41 research outputs found
Experimental polarization encoded quantum key distribution over optical fibres with real-time continuous birefringence compensation
In this paper we demonstrate an active polarization drift compensation scheme
for optical fibres employed in a quantum key distribution experiment with
polarization encoded qubits. The quantum signals are wavelength multiplexed in
one fibre along with two classical optical side channels that provide the
control information for the polarization compensation scheme. This set-up
allows us to continuously track any polarization change without the need to
interrupt the key exchange. The results obtained show that fast polarization
rotations of the order of 40*pi rad/s are effectively compensated for. We
demonstrate that our set-up allows continuous quantum key distribution even in
a fibre stressed by random polarization fluctuations. Our results pave the way
for Bell-state measurements using only linear optics with parties separated by
long-distance optical fibres
Polarization-stable long-distance interference of independent photons for quantum communications
Interference between fully-independent faint laser sources over two 8.5-km
full polarization-controlled fiber links was performed, with stable visibility
of 47.8%, an essential step towards practical implementation of quantum
communication protocols
GHz QKD at telecom wavelengths using up-conversion detectors
We have developed a hybrid single photon detection scheme for telecom
wavelengths based on nonlinear sum-frequency generation and silicon
single-photon avalanche diodes (SPADs). The SPAD devices employed have been
designed to have very narrow temporal response, i.e. low jitter, which we can
exploit for increasing the allowable bit rate for quantum key distribution. The
wavelength conversion is obtained using periodically poled Lithium niobate
waveguides (W/Gs). The inherently high efficiency of these W/Gs allows us to
use a continuous wave laser to seed the nonlinear conversion so as to have a
continuous detection scheme. We also present a 1.27GHz qubit repetition rate,
one-way phase encoding, quantum key distribution experiment operating at
telecom wavelengths that takes advantage of this detection scheme. The proof of
principle experiment shows a system capable of MHz raw count rates with a QBER
less than 2% and estimated secure key rates greater than 100 kbit/s over 25 km.Comment: 12 pages, 7 figure
Trapping microparticles in a structured dark focus
We experimentally demonstrate stable trapping and controlled manipulation of
silica microspheres in a structured optical beam consisting of a dark focus
surrounded by light in all directions - the so-called Dark Focus Tweezer.
Results from power spectrum and potential analysis demonstrate the
non-harmonicity of the trapping potential landspace, which is reconstructed
from experimental data in agreement to Lorentz-Mie numerical simulations.
Applications of the dark tweezer in levitated optomechanics and biophysics are
discussed.Comment: Final versio
Proof-of-principle demonstration of measurement-device-independent quantum key distribution using polarization qubits
We perform a proof-of-principle demonstration of the
measurement-device-independent quantum key distribution (MDI-QKD) protocol
using weak coherent states and polarization-encoded qubits over two optical
fiber links of 8.5 km each. Each link was independently stabilized against
polarization drifts using a full-polarization control system employing two
wavelength-multiplexed control channels. A linear-optics-based polarization
Bell-state analyzer was built into the intermediate station, Charlie, which is
connected to both Alice and Bob via the optical fiber links. Using
decoy-states, a lower bound for the secret-key generation rate of 1.04x10^-6
bits/pulse is computed
Dengue Virus Type 4 Phylogenetics in Brazil 2011: Looking beyond the Veil
Dengue Fever and Dengue Hemorrhagic Fever are diseases affecting approximately 100 million people/year and are a major concern in developing countries. In the present study, the phylogenetic relationship of six strains of the first autochthonous cases of DENV-4 infection occurred in Sao Paulo State, Parana State and Rio Grande do Sul State, Brazil, 2011 were studied. Nucleotide sequences of the envelope gene were determined and compared with sequences representative of the genotypes I, II, III and Sylvatic for DEN4 retrieved from GenBank. We employed a Bayesian phylogenetic approach to reconstruct the phylogenetic relationships of Brazilian DENV-4 and we estimated evolutionary rates and dates of divergence for DENV-4 found in Brazil in 2011. All samples sequenced in this study were located in Genotype II. The studied strains are monophyletic and our data suggest that they have been evolving separately for at least 4 to 6 years. Our data suggest that the virus might have been present in the region for some time, without being noticed by Health Surveillance Services due to a low level of circulation and a higher prevalence of DENV-1 and DENV- 2