434 research outputs found
Practical security bounds against the Trojan-horse attack in quantum key distribution
In the quantum version of a Trojan-horse attack, photons are injected into
the optical modules of a quantum key distribution system in an attempt to read
information direct from the encoding devices. To stop the Trojan photons, the
use of passive optical components has been suggested. However, to date, there
is no quantitative bound that specifies such components in relation to the
security of the system. Here, we turn the Trojan-horse attack into an
information leakage problem. This allows us quantify the system security and
relate it to the specification of the optical elements. The analysis is
supported by the experimental characterization, within the operation regime, of
reflectivity and transmission of the optical components most relevant to
security.Comment: 18 pages, 11 figures. Some typos correcte
Optical transmitter tunable over a 65-nm wavelength range around 1550 nm for quantum key distribution
The ability to create phase-controlled pulses of light with wavelength
tunability has applications spanning quantum and classical communications
networks. Traditionally, optical transmitters are able to either produce
phase-controlled pulses at a fixed wavelength or require a chain of bulky and
expensive external modulators to convert wavelength tunable continuous-wave
light into optical pulses. One technology of great interest is quantum key
distribution (QKD), a technology for generating perfectly random keys at remote
nodes to ensure secure communications. Environments such as data centers, where
the user needs change regularly, will require adaptability in the deployment of
QKD to integrate into classical optical networks. Here we propose and
demonstrate an alternative quantum transmitter design consisting of a
multimodal Fabry-Perot laser optically injection locked by a wavelength tunable
laser. The transmitter is able to produce phase-controlled optical pulses at
GHz speeds with a tunable wavelength range of >65nm centered at 1550 nm. With
this transmitter, we perform proof-of-principle QKD with secure bit rates of
order Mb/s
Coulomb Zero-Bias Anomaly: A Semiclassical Calculation
Effective action is proposed for the problem of Coulomb blocking of
tunneling. The approach is well suited to deal with the ``strong coupling''
situation near zero bias, where perturbation theory diverges. By a
semiclassical treatment, we reduce the physics to that of electrodynamics in
imaginary time, and express the anomaly through exact conductivity of the
system and exact interaction. For the diffusive anomaly, we
compare the result with the perturbation theory of Altshuler, Aronov, and Lee.
For the metal-insulator transition we derive exact relation of the anomaly and
critical exponent of conductivity.Comment: 9 pages, RevTeX 3.
A High Speed, Post-Processing Free, Quantum Random Number Generator
A quantum random number generator (QRNG) based on gated single photon
detection of an InGaAs photodiode at GHz frequency is demonstrated. Owing to
the extremely long coherence time of each photon, each photons' wavefuntion
extends over many gating cycles of the photodiode. The collapse of the photon
wavefunction on random gating cycles as well as photon random arrival time
detection events are used to generate sequences of random bits at a rate of
4.01 megabits/s. Importantly, the random outputs are intrinsically bias-free
and require no post-processing procedure to pass random number statistical
tests, making this QRNG an extremely simple device
Orthorhombically Mixed s and d Wave Superconductivity and Josephson Tunneling
The effect of orthorhombicity on Josephson tunneling in high T
superconductors such as YBCO is studied for both single crystals and highly
twinned crystals. It is shown that experiments on highly twinned crystals
experimentally determine the symmetry of the superconducting twin boundaries
(which can be either even or odd with respect to a reflection in the twinning
plane). Conversely, Josephson experiments on highly twinned crystals can not
experimentally determine whether the superconductivity is predominantly
-wave or predominantly -wave. The direct experimental determination of
the order-parameter symmetry by Josephson tunneling in YBCO thus comes from the
relatively few experiments which have been carried out on untwinned single
crystals.Comment: 5 pages, RevTeX file, 1 figure available on request
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