22 research outputs found

    Excited states of a static dilute spherical Bose condensate in a trap

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    The Bogoliubov approximation is used to study the excited states of a dilute gas of NN atomic bosons trapped in an isotropic harmonic potential characterized by a frequency ω0\omega_0 and an oscillator length d0=/mω0d_0 = \sqrt{\hbar/m\omega_0}. The self-consistent static Bose condensate has macroscopic occupation number N01N_0 \gg 1, with nonuniform spherical condensate density n0(r)n_0(r); by assumption, the depletion of the condensate is small (NNN0N0N' \equiv N - N_0\ll N_0). The linearized density fluctuation operator ρ^\hat \rho' and velocity potential operator Φ^\hat\Phi' satisfy coupled equations that embody particle conservation and Bernoulli's theorem. For each angular momentum ll, introduction of quasiparticle operators yields coupled eigenvalue equations for the excited states; they can be expressed either in terms of Bogoliubov coherence amplitudes ul(r)u_l(r) and vl(r)v_l(r) that determine the appropriate linear combinations of particle operators, or in terms of hydrodynamic amplitudes ρl(r)\rho_l'(r) and Φl(r)\Phi_l'(r). The hydrodynamic picture suggests a simple variational approximation for l>0l >0 that provides an upper bound for the lowest eigenvalue ωl\omega_l and an estimate for the corresponding zero-temperature occupation number NlN_l'; both expressions closely resemble those for a uniform bulk Bose condensate.Comment: 5 pages, RevTeX, contributed paper accepted for Low Temperature Conference, LT21, August, 199

    Low-temperature tapered-fiber probing of diamond NV ensembles coupled to GaP microcavities

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    In this work we present a platform for testing the device performance of a cavity-emitter system, using an ensemble of emitters and a tapered optical fiber. This method provides high-contrast spectra of the cavity modes, selective detection of emitters coupled to the cavity, and an estimate of the device performance in the single- emitter case. Using nitrogen-vacancy (NV) centers in diamond and a GaP optical microcavity, we are able to tune the cavity onto the NV resonance at 10 K, couple the cavity-coupled emission to a tapered fiber, and measure the fiber-coupled NV spontaneous emission decay. Theoretically we show that the fiber-coupled average Purcell factor is 2-3 times greater than that of free-space collection; although due to ensemble averaging it is still a factor of 3 less than the Purcell factor of a single, ideally placed center.Comment: 15 pages, 6 figure

    Hybrid photonic crystal cavity and waveguide for coupling to diamond NV-centers

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    A design for an ultra-high Q photonic crystal nanocavity engineered to interact with nitrogen-vacancy (NV) centers located near the surface of a single crystal diamond sample is presented. The structure is based upon a nanowire photonic crystal geometry, and consists of a patterned high refractive index membrane, such as gallium phosphide (GaP), supported by a diamond substrate. The nanocavity supports a mode with quality factor Q > 1.5 million and mode volume V < 0.52 (\lambda/n_\text{GaP})^3, and promises to allow Purcell enhanced collection of spontaneous emission from an NV located more than 50 nm below the diamond surface. The nanowire photonic crystal waveguide can be used to efficiently couple light into and out of the cavity, or as an efficient broadband collector of NV phonon sideband emission. The proposed structures can be fabricated using existing materials and processing techniques

    One- and two-dimensional photonic crystal micro-cavities in single crystal diamond

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    The development of solid-state photonic quantum technologies is of great interest for fundamental studies of light-matter interactions and quantum information science. Diamond has turned out to be an attractive material for integrated quantum information processing due to the extraordinary properties of its colour centres enabling e.g. bright single photon emission and spin quantum bits. To control emitted photons and to interconnect distant quantum bits, micro-cavities directly fabricated in the diamond material are desired. However, the production of photonic devices in high-quality diamond has been a challenge so far. Here we present a method to fabricate one- and two-dimensional photonic crystal micro-cavities in single-crystal diamond, yielding quality factors up to 700. Using a post-processing etching technique, we tune the cavity modes into resonance with the zero phonon line of an ensemble of silicon-vacancy centres and measure an intensity enhancement by a factor of 2.8. The controlled coupling to small mode volume photonic crystal cavities paves the way to larger scale photonic quantum devices based on single-crystal diamond

    An Organism-Centered Approach to Some Community and Ecosystem Concepts

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    We present a discussion of the ecological concept of the niche based on the perspective of the individual organism, rather than that of a population or species. This discussion is then expanded to include other related ecological concepts such as guild, environment, habitat and functional group. Using the individual as the focus permits the development of a system of concepts which, we believe, approximate the way that ecological interactions occur in nature