260 research outputs found
Single-qubit optical quantum fingerprinting
We analyze and demonstrate the feasibility and superiority of linear optical
single-qubit fingerprinting over its classical counterpart. For one-qubit
fingerprinting of two-bit messages, we prepare `tetrahedral' qubit states
experimentally and show that they meet the requirements for quantum
fingerprinting to exceed the classical capability. We prove that shared
entanglement permits 100% reliable quantum fingerprinting, which will
outperform classical fingerprinting even with arbitrary amounts of shared
randomness.Comment: 4 pages, one figur
On the relationship between pump chirp and single-photon chirp in spontaneous parametric downconversion
We study the chronocyclic character, i.e. the joint temporal and spectral
properties, of the single-photon constituents of photon pairs generated by
spontaneous parametric down conversion. In particular we study how single
photon properties, including purity and single-photon chirp, depend on photon
pair properties, including the type of signal-idler spectral and correlations
and the level of pump chirp.Comment: 13 pages, 6 figure
Subnanosecond spectral diffusion of a single quantum dot in a nanowire
We have studied spectral diffusion of the photoluminescence of a single CdSe
quantum dot inserted in a ZnSe nanowire. We have measured the characteristic
diffusion time as a function of pumping power and temperature using a recently
developed technique [G. Sallen et al, Nature Photon. \textbf{4}, 696 (2010)]
that offers subnanosecond resolution. These data are consistent with a model
where only a \emph{single} carrier wanders around in traps located in the
vicinity of the quantum dot
Mode-coupling theory for structural and conformational dynamics of polymer melts
A mode-coupling theory for dense polymeric systems is developed which
unifyingly incorporates the segmental cage effect relevant for structural
slowing down and polymer chain conformational degrees of freedom. An ideal
glass transition of polymer melts is predicted which becomes molecular-weight
independent for large molecules. The theory provides a microscopic
justification for the use of the Rouse theory in polymer melts, and the results
for Rouse-mode correlators and mean-squared displacements are in good agreement
with computer simulation results.Comment: 4 pages, 3 figures, Phys. Rev. Lett. in pres
Polymer-specific effects of bulk relaxation and stringlike correlated motion in the dynamics of a supercooled polymer melt
We analyze dynamical heterogeneities in a simulated “bead-spring” model of a nonentangled, supercooled polymer melt. We explore the importance of chain connectivity on the spatially heterogeneous motion of the monomers. We find that when monomers move, they tend to follow each other in one-dimensional paths, forming strings as previously reported in atomic liquids and colloidal suspensions. The mean string length is largest at a time close to the peak time of the mean cluster size of mobile monomers. This maximum string length increases, roughly in an exponential fashion, on cooling toward the critical temperature TMCTTMCT of the mode-coupling theory, but generally remains small, although large strings involving ten or more monomers are observed. An important contribution to this replacement comes from directly bonded neighbors in the chain. However, mobility is not concentrated along the backbone of the chains. Thus, a relaxation mechanism in which neighboring mobile monomers along the chain move predominantly along the backbone of the chains, seems unlikely for the system studied. © 2003 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/69784/2/JCPSA6-119-10-5290-1.pd
Publisher’s Note: “Polymer-specific effects of bulk relaxation and stringlike correlated motion in the dynamics of a supercooled polymer melt” [J. Chem. Phys. 119, 5290 (2003)]
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/70462/2/JCPSA6-120-14-6798-1.pd
Subnanosecond spectral diffusion measurement using photon correlation
Spectral diffusion is a result of random spectral jumps of a narrow line as a
result of a fluctuating environment. It is an important issue in spectroscopy,
because the observed spectral broadening prevents access to the intrinsic line
properties. However, its characteristic parameters provide local information on
the environment of a light emitter embedded in a solid matrix, or moving within
a fluid, leading to numerous applications in physics and biology. We present a
new experimental technique for measuring spectral diffusion based on photon
correlations within a spectral line. Autocorrelation on half of the line and
cross-correlation between the two halves give a quantitative value of the
spectral diffusion time, with a resolution only limited by the correlation
set-up. We have measured spectral diffusion of the photoluminescence of a
single light emitter with a time resolution of 90 ps, exceeding by four orders
of magnitude the best resolution reported to date
Efficient single-photon emission from electrically driven InP quantum dots epitaxially grown on Si(001)
The heteroepitaxy of III-V semiconductors on silicon is a promising approach
for making silicon a photonic platform for on-chip optical interconnects and
quantum optical applications. Monolithic integration of both material systems
is a long-time challenge, since different material properties lead to high
defect densities in the epitaxial layers. In recent years, nanostructures
however have shown to be suitable for successfully realising light emitters on
silicon, taking advantage of their geometry. Facet edges and sidewalls can
minimise or eliminate the formation of dislocations, and due to the reduced
contact area, nanostructures are little affected by dislocation networks. Here
we demonstrate the potential of indium phosphide quantum dots as efficient
light emitters on CMOS-compatible silicon substrates, with luminescence
characteristics comparable to mature devices realised on III-V substrates. For
the first time, electrically driven single-photon emission on silicon is
presented, meeting the wavelength range of silicon avalanche photo diodes'
highest detection efficiency
Diffusion and interface effects during preparation of all-solid microstructured fibers
All-solid microstructured optical fibers (MOF) allow the realization of very flexible optical waveguide designs. They are prepared by stacking of doped silica rods or canes in complex arrangements. Typical dopants in silica matrices are germanium and phosphorus to increase the refractive index (RI), or boron and fluorine to decrease the RI. However, the direct interface contact of stacking elements often causes interrelated chemical reactions or evaporation during thermal processing. The obtained fiber structures after the final drawing step thus tend to deviate from the targeted structure risking degrading their favored optical functionality. Dopant profiles and design parameters(e.g., the RI homogeneity of the cladding) are controlled by the combination of diffusion and equilibrium conditions of evaporation reactions. We show simulation results of diffusion and thermal dissociation in germanium and fluorine doped silica rod arrangements according to the monitored geometrical disturbances in stretched canes or drawn fibers. The paper indicates geometrical limits of dopant structures in sub-ÎĽm-level depending on the dopant concentration and the thermal conditions during the drawing process. The presented results thus enable an optimized planning of the preform parameters avoiding unwanted alterations in dopant concentration profiles or in design parameters encountered during the drawing process
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