectral width of one molecule, we tune and explore the effect of photon distinguishability. We discuss future improvements on the brightness of single-photon beams, their integration by large numbers on chips, and the extension of our experimental scheme to coupling and entanglement of distant molecules.