Waveguide coupling of single photons from a solid state emitter

Mr Samuele Grandi
Faculty of Natural Sciences, Department of Physics, Imperial College London
4pm Thursday 15 September 2016
CQC2T Conference Room Level 2, Newton Building, UNSW

The organic dye molecule dibenzoterrylene (DBT) in an anthracene crystal matrix is a promising
candidate for single photon emission. At cryogenic temperatures, this system presents a narrow
lifetime-limited transition at 785nm, with a quantum yield close to unity. Moreover, DBT
molecules have been shown to act as a mediator for photon-photon interactions, by inducing a
phase-shift on a passing photon when another photon is present. These features make DBT
molecules a powerful tool for quantum information purposes, including use as single photon sources
and controlled quantum gates. For these to be achieved, the interaction between the molecule and
the radiation field must be enhanced.
We plan to accomplish this task by integrating single molecules in nano-photonic structures. We have
designed and fabricated single mode ridge waveguides, optimised to have maximum overlap between
their evanescent field and the molecule. To further enhance the interaction, we have inserted a nanotrench
in a waveguide, further increasing the coupling to the structure. Simulations shown an
expected 52% of the light radiated from to the molecule to be harnessed in the waveguide. A growth
method developed in our group allows deposition of a thin film of anthracene doped with DBT on
top of the structures. To move beyond the diffraction limit, we have designed a plasmonic hybrid
waveguide. These waveguides provide an adiabatic transition to the plasmonic regime, while
minimising the losses typically associated with interactions between light and metals.
Since most quantum information protocols require direct manipulation of the state of the molecule,
we have studied its coherent dynamics in the presence of dephasing. By solving analytically the
optical Bloch equation, we are now able to model the response of any two-level system, a result we
have validated experimentally with our molecules.