434 research outputs found
Optimizing single-photon-source heralding efficiency at 1550 nm using periodically poled lithium niobate
We explore the feasibility of using high conversion-efficiency
periodically-poled crystals to produce photon pairs for photon-counting
detector calibrations at 1550 nm. The goal is the development of an appropriate
parametric down-conversion (PDC) source at telecom wavelengths meeting the
requirements of high-efficiency pair production and collection in single
spectral and spatial modes (single-mode fibers). We propose a protocol to
optimize the photon collection, noise levels and the uncertainty evaluation.
This study ties together the results of our efforts to model the single-mode
heralding efficiency of a two-photon PDC source and to estimate the heralding
uncertainty of such a source.Comment: 14 pages, 2 tables and 3 figures, final version accepted by
Metrologi
Single Photon Source with Individualized Single Photon Certifications
As currently implemented, single-photon sources cannot be made to produce
single photons with high probability, while simultaneously suppressing the
probability of yielding two or more photons. Because of this, single photon
sources cannot really produce single photons on demand. We describe a
multiplexed system that allows the probabilities of producing one and more
photons to be adjusted independently, enabling a much better approximation of a
source of single photons on demand. The scheme uses a heralded photon source
based on parametric downconversion, but by effectively breaking the trigger
detector area into multiple regions, we are able to extract more information
about a heralded photon than is possible with a conventional arrangement. This
scheme allows photons to be produced along with a quantitative
``certification'' that they are single photons. Some of the single-photon
certifications can be significantly better than what is possible with
conventional downconversion sources (using a unified trigger detector region),
as well as being better than faint laser sources. With such a source of more
tightly certified single photons, it should be possible to improve the maximum
secure bit rate possible over a quantum cryptographic link. We present an
analysis of the relative merits of this method over the conventional
arrangement.Comment: 11 pages, 5 figures, SPIE Free-Space Laser Communication and Laser
Imaging II. To appear in the proceeding of SPIE Free-Space Laser
Communication and Laser Imaging II, vol 482
Imaging and quantum efficiency measurement of chromium emitters in diamond
We present direct imaging of the emission pattern of individual
chromium-based single photon emitters in diamond and measure their quantum
efficiency. By imaging the excited state transition dipole intensity
distribution in the back focal plane of high numerical aperture objective, we
determined that the emission dipole is oriented nearly orthogonal to the
diamond-air interface. Employing ion implantation techniques, the emitters were
engineered with various proximities from the diamond-air interface. By
comparing the decay rates from the single chromium emitters at different depths
in the diamond crystal, an average quantum efficiency of 28% was measured.Comment: 11 pages and 4 figure
Hyperbolic Metamaterial Resonator-Antenna Scheme for Large, Broadband Emission Enhancement and Single Photon Collection
We model the broadband enhancement of single-photon emission from color
centres in silicon carbide nanocrystals coupled to a planar hyperbolic
metamaterial, HMM resonator. The design is based on positioning the single
photon emitters within the HMM resonator, made of a dielectric index-matched
with silicon-carbide material. The broadband response results from the
successive resonance peaks of the lossy Fabry Perot structure modes arising
within the high-index HMM cavity. To capture this broadband enhancement in the
single photon emitters spontaneous emission, we placed a simple gold based
cylindrical antenna on top of the HMM resonator. We analyzed the performance of
this HMM coupled antenna structure in terms of the Purcell enhancement, quantum
efficiency, collection efficiency and overall collected photon rate. For
perpendicular dipole orientation relative to the interface, the HMM coupled
antenna resonator leads to a significantly large spontaneous emission
enhancement with Purcell factor of the order of 250 along with a very high
average total collected photon rate, CPR of about 30 over a broad emission
spectrum, 700 nm to 1000 nm. The peak CPR increases to about 80 at 900 nm,
corresponding to the emission of silicon-carbide quantum emitters. This is a
state of the art improvement considering the previous computational designs
have reported a maximum average CPR of 25 across the nitrogen-vacancy centre
emission spectrum, 600 nm to 800 nm with the highest value being about 40 at
650 nm
Heralded single photon sources: a route towards quantum communication technology and photon standards
Single photon counting, based on single photon sources and detectors, is a key ingredient for certain applications aiming at new quantum information technologies. Quantum cryptography, quantum radiometry, distributed quantum computing, as well as adjacent technologies such as biomedical and astronomical imaging, and low power classical communication also rely on single-photon technology. This paper reviews the present status of single photon sources and related counting measurement techniques, based on correlated (or heralded) photons in parametric down-conversion, and their possible impact on the above mentioned technologies, as well as an assessment for photon standards in the future
Radiative and nonradiative decay rates in chromium-related centers in nanodiamonds
We address for the first time the measurement of nonradiative decay rates in Cr-related centers in nanodiamonds. Compared to our previous quantum efficiency measurement of Cr centers created in bulk diamond, separate measurements of radiative and nonradiative decay rates in grown nanodiamonds prove more challenging due to size dependence effects. We demonstrate in this Letter that, using defocused dipole imaging and collection efficiency calculation via finite-difference time-domain (FDTD), a quantum efficiency up to 0.9 can be inferred to Cr-related centers showing a 2-level system photon statistic
Nonlinear multigrid based on local spectral coarsening for heterogeneous diffusion problems
This work develops a nonlinear multigrid method for diffusion problems
discretized by cell-centered finite volume methods on general unstructured
grids. The multigrid hierarchy is constructed algebraically using aggregation
of degrees of freedom and spectral decomposition of reference linear operators
associated with the aggregates. For rapid convergence, it is important that the
resulting coarse spaces have good approximation properties. In our approach,
the approximation quality can be directly improved by including more spectral
degrees of freedom in the coarsening process. Further, by exploiting local
coarsening and a piecewise-constant approximation when evaluating the nonlinear
component, the coarse level problems are assembled and solved without ever
re-visiting the fine level, an essential element for multigrid algorithms to
achieve optimal scalability. Numerical examples comparing relative performance
of the proposed nonlinear multigrid solvers with standard single-level
approaches -- Picard's and Newton's methods -- are presented. Results show that
the proposed solver consistently outperforms the single-level methods, both in
efficiency and robustness
The U.S. Integrated Ocean Observing System (IOOS): A Prototype User Valuation
The Integrated Ocean Observing System of the United States provides a large variety of oceanographic and related data at no charge through 11 Regional Associations. Since the data is distributed without price it is difficult to determine the economic value of the data. That value is useful in explaining and justifying the investment in ocean observing. This study applies discrete choice modeling to determine valuation of the data for users of data through the RA websites. The study found annual values of 220 million, and these estimates are considered highly conservative. A guide for replication of the valuation study is included
Quantum and Classical Noise in Practical Quantum Cryptography Systems based on polarization-entangled photons
Quantum-cryptography key distribution (QCKD) experiments have been recently
reported using polarization-entangled photons. However, in any practical
realization, quantum systems suffer from either unwanted or induced
interactions with the environment and the quantum measurement system, showing
up as quantum and, ultimately, statistical noise. In this paper, we investigate
how ideal polarization entanglement in spontaneous parametric downconversion
(SPDC) suffers quantum noise in its practical implementation as a secure
quantum system, yielding errors in the transmitted bit sequence. Because all
SPDC-based QCKD schemes rely on the measurement of coincidence to assert the
bit transmission between the two parties, we bundle up the overall quantum and
statistical noise in an exhaustive model to calculate the accidental
coincidences. This model predicts the quantum-bit error rate and the sifted key
and allows comparisons between different security criteria of the hitherto
proposed QCKD protocols, resulting in an objective assessment of performances
and advantages of different systems.Comment: Rev Tex Style, 2 columns, 7 figures, (a modified version will appear
on PRA
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