1,240 research outputs found
Quantum Cryptography using entangled photons in energy-time Bell states
We present a setup for quantum cryptography based on photon pairs in
energy-time Bell states and show its feasability in a laboratory experiment.
Our scheme combines the advantages of using photon pairs instead of faint laser
pulses and the possibility to preserve energy-time entanglement over long
distances. Moreover, using 4-dimensional energy-time states, no fast random
change of bases is required in our setup : Nature itself decides whether to
measure in the energy or in the time base.Comment: 4 pages including 2 figure
Pulsed energy-time entangled twin-photon source for quantum communication
A pulsed source of energy-time entangled photon pairs pumped by a standard
laser diode is proposed and demonstrated. The basic states can be distinguished
by their time of arrival. This greatly simplifies the realization of 2-photon
quantum cryptography, Bell state analyzers, quantum teleportation, dense
coding, entanglement swapping, GHZ-states sources, etc. Moreover the
entanglement is well protected during photon propagation in telecom optical
fibers, opening the door to few-photon applications of quantum communication
over long distances.Comment: 8 pages, 4 figure
Non-domestic phosphorus release in rivers during low-flow: Mechanisms and implications for sources identification
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
PPLN Waveguide for Quantum Communication
We report on energy-time and time-bin entangled photon-pair sources based on
a periodically poled lithium niobate (PPLN) waveguide. Degenerate twin photons
at 1314 nm wavelength are created by spontaneous parametric down-conversion and
coupled into standard telecom fibers. Our PPLN waveguide features a very high
conversion efficiency of about 10^(-6), roughly 4 orders of magnitude more than
that obtained employing bulk crystals. Even if using low power laser diodes,
this engenders a significant probability for creating two pairs at a time - an
important advantage for some quantum communication protocols. We point out a
simple means to characterize the pair creation probability in case of a pulsed
pump. To investigate the quality of the entangled states, we perform
photon-pair interference experiments, leading to visibilities of 97% for the
case of energy-time entanglement and of 84% for the case of time-bin
entanglement. Although the last figure must still be improved, these tests
demonstrate the high potential of PPLN waveguide based sources to become a key
element for future quantum communication schemesComment: 11 pages, 9 figures, submitted to the European Physical Journal D
(special issue of the Quick conference
New high-efficiency source of photon pairs for engineering quantum entanglement
We have constructed an efficient source of photon pairs using a
waveguide-type nonlinear device and performed a two-photon interference
experiment with an unbalanced Michelson interferometer. Parametric
down-converted photons from the nonlinear device are detected by two detectors
located at the output ports of the interferometer. Because the interferometer
is constructed with two optical paths of different length, photons from the
shorter path arrive at the detector earlier than those from the longer path. We
find that the difference of arrival time and the time window of the coincidence
counter are important parameters which determine the boundary between the
classical and quantum regime. When the time window of the coincidence counter
is smaller than the arrival time difference, fringes of high visibility
(80 10%) were observed. This result is only explained by quantum theory
and is clear evidence for quantum entanglement of the interferometer's optical
paths.Comment: 4 pages, 4 figures, IQEC200
Обеспечение безопасности при обращении с ядерными материалами на заводе по изготовлению твэл
Объектом исследования являются вопросы организации и функционирования систем физической защиты. Цель работы – формирование условий для безопасной эксплуатации ядерного объекта. В процессе исследования проводился анализ нормативно-правовых документов по вопросам организации и функционирования систем физической защиты и систем учета и контроля ядерных материалов на ядерном объекте, формирование требований к оснащению элементами комплекса инженерно- технических средств физической защиты внутренней зоны и периметра ядерного объекта. Был проведен анализ спектральных характеристик неизвестного источника ионизирующего излучения. В результате был получен проект по оснащению комплексом инженерно- технических средств физической защиты периметра и внутренней зоны ядерного объекта. Был определен изотопный состав неизвестного источника ионизирующего излучения, подсчитана его масса и активность.The object of research is the organization and functioning of physical protection systems. The work purpose – to create conditions for the safe operation of a nuclear facility. In the process of investigation the analysis of normative-legal documents on the organization and functioning of systems of physical protection and systems for accounting and control of nuclear materials at the nuclear facility, development of requirements for equipping of the complex of technical means of physical protection of the internal area and perimeter of a nuclear facility. An analysis was conducted of the spectral characteristics of an unknown source of ionizing radiation. The result was obtained the project to equip the complex of technical means of physical protection of the perimeter and internal zones of a nuclear facility. Was determined the isotopic composition of an unknown source of ionizing radiation, calculated its mass and activity
Long distance quantum teleportation of qubits from photons at 1300 nm to photons at 1550 nm wavelength
Elementary 2-dimensional quantum states (qubits) encoded in 1300 nm
wavelength photons are teleported onto 1550 nm photons. The use of
telecommunication wavelengths enables to take advantage of standard optical
fibre and permits to teleport from one lab to a distant one, 55 m away,
connected by 2 km of fibre. A teleportation fidelity of 81.2 % is reported.
This is large enough to demonstrate the principles of quantum teleportation, in
particular that entanglement is exploited. This experiment constitutes a first
step towards a quantum repeater.Comment: 7 pages, 5 figures, Extended version of Nature lette
Entanglement between more than two hundred macroscopic atomic ensembles in a solid
We create a multi-partite entangled state by storing a single photon in a
crystal that contains many large atomic ensembles with distinct resonance
frequencies. The photon is re-emitted at a well-defined time due to an
interference effect analogous to multi-slit diffraction. We derive a lower
bound for the number of entangled ensembles based on the contrast of the
interference and the single-photon character of the input, and we
experimentally demonstrate entanglement between over two hundred ensembles,
each containing a billion atoms. In addition, we illustrate the fact that each
individual ensemble contains further entanglement. Our results are the first
demonstration of entanglement between many macroscopic systems in a solid and
open the door to creating even more complex entangled states.Comment: 10 pages, 8 figures; see also parallel submission by Frowis et a
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