433 research outputs found
Quantum Eavesdropping without Interception: An Attack Exploiting the Dead Time of Single Photon Detectors
The security of quantum key distribution (QKD) can easily be obscured if the
eavesdropper can utilize technical imperfections of the actual implementation.
Here we describe and experimentally demonstrate a very simple but highly
effective attack which even does not need to intercept the quantum channel at
all. Only by exploiting the dead time effect of single photon detectors the
eavesdropper is able to gain (asymptotically) full information about the
generated keys without being detected by state-of-the-art QKD protocols. In our
experiment, the eavesdropper inferred up to 98.8% of the key correctly, without
increasing the bit error rate between Alice and Bob significantly. Yet, we find
an evenly simple and effective countermeasure to inhibit this and similar
attacks
Feasibility of free space quantum key distribution with coherent polarization states
We demonstrate for the first time the feasibility of free space quantum key
distribution with continuous variables under real atmospheric conditions. More
specifically, we transmit coherent polarization states over a 100m free space
channel on the roof of our institute's building. In our scheme, signal and
local oscillator are combined in a single spatial mode which auto-compensates
atmospheric fluctuations and results in an excellent interference. Furthermore,
the local oscillator acts as spatial and spectral filter thus allowing
unrestrained daylight operation.Comment: 12 pages, 8 figures, extensions in sections 2, 3.1, 3.2 and 4. This
is an author-created, un-copyedited version of an article accepted for
publication in New Journal of Physics (Special Issue on Quantum Cryptography:
Theory and Practice). IOP Publishing Ltd is not responsible for any errors or
omissions in this version of the manuscript or any version derived from i
Distributing entanglement and single photons through an intra-city, free-space quantum channel
We have distributed entangled photons directly through the atmosphere to a
receiver station 7.8 km away over the city of Vienna, Austria at night.
Detection of one photon from our entangled pairs constitutes a triggered single
photon source from the sender. With no direct time-stable connection, the two
stations found coincidence counts in the detection events by calculating the
cross-correlation of locally-recorded time stamps shared over a public internet
channel. For this experiment, our quantum channel was maintained for a total of
40 minutes during which time a coincidence lock found approximately 60000
coincident detection events. The polarization correlations in those events
yielded a Bell parameter, S=2.27/pm0.019, which violates the CHSH-Bell
inequality by 14 standard deviations. This result is promising for
entanglement-based free-space quantum communication in high-density urban
areas. It is also encouraging for optical quantum communication between ground
stations and satellites since the length of our free-space link exceeds the
atmospheric equivalent.Comment: 8 pages including 1 figure and 2 tables. The first two authors
contributed equally to this wor
Comparative chromosome painting discloses homologous Segments in distantly related mammals
Comparative chromosome painting, termed ZOO-FISH, using DNA libraries from flow
sorted human chromosomes 1,16,17 and X, and mouse chromosome 11 discloses the
presence of syntenic groups in distantly related mammalian Orders ranging from
primates (Homo sapiens), rodents (Mus musculus), even-toed ungulates (Muntiacus
muntjak vaginalis and Muntiacus reevesi) and whales (Balaenoptera physalus). These
mammalian Orders have evolved separately for 55-80 million years (Myr). We conclude
that ZOO-FISH can be used to generate comparative chromosome maps of a large
number of mammalian species
Nitrogen and sulphur management: challenges for organic sources in temperate agricultural systems
A current global trend towards intensification or specialization of agricultural enterprises has been accompanied by increasing public awareness of associated environmental consequences. Air and water pollution from losses of nutrients, such as nitrogen (N) and sulphur (S), are a major concern. Governments have initiated extensive regulatory frameworks, including various land use policies, in an attempt to control or reduce the losses. This paper presents an overview of critical input and loss processes affecting N and S for temperate climates, and provides some background to the discussion in subsequent papers evaluating specific farming systems. Management effects on potential gaseous and leaching losses, the lack of synchrony between supply of nutrients and plant demand, and options for optimizing the efficiency of N and S use are reviewed. Integration of inorganic and organic fertilizer inputs and the equitable re-distribution of nutrients from manure are discussed. The paper concludes by highlighting a need for innovative research that is also targeted to practical approaches for reducing N and S losses, and improving the overall synchrony between supply and demand
Controlling a superconducting nanowire single-photon detector using tailored bright illumination
We experimentally demonstrate that a superconducting nanowire single-photon
detector is deterministically controllable by bright illumination. We found
that bright light can temporarily make a large fraction of the nanowire length
normally-conductive, can extend deadtime after a normal photon detection, and
can cause a hotspot formation during the deadtime with a highly nonlinear
sensitivity. In result, although based on different physics, the
superconducting detector turns out to be controllable by virtually the same
techniques as avalanche photodiode detectors. As demonstrated earlier, when
such detectors are used in a quantum key distribution system, this allows an
eavesdropper to launch a detector control attack to capture the full secret key
without being revealed by to many errors in the key.Comment: Expanded discussions, updated references. 9 pages, 8 figure
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