562 research outputs found
Current noise of a quantum dot p-i-n junction in a photonic crystal
The shot-noise spectrum of a quantum dot p-i-n junction embedded inside a
three-dimensional photonic crystal is investigated. Radiative decay properties
of quantum dot excitons can be obtained from the observation of the current
noise. The characteristic of the photonic band gap is revealed in the current
noise with discontinuous behavior. Applications of such a device in
entanglement generation and emission of single photons are pointed out, and may
be achieved with current technologies.Comment: 4 pages, 3 figures, to appear in Phys. Rev. B (2005
Size dependent line broadening in the emission spectra of single GaAs quantum dots: Impact of surface charges on spectral diffusion
Making use of droplet epitaxy, we systematically controlled the height of
self-assembled GaAs quantum dots by more than one order of magnitude. The
photoluminescence spectra of single quantum dots revealed the strong dependence
of the spectral linewidth on the dot height. Tall dots with a height of ~30 nm
showed broad spectral peaks with an average width as large as ~5 meV, but
shallow dots with a height of ~2 nm showed resolution-limited spectral lines
(<120 micro eV). The measured height dependence of the linewidths is in good
agreement with Stark coefficients calculated for the experimental shape
variation. We attribute the microscopic source of fluctuating electric fields
to the random motion of surface charges at the vacuum-semiconductor interface.
Our results offer guidelines for creating frequency-locked photon sources,
which will serve as key devices for long-distance quantum key distribution.Comment: 6 pages, 6 figures; updated figs and their description
Symmetry characterization of eigenstates in opal-based photonic crystals
The complete symmetry characterization of eigenstates in bare opal systems is
obtained by means of group theory. This symmetry assignment has allowed us to
identify several bands that cannot couple with an incident external plane wave.
Our prediction is supported by layer-KKR calculations, which are also
performed: the coupling coefficients between bulk modes and externally excited
field tend to zero when symmetry properties mismatch.Comment: 7 pages, 5 figures, submitted to Physical Review
Bunching visibility for correlated photons from single GaAs quantum dots
We study photon bunching phenomena associated with biexciton-exciton cascade
in single GaAs self-assembled quantum dots. Experiments carried out with a
pulsed excitation source show that significant bunching is only detectable at
very low excitation, where the typical intensity of photon streams is less than
the half of their saturation value. Our findings are qualitatively understood
with a model which accounts for Poissonian statistics in the number of
excitons, predicting the height of a bunching peak being determined by the
inverse of probability of finding more than one exciton.Comment: 6 pages, 6 figs to appear in Phys. Rev.
Quantitative characterization of the Antarctic ozone hole
The long-term evolution of the Antarctic ozone hole is studied based on the TOMS data and the JMA data-set of stratospheric temperature in relation with the possible role of polar stratospheric clouds (PSC's). The effective mass of depleted ozone in the ozone hole at its annual mature stage reached a historical maximum of 55 Mt in 1991, 4.3 times larger than in 1981. The ozone depletion rate during 30 days before the mature ozone hole does not show any appreciable long-term trend but the interannual fluctuations do, ranging from 0.169 to 0.689 Mt/day with the average of 0.419 Mt/day for the period of 1979 - 1991. The depleted ozone mass has the highest correlation with the region below 195 K on the 30 mb surface in June, whereas the ozone depletion rate correlates most strongly with that in August. The present result strongly suggests that the long-term evolution of the mature ozone hole is caused both by the interannual change of the latitudinal coverage of the early PSC's, which may control the latitude and date of initiation of ozone decrease, and by that of the spatial coverage of the mature PSC's which may control the ozone depletion rate in the Antarctic spring
Vertical beaming of wavelength-scale photonic crystal resonators
We report that of the photons generated inside a photonic crystal
slab resonator can be funneled within a small divergence angle of . The far-field radiation properties of a photonic crystal slab
resonant mode are modified by tuning the cavity geometry and by placing a
reflector below the cavity. The former method directly shapes the near-field
distribution so as to achieve directional and linearly-polarized far-field
patterns. The latter modification takes advantage of the interference effect
between the original waves and the reflected waves to enhance the
energy-directionality. We find that, regardless of the slab thickness, the
optimum distance between the slab and the reflector closely equals one
wavelength of the resonance under consideration. We have also discussed an
efficient far-field simulation algorithm based on the finite-difference
time-domain method and the near- to far-field transformation.Comment: 14 pages, 15 figures, submitted to Phys. Rev.
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