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Physics Seminar

Organic molecules as sources of single photons

Speaker: Dr Alex S. Clark (Imperial College London)
Date: Wednesday 6 February 2019
Time: 15:00
Venue: Queens Buildings N/3.28

Photons lie at the heart of many quantum technologies. They are the only logical choice for sending quantum information over long distances, they have been used for many demonstrations of quantum simulations, they are often employed in microscopy to perform high-resolution imaging and they are promising candidates for quantum computing and networking. Still, they are difficult to generate and collect with high efficiency. In this talk I will discuss the use of organic molecules for generating single photons. When dibenzoterrylene (DBT) is embedded in anthracene it is photostable and forms a two-level system which when excited will emit a photon at a wavelength of ~780 nm. This is desirable as a number of atomic quantum technologies based on rubidium interact efficiently with light at this wavelength. Room temperature fluorescence from DBT can be used for communication, sensing, or to test the coupling of molecules to photonic devices, however I will show that it is difficult to efficiently and fully populate the excited state of a molecule in these conditions. I will show that by cooling to 77 K, the temperature of liquid nitrogen, we achieve almost 100% population inversion in DBT, and therefore efficiently generate photons. Further cooling is required to generate coherent, lifetime-limited photons. I will show our work in characterising a single molecule at temperatures down to 4 K and show that coherent Rabi oscillations are then seen in the excited state population. Clearly photons can be efficiently generated using DBT, but the next challenge is to collect those photons. I will discuss our recent work to couple the emission from single molecules into optical fibres using a microcavity and into photonic and plasmonic waveguides using nano-fabricated devices.