18 research outputs found
Optimum design for BB84 quantum key distribution in tree-type passive optical networks
We show that there is a tradeoff between the useful key distribution bit rate
and the total length of deployed fiber in tree-type passive optical networks
for BB84 quantum key distribution applications. A two stage splitting
architecture where one splitting is carried in the central office and a second
in the outside plant and figure of merit to account for the tradeoff are
proposed. We find that there is an optimum solution for the splitting ratios of
both stages in the case of Photon Number Splitting (PNS) attacks and Decoy
State transmission. We then analyze the effects of the different relevant
physical parameters of the PON on the optimum solution.Comment: Published in the Journal of the Optical Society of America
Ramsey spectroscopy of high-contrast CPT resonances with push-pull optical pumping in Cs vapor
We report the detection of high-contrast and narrow Coherent Population
Trapping (CPT) Ramsey fringes in a Cs vapor cell using a simple-architecture
laser system. The latter allows the combination of push-pull optical pumping
(PPOP) and a temporal Ramsey-like pulsed interrogation. An originality of the
optics package is the use of a single Mach-Zehnder electro-optic modulator (MZ
EOM) both for optical sidebands generation and light switch for pulsed
interaction. Typical Ramsey fringes with a linewidth of 166 Hz and a contrast
of 33 % are detected in a cm-scale buffer-gas filled Cs vapor cell. This
technique could be interesting for the development of high-performance and low
power consumption compact vapor cell clocks based on CPT.Comment: 9 pages, 8 figure
Coherent Population Trapping Resonances in Buffer Gas-filled Cs Vapor Cells with Push-Pull Optical Pumping
We report on a theoretical study and experimental characterization of
coherent population trapping (CPT) resonances in buffer gas-filled vapor cells
with push-pull optical pumping (PPOP) on Cs D1 line. We point out that the
push-pull interaction scheme is identical to the so-called lin per lin
polarization scheme. Expressions of the relevant dark states, as well as of
absorption, are reported. The experimental setup is based on the combination of
a distributed feedback (DFB) diode laser, a pigtailed intensity Mach-Zehnder
electro-optic modulator (MZ EOM) for optical sidebands generation and a
Michelson-like interferometer. A microwave technique to stabilize the transfer
function operating point of the MZ EOM is implemented for proper operation. A
CPT resonance contrast as high as 78% is reported in a cm-scale cell for the
magnetic-field insensitive clock transition. The impact of the laser intensity
on the CPT clock signal key parameters (linewidth - contrast -
linewidth/contrast ratio) is reported for three different cells with various
dimensions and buffer gas contents. The potential of the PPOP technique for the
development of high-performance atomic vapor cell clocks is discussed.Comment: 28 pages, 12 figure
Quantum key distribution over 30km of standard fiber using energy-time entangled photon pairs: a comparison of two chromatic dispersion reduction methods
We present a full implementation of a quantum key distribution system using
energy-time entangled photon pairs and functioning with a 30km standard telecom
fiber quantum channel. Two bases of two orthogonal states are implemented and
the setup is quite robust to environmental constraints such as temperature
variation. Two different ways to manage chromatic dispersion in the quantum
channel are discussed.Comment: 10 pages, 4 figure
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
Subcarrier Wave Quantum Key Distribution in Telecommunication Network with Bitrate 800 kbit/s
In the course of work on creating the first quantum communication network in Russia we demonstrated quantum key distribution in metropolitan optical network infrastructure. A single-pass subcarrier wave quantum cryptography scheme was used in the experiments. BB84 protocol with strong reference was chosen for performing key distribution. The registered sifted key rate in an optical cable with 1.5 dB loss was 800 Kbit/s. Signal visibility exceeded 98%, and quantum bit error rate value was 1%. The achieved result is a record for this type of systems
Quantum Cryptography
Quantum cryptography could well be the first application of quantum mechanics
at the individual quanta level. The very fast progress in both theory and
experiments over the recent years are reviewed, with emphasis on open questions
and technological issues.Comment: 55 pages, 32 figures; to appear in Reviews of Modern Physic
Transmission quantique de clés de cryptage en milieu aérien par codage en phase de bandes latérales de modulation
L'étude présentée concerne un procédé de distribution quantique de clés de cryptage utilisant des états cohérents et la mise au point d'un système de transmission aérien. Le système de cryptage exploite les propriétés d'interférence à un photon dans deux bandes latérales de modulation, qui contiennent chacune en moyenne 0,1 photon. Les probabilités de détecter un photon dans chacune des bandes de modulation varient de façon complémentaire en fonction du déphasage induit entre l'émetteur et le récepteur. Cette méthode permet d'exploiter le protocole à 4 états de distribution de clé