219 research outputs found
Practical decoy state method in quantum key distribution with heralded single photon source
We propose a practical decoy state method with heralded single photon source
for quantum key distribution (QKD). In the protocol, 3 intensities are used and
one can estimate the fraction of single-photon counts. The final key rate over
transmission distance is simulated under various parameter sets. Due to the
lower dark count than that of a coherent state, it is shown that a 3-intensity
decoy-state QKD with a heralded source can work for a longer distance than that
of a coherent state.Comment: 10 pages, 4 Postscript figure
Long-distance entanglement-based quantum key distribution over optical fiber
We report the first entanglement-based quantum key distribution (QKD) experiment over a 100-km optical fiber. We used superconducting single photon detectors based on NbN nanowires that provide high-speed single photon detection for the 1.5-µm telecom band, an efficient entangled photon pair source that consists of a fiber coupled periodically poled lithium niobate waveguide and ultra low loss filters, and planar lightwave circuit Mach-Zehnder interferometers (MZIs) with ultra stable operation. These characteristics enabled us to perform an entanglement-based QKD experiment over a 100-km optical fiber. In the experiment, which lasted approximately 8 hours, we successfully generated a 16 kbit sifted key with a quantum bit error rate of 6.9 % at a rate of 0.59 bits per second, from which we were able to distill a 3.9 kbit secure key
Supramolecular interactions in clusters of polar and polarizable molecules
We present a model for molecular materials made up of polar and polarizable
molecular units. A simple two state model is adopted for each molecular site
and only classical intermolecular interactions are accounted for, neglecting
any intermolecular overlap. The complex and interesting physics driven by
interactions among polar and polarizable molecules becomes fairly transparent
in the adopted model. Collective effects are recognized in the large variation
of the molecular polarity with supramolecular interactions, and cooperative
behavior shows up with the appearance, in attractive lattices, of discontinuous
charge crossovers. The mean-field approximation proves fairly accurate in the
description of the gs properties of MM, including static linear and non-linear
optical susceptibilities, apart from the region in the close proximity of the
discontinuous charge crossover. Sizeable deviations from the excitonic
description are recognized both in the excitation spectrum and in linear and
non-linear optical responses. New and interesting phenomena are recognized near
the discontinuous charge crossover for non-centrosymmetric clusters, where the
primary photoexcitation event corresponds to a multielectron transfer.Comment: 14 pages, including 11 figure
Quantum Transduction of Telecommunications-band Single Photons from a Quantum Dot by Frequency Upconversion
The ability to transduce non-classical states of light from one wavelength to
another is a requirement for integrating disparate quantum systems that take
advantage of telecommunications-band photons for optical fiber transmission of
quantum information and near-visible, stationary systems for manipulation and
storage. In addition, transducing a single-photon source at 1.3 {\mu}m to
visible wavelengths for detection would be integral to linear optical quantum
computation due to the challenges of detection in the near-infrared. Recently,
transduction at single-photon power levels has been accomplished through
frequency upconversion, but it has yet to be demonstrated for a true
single-photon source. Here, we transduce the triggered single-photon emission
of a semiconductor quantum dot at 1.3 {\mu}m to 710 nm with a total detection
(internal conversion) efficiency of 21% (75%). We demonstrate that the 710 nm
signal maintains the quantum character of the 1.3 {\mu}m signal, yielding a
photon anti-bunched second-order intensity correlation, g^(2)(t), that shows
the optical field is composed of single photons with g^(2)(0) = 0.165 < 0.5.Comment: 7 pages, 4 figure
A photonic quantum information interface
Quantum communication is the art of transferring quantum states, or quantum
bits of information (qubits), from one place to another. On the fundamental
side, this allows one to distribute entanglement and demonstrate quantum
nonlocality over significant distances. On the more applied side, quantum
cryptography offers, for the first time in human history, a provably secure way
to establish a confidential key between distant partners. Photons represent the
natural flying qubit carriers for quantum communication, and the presence of
telecom optical fibres makes the wavelengths of 1310 and 1550 nm particulary
suitable for distribution over long distances. However, to store and process
quantum information, qubits could be encoded into alkaline atoms that absorb
and emit at around 800 nm wavelength. Hence, future quantum information
networks made of telecom channels and alkaline memories will demand interfaces
able to achieve qubit transfers between these useful wavelengths while
preserving quantum coherence and entanglement. Here we report on a qubit
transfer between photons at 1310 and 710 nm via a nonlinear up-conversion
process with a success probability greater than 5%. In the event of a
successful qubit transfer, we observe strong two-photon interference between
the 710 nm photon and a third photon at 1550 nm, initially entangled with the
1310 nm photon, although they never directly interacted. The corresponding
fidelity is higher than 98%.Comment: 7 pages, 3 figure
Temporal mode selectivity by frequency conversion in second-order nonlinear optical waveguides
We explore theoretically the feasibility of using frequency conversion by
sum- or difference-frequency generation, enabled by three- wave-mixing, for
selectively multiplexing orthogonal input waveforms that overlap in time and
frequency. Such a process would enable a drop device for use in a transparent
optical network using temporally orthogonal waveforms to encode different
channels. We model the process using coupled-mode equations appropriate for
wave mixing in a uniform second- order nonlinear optical medium pumped by a
strong laser pulse. We find Green functions describing the process, and employ
Schmidt (singular- value) decompositions thereof to quantify its viability in
functioning as a coherent waveform discriminator. We define a selectivity
figure of merit in terms of the Schmidt coefficients, and use it to compare and
contrast various parameter regimes via extensive numerical computations. We
identify the most favorable regime (at least in the case of no pump chirp) and
derive the complete analytical solution for the same. We bound the maximum
achievable selectivity in this parameter space. We show that including a
frequency chirp in the pump does not improve selectivity in this optimal
regime. We also find an operating regime in which high-efficiency frequency
conversion without temporal-shape selectivity can be achieved while preserving
the shapes of a wide class of input pulses. The results are applicable to both
classical and quantum frequency conversion.Comment: 24 pages, 20 figure
Україна – Канада: сучасні наукові студії
The materials of the international collective monograph show the latest Ukrainian-Canadian socio-political, historical, philological, cultural, educational and pedagogical research in the field of modern Canadian Studies. The monograph includes the investigations by several scientists from Ukraine and Canada (from Edmonton, Lutsk, Kyiv, Lviv, and Sumy). Such publication comes out in Ukraine for the first time. For scholars, postgraduates and doctoral students, undergraduates and lecturers of the faculties of international relations, foreign philology, history, political science, philology and journalism, education and social work, Canadian centres in Ukraine and centres of Ukrainian Studies in Canada, as well as for anyone interested in research of Ukrainian-Canadian relations
Specific In Vivo Staining of Astrocytes in the Whole Brain after Intravenous Injection of Sulforhodamine Dyes
Fluorescent staining of astrocytes without damaging or interfering with normal brain functions is essential for intravital microscopy studies. Current methods involved either transgenic mice or local intracerebral injection of sulforhodamine 101. Transgenic rat models rarely exist, and in mice, a backcross with GFAP transgenic mice may be difficult. Local injections of fluorescent dyes are invasive. Here, we propose a non-invasive, specific and ubiquitous method to stain astrocytes in vivo. This method is based on iv injection of sulforhodamine dyes and is applicable on rats and mice from postnatal age to adulthood. The astrocytes staining obtained after iv injection was maintained for nearly half a day and showed no adverse reaction on astrocytic calcium signals or electroencephalographic recordings in vivo. The high contrast of the staining facilitates the image processing and allows to quantify 3D morphological parameters of the astrocytes and to characterize their network. Our method may become a reference for in vivo staining of the whole astrocytes population in animal models of neurological disorders
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