A Single Atom Antenna
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In radio technology antennas are used to efficiently collect energy from the electromagnetic field. In the optical regime nanoscale antennas have been developed and in nature specialized antenna molecules efficiently collect visible light to power biochemical reactions. Schematically all these systems consist of the antenna itself which couples to the radiation field, a receiver which uses the energy and a route to transport the energy between them. Here we demonstrate the smallest possible implementation of such an antenna-receiver complex which consists of a single (Helium) atom acting as the antenna and a second (Neon) atom acting as a receiver. In this most simple antenna/receiver setup the antenna atom enhances the coupling to the radiation field by more than a factor of 60. After being collected by the antenna the energy is transferred to the receiver via interatomic Coulombic decay (ICD). Our measurements furthermore reveal the transfer time to be 130 – 1100 fsec, depending on the vibrational quantum state, thus providing a direct measurement of the decay time of ICD. 
Fig. 1: Schematic of the antenna mechanism. Here, we use He as an antenna atom and Ne as the receiver. 
Fig. 2: Photoionization of a supersonic jet containing He (80%) and Ne (20%) and about 3.2% HeNe dimers. (a) Ion time of flight versus photon energy in the vicinity of the He(1s3p) resonance. (b) Ion time of flight for the photon energy range 23.0805-23.0815 eV (on resonance). (c) Ion time of flight for the photon energy range 23.0305-23.0315 eV (off resonance). 
Fig. 3: HeNe+ photoion yield as a function of photon energy in the vicinity of the He(1s3p) resonance. 
Fig. 4: Potential energy curves of the excited states of HeNe and the natural orbitals of the excited electron at R = 3.04 Å. The atom on the right is He. In conclusion, we have experimentally shown that a single atom can act as a highly efficient antenna to absorb energy from a light field and pass the energy to a neighboring receiver atom within a few hundreds of femtoseconds. The vibrationally resolved measurement of the resonance width for a selected electronic state provides a benchmark for future calculations of the underlying energy transfer mechanism of ICD. Our findings yield (to our knowledge) the first vibrationally resolved lifetimes of ICD after narrow band excitation. Publication:
F. Trinter, J. B. Williams, M. Weller, M. Waitz, M. Pitzer, J. Voigtsberger, C. Schober, G. Kastirke, C. Müller, C. Goihl, P. Burzynski, F. Wiegandt, R. Wallauer, A. Kalinin, L. Ph. H. Schmidt, M. S. Schöffler, Y.-C. Chiang, T. Jahnke, and R. Dörner |