88 research outputs found
Detector dead-time effects and paralyzability in high-speed quantum key distribution
Recent advances in quantum key distribution (QKD) have given rise to systems
that operate at transmission periods significantly shorter than the dead times
of their component single-photon detectors. As systems continue to increase in
transmission rate, security concerns associated with detector dead times can
limit the production rate of sifted bits. We present a model of high-speed QKD
in this limit that identifies an optimum transmission rate for a system with
given link loss and detector response characteristics
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
Quantum key distribution with 1.25 Gbps clock synchronization
We have demonstrated the exchange of sifted quantum cryptographic key over a
730 meter free-space link at rates of up to 1.0 Mbps, two orders of magnitude
faster than previously reported results. A classical channel at 1550 nm
operates in parallel with a quantum channel at 845 nm. Clock recovery
techniques on the classical channel at 1.25 Gbps enable quantum transmission at
up to the clock rate. System performance is currently limited by the timing
resolution of our silicon avalanche photodiode detectors. With improved
detector resolution, our technique will yield another order of magnitude
increase in performance, with existing technology.Comment: 6 pages, 3 figures, 99 kB .pdf documen
High-fidelity transmission of entanglement over a high-loss freespace channel
Quantum entanglement enables tasks not possible in classical physics. Many
quantum communication protocols require the distribution of entangled states
between distant parties. Here we experimentally demonstrate the successful
transmission of an entangled photon pair over a 144 km free-space link. The
received entangled states have excellent, noise-limited fidelity, even though
they are exposed to extreme attenuation dominated by turbulent atmospheric
effects. The total channel loss of 64 dB corresponds to the estimated
attenuation regime for a two-photon satellite quantum communication scenario.
We confirm that the received two-photon states are still highly entangled by
violating the CHSH inequality by more than 5 standard deviations. From a
fundamental point of view, our results show that the photons are virtually not
subject to decoherence during their 0.5 ms long flight through air, which is
encouraging for future world-wide quantum communication scenarios.Comment: 5 pages, 3 figures, replaced paper with published version, added
journal referenc
High Efficiency Planar Geometry Germanium-on-silicon Single-photon Avalanche Diode Detectors
This paper presents the performance of 26 μm and 50 μm diameter planar Ge-on-Si single-photon avalanche diode (SPAD) detectors. The addition of germanium in these detectors extends the spectral range into the short-wave infrared (SWIR) region, beyond the capability of already well-established Si SPAD devices. There are several advantages for extending the spectral range into the SWIR region including: reduced eye-safety laser threshold, greater attainable ranges, and increased depth resolution in range finding applications, in addition to the enhanced capability to image through obscurants such as fog and smoke. The time correlated single-photon counting (TCSPC) technique has been utilized to observe record low dark count rates, below 100 kHz at a temperature of 125 K for up to a 6.6 % excess bias, for the 26 μm diameter devices. Under identical experimental conditions, in terms of excess bias and temperature, the 50 μm diameter device consistently demonstrates dark count rates a factor of 4 times greater than 26 μm diameter devices, indicating that the dark count rate is proportional to the device volume. Single-photon detection efficiencies of up to ~ 29 % were measured at a wavelength of 1310 nm at 125 K. Noise equivalent powers (NEP) down to 9.8 × 10-17 WHz-1/2 and jitters < 160 ps are obtainable, both significantly lower than previous 100 μm diameter planar geometry devices, demonstrating the potential of these devices for highly sensitive and high-speed imaging in the SWIR
Prominent Human Health Impacts from Several Marine Microbes: History, Ecology, and Public Health Implications
This paper overviews several examples of important public health impacts by marine microbes and directs readers to the extensive literature germane to these maladies. These examples include three types of dinoflagellates (Gambierdiscus spp., Karenia brevis, and Alexandrium fundyense), BMAA-producing cyanobacteria, and infectious microbes. The dinoflagellates are responsible for ciguatera fish poisoning, neurotoxic shellfish poisoning, and paralytic shellfish poisoning, respectively, that have plagued coastal populations over time. Research interest on the potential for marine cyanobacteria to contribute BMAA into human food supplies has been derived by BMAA's discovery in cycad seeds and subsequent implication as the putative cause of amyotrophic lateral sclerosis/parkinsonism dementia complex among the Chamorro people of Guam. Recent UPLC/MS analyses indicate that recent reports that BMAA is prolifically distributed among marine cyanobacteria at high concentrations may be due to analyte misidentification in the analytical protocols being applied for BMAA. Common infectious microbes (including enterovirus, norovirus, Salmonella, Campylobacter, Shigella, Staphylococcus aureus, Cryptosporidium, and Giardia) cause gastrointestinal and skin-related illness. These microbes can be introduced from external human and animal sources, or they can be indigenous to the marine environment
An approach for particle sinking velocity measurements in the 3–400 μm size range and considerations on the effect of temperature on sinking rates
The flux of organic particles below the mixed layer is one major pathway of carbon from the surface into the deep ocean. The magnitude of this export flux depends on two major processes—remineralization rates and sinking velocities. Here, we present an efficient method to measure sinking velocities of particles in the size range from approximately 3–400 μm by means of video microscopy (FlowCAM®). The method allows rapid measurement and automated analysis of mixed samples and was tested with polystyrene beads, different phytoplankton species, and sediment trap material. Sinking velocities of polystyrene beads were close to theoretical values calculated from Stokes’ Law. Sinking velocities of the investigated phytoplankton species were in reasonable agreement with published literature values and sinking velocities of material collected in sediment trap increased with particle size. Temperature had a strong effect on sinking velocities due to its influence on seawater viscosity and density. An increase in 9 °C led to a measured increase in sinking velocities of ~40 %. According to this temperature effect, an average temperature increase in 2 °C as projected for the sea surface by the end of this century could increase sinking velocities by about 6 % which might have feedbacks on carbon export into the deep ocean
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