Controlling the emission from single quantum dots with electro-opto- mechanical photonic crystal cavities

We present a device for the spectral reconfiguration of a two-dimensional photonic crystal cavity (PCC) based on parallel semiconductor membranes. The mechanical motion of the slabs introduces a variation in the effective refractive index of the coupled waveguides where the photonic crystal is etched resulting in a shift of the free-space wavelength. Using an integrated electrostatic actuator we demonstrated independent tuning up to 15 nm with less than 6 V bias. We present the electromechanical control of a PCC mode in resonance to single quantum dot (QD) emission lines for the real-time compensation of the spectral mismatch due to the dots\u27 inhomogeneity. We discuss the operation of the device at low temperatures (\u3c 10 K) and we measured the Purcell effect via the electro-mechanical control. A reversible tuning range of 13 nm and a spontaneous emission rate control by a factor of ten has been achieved. © 2013 IEEE

Funneling single photons into ridge-waveguide photonic integrated circuits

The generation, manipulation and detection of single photons enable quantum communication, simulation and potentially computing protocols. However scaling to several qubits requires the integration of these functionalities in a single chip. A promising approach to the integration of single-photon sources in a chip is the use of single quantum dots embedded in photonic crystal waveguides or cavities. To this aim, efficient coupling of the emission from single quantum dots in photonic crystal cavities to low-loss ridge-waveguide (RWG) circuits is needed. This is usually hampered by the large mode mismatch between the two systems. In this work the emission of a photonic crystal (PhC) cavity realized on a GaAs/AlGaAs membrane and pumped by quantum dots has been effectively coupled and transferred through a long RWG (∼1mm). By continuous tapering in both horizontal and vertical direction, transmission values (fiber-in, fiber-out) around 0.16 and 0.08% for RWG and coupled PhC waveguide-RWG have been achieved, respectively. This corresponds to about 2.8% coupling efficiency between the center of the PhC waveguide and the single-mode output fiber, a value much higher than what is achieved by top collection. It further shows that around 70% of the light in the PhC waveguide is coupled to the RWG. The emission from quantum dots in the cavity has been clearly identified by exciting from the top and collecting the photoluminescence from the cleaved facet of the device 1mm away from the cavity which enables the efficient coupling of single photons to RWG and detector circuits. © 2013 SPIE

Lipolytic enzymes and hydrolytic rancidity

Lipolysis, the enzymic hydrolysis of milk lipids to free fatty acids and partial glycerides, is a constant concern to the dairy industry because of the detrimental effcts it can have on the flvor and other properties of milk and milk products. However, free fatty acids also contribute to the desirable flavor of milk and milk products when present at low concentrations and, in some cheeses, when present at high concentrations. The enzymes responsible for the detrimental effects of lipolysis are of two main types: those indigenous to milk, and those of microbial origin. The major indigenous milk enzyme is lipoprotein lipase. It is active on the fat in natural milk fat globules only after their disruption by physical treatments or if certain blood serum lipoproteins are present. The major microbial lipases are produced by psychrotrophic bacteria. Many of these enzymes are heat stable and are particularly significant in stored products. Human milk differs from cows' milk in that it contains two lipases, a lipoprotein lipase and a bile salt-stimulated lipase. The ability of the latter to cause considerable hydrolysis of ingested milk lipids has important nutritional implications