664 research outputs found
Occurrence of Two Species of Old World Bees, \u3ci\u3eAnthidium Manicatum\u3c/i\u3e and \u3ci\u3eA. Oblongatum\u3c/i\u3e (Apoidea: Megachilidae), in Northern Ohio and Southern Michigan
Anthidium manicatum and A. oblongatum are two European bees species that have recently established themselves in North America. Anthidium manicatum has previously been documented in New York and Ontario, Canada, and A. oblongatum has been documented in New York, New Jersey, Maryland, and eastern Pennsylvania. We surveyed a number of sites in Ohio, Michigan, and Indiana for these species in 2000 and 2001, and found both bee species to have extended their ranges into northern Ohio, and A. manicatum to have moved into southern Michigan. We present a key identifying the four Anthidium species now known from northeastern North America
Switched Control of Electron Nuclear Spin Systems
In this article, we study control of electron-nuclear spin dynamics at
magnetic field strengths where the Larmor frequency of the nucleus is
comparable to the hyperfine coupling strength. The quantization axis for the
nuclear spin differs from the static B_0 field direction and depends on the
state of the electron spin. The quantization axis can be switched by flipping
the state of electron spin, allowing for universal control on nuclear spin
states. We show that by performing a sequence of flips (each followed by a
suitable delay), we can perform any desired rotation on the nuclear spins,
which can also be conditioned on the state of the electron spin. These
operations, combined with electron spin rotations can be used to synthesize any
unitary transformation on the coupled electron-nuclear spin system. We discuss
how these methods can be used for design of experiments for transfer of
polarization from the electron to the nuclear spins
A model for liquid phase sintering
AbstractA quantitative model for liquid phase sintering is developed based on the following ideas. During heating a liquid phase forms, which is easily mobile, wets the solid particles completely, dissolves solid atoms and provides an easy diffusion path for them. The solid density increases by particle rearrangement and by the flattening of particle contacts. Driving (or retarding) forces result from capillary stresses, from applied mechanical stresses, from the pressure of gas entrapped in closed pores and from differences in chemical potential of the dissolved and precipitated matter. At higher densities the driving force may become very small, since the liquid pressure decreases and a negative contribution from the solid-liquid interface energy increases. At this stage grain coarsening plays an important role for the continued filling of larger and larger pores. The model is applied to describe nonisothermal densification curves measured on Si3N4 for various hold temperatures, axial stresses and green densities. Adjusting a moderate number of parameters all having a physical meaning leads to good agreement between theory and experiment
Spin-flip and spin-conserving optical transitions of the nitrogen-vacancy centre in diamond
We map out the first excited state sublevel structure of single nitrogen-vacancy (NV) colour centres in diamond. The excited state is an orbital doublet where one branch supports an efficient cycling transition, while the other can simultaneously support fully allowed optical Raman spin-flip transitions. This is crucial for the success of many recently proposed quantum information applications of the NV defects. We further find that an external electric field can be used to completely control the optical properties of a single centre. Finally, a group theoretical model is developed that explains the observations and provides good physical understanding of the excited state structure
Coherence properties of a single dipole emitter in diamond
On-demand, high repetition rate sources of indistinguishable, polarised
single photons are the key component for future photonic quantum technologies.
Colour centres in diamond offer a promising solution, and the narrow line-width
of the recently identified nickel-based NE8 centre makes it particularly
appealing for realising the transform-limited sources necessary for quantum
interference. Here we report the characterisation of dipole orientation and
coherence properties of a single NE8 colour centre in a diamond nanocrystal at
room-temperature. We observe a single photon coherence time of 0.21 ps and an
emission lifetime of 1.5 ns. Combined with an emission wavelength that is
ideally suited for applications in existing quantum optical systems, these
results show that the NE8 is a far more promising source than the more commonly
studied nitrogen-vacancy centre and point the way to the realisation of a
practical diamond colour centre-based single photon source.Comment: 10 pages, 4 colour figure
Room temperature triggered single-photon source in the near infrared
We report the realization of a solid-state triggered single-photon source
with narrow emission in the near infrared at room temperature. It is based on
the photoluminescence of a single nickel-nitrogen NE8 colour centre in a
chemical vapour deposited diamond nanocrystal. Stable single-photon emission
has been observed in the photoluminescence under both continuous-wave and
pulsed excitations. The realization of this source represents a step forward in
the application of diamond-based single-photon sources to Quantum Key
Distribution (QKD) under practical operating conditions.Comment: 10 page
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