22 research outputs found
Fast optical source for quantum key distribution based on semiconductor optical amplifiers
A novel integrated optical source capable of emitting faint pulses with
different polarization states and with different intensity levels at 100 MHz
has been developed. The source relies on a single laser diode followed by four
semiconductor optical amplifiers and thin film polarizers, connected through a
fiber network. The use of a single laser ensures high level of
indistinguishability in time and spectrum of the pulses for the four different
polarizations and three different levels of intensity. The applicability of the
source is demonstrated in the lab through a free space quantum key distribution
experiment which makes use of the decoy state BB84 protocol. We achieved a
lower bound secure key rate of the order of 3.64 Mbps and a quantum bit error
ratio as low as while the lower bound secure key rate
became 187 bps for an equivalent attenuation of 35 dB. To our knowledge, this
is the fastest polarization encoded QKD system which has been reported so far.
The performance, reduced size, low power consumption and the fact that the
components used can be space qualified make the source particularly suitable
for secure satellite communication
The Case for Quantum Key Distribution
Quantum key distribution (QKD) promises secure key agreement by using quantum
mechanical systems. We argue that QKD will be an important part of future
cryptographic infrastructures. It can provide long-term confidentiality for
encrypted information without reliance on computational assumptions. Although
QKD still requires authentication to prevent man-in-the-middle attacks, it can
make use of either information-theoretically secure symmetric key
authentication or computationally secure public key authentication: even when
using public key authentication, we argue that QKD still offers stronger
security than classical key agreement.Comment: 12 pages, 1 figure; to appear in proceedings of QuantumComm 2009
Workshop on Quantum and Classical Information Security; version 2 minor
content revision
Atmospheric Channel Characteristics for Quantum Communication with Continuous Polarization Variables
We investigate the properties of an atmospheric channel for free space
quantum communication with continuous polarization variables. In our
prepare-and-measure setup, coherent polarization states are transmitted through
an atmospheric quantum channel of 100m length on the roof of our institute's
building. The signal states are measured by homodyne detection with the help of
a local oscillator (LO) which propagates in the same spatial mode as the
signal, orthogonally polarized to it. Thus the interference of signal and LO is
excellent and atmospheric fluctuations are autocompensated. The LO also acts as
spatial and spectral filter, which allows for unrestrained daylight operation.
Important characteristics for our system are atmospheric channel influences
that could cause polarization, intensity and position excess noise. Therefore
we study these influences in detail. Our results indicate that the channel is
suitable for our quantum communication system in most weather conditions.Comment: 6 pages, 4 figures, submitted to Applied Physics B following an
invitation for the special issue "Selected Papers Presented at the 2009
Spring Meeting of the Quantum Optics and Photonics Section of the German
Physical Society
Free-Space distribution of entanglement and single photons over 144 km
Quantum Entanglement is the essence of quantum physics and inspires
fundamental questions about the principles of nature. Moreover it is also the
basis for emerging technologies of quantum information processing such as
quantum cryptography, quantum teleportation and quantum computation. Bell's
discovery, that correlations measured on entangled quantum systems are at
variance with a local realistic picture led to a flurry of experiments
confirming the quantum predictions. However, it is still experimentally
undecided whether quantum entanglement can survive global distances, as
predicted by quantum theory. Here we report the violation of the
Clauser-Horne-Shimony-Holt (CHSH) inequality measured by two observers
separated by 144 km between the Canary Islands of La Palma and Tenerife via an
optical free-space link using the Optical Ground Station (OGS) of the European
Space Agency (ESA). Furthermore we used the entangled pairs to generate a
quantum cryptographic key under experimental conditions and constraints
characteristic for a Space-to-ground experiment. The distance in our experiment
exceeds all previous free-space experiments by more than one order of magnitude
and exploits the limit for ground-based free-space communication; significantly
longer distances can only be reached using air- or space-based platforms. The
range achieved thereby demonstrates the feasibility of quantum communication in
space, involving satellites or the International Space Station (ISS).Comment: 10 pages including 2 figures and 1 table, Corrected typo
Space-QUEST: Experiments with quantum entanglement in space
The European Space Agency (ESA) has supported a range of studies in the field
of quantum physics and quantum information science in space for several years,
and consequently we have submitted the mission proposal Space-QUEST (Quantum
Entanglement for Space Experiments) to the European Life and Physical Sciences
in Space Program. We propose to perform space-to-ground quantum communication
tests from the International Space Station (ISS). We present the proposed
experiments in space as well as the design of a space based quantum
communication payload.Comment: 4 pages, 1 figure, accepted for the 59th International Astronautical
Congress (IAC) 200
Methodology for Traffic Analysis and ISL Capacity Dimensioning in Broadband Satellite Constellations Using Optical WDM Networking
Experimental demonstration of free-space decoy-state quantum key distribution over 144 km
10.1109/CLEOE-IQEC.2007.4386755Conference on Lasers and Electro-Optics Europe - Technical Digest-85PN