111,470 research outputs found
Security of quantum key distribution with imperfect phase randomisation
The performance of quantum key distribution (QKD) is severely limited by
multiphoton emissions, due to the photon-number-splitting attack. The most
efficient solution, the decoy-state method, requires that the phases of all
transmitted pulses are independent and uniformly random. In practice, however,
these phases are often correlated, especially in high-speed systems, which
opens a security loophole. Here, we address this pressing problem by providing
a security proof for decoy-state QKD with correlated phases that offers key
rates close to the ideal scenario. Our work paves the way towards
high-performance secure QKD with practical laser sources, and may have
applications beyond QKD.Comment: 22 pages, 1 figure. v3: Updated to Accepted Manuscrip
Johnson(-like)-Noise-Kirchhoff-Loop Based Secure Classical Communicator Characteristics, for Ranges of Two to Two Thousand Kilometers, via Model-Line
A pair of Kirchhoff-Loop-Johnson(-like)-Noise communicators, which is able to
work over variable ranges, was designed and built. Tests have been carried out
on a model-line performance characteristics were obtained for ranges beyond the
ranges of any known direct quantum communication channel and they indicate
unrivalled signal fidelity and security performance of the exchanged raw key
bits. This simple device has single-wire secure key generation and sharing
rates of 0.1, 1, 10, and 100 bit/second for corresponding copper wire
diameters/ranges of 21 mm / 2000 km, 7 mm / 200 km, 2.3 mm / 20 km, and 0.7 mm
/ 2 km, respectively and it performs with 0.02% raw-bit error rate (99.98 %
fidelity). The raw-bit security of this practical system significantly
outperforms raw-bit quantum security. Current injection breaking tests show
zero bit eavesdropping ability without triggering the alarm signal, therefore
no multiple measurements are needed to build an error statistics to detect the
eavesdropping as in quantum communication. Wire resistance based breaking tests
of Bergou-Scheuer-Yariv type give an upper limit of eavesdropped raw bit ratio
of 0.19 % and this limit is inversely proportional to the sixth power of cable
diameter. Hao's breaking method yields zero (below measurement resolution)
eavesdropping information.Comment: Featured in New Scientist, Jason Palmer, May 23, 2007.
http://www.ece.tamu.edu/%7Enoise/news_files/KLJN_New_Scientist.pdf
Corresponding Plenary Talk at the 4th International Symposium on Fluctuation
and Noise, Florence, Italy (May 23, 2007
Integrated Silicon Photonics for High-Speed Quantum Key Distribution
Integrated photonics offers great potential for quantum communication devices
in terms of complexity, robustness and scalability. Silicon photonics in
particular is a leading platform for quantum photonic technologies, with
further benefits of miniaturisation, cost-effective device manufacture and
compatibility with CMOS microelectronics. However, effective techniques for
high-speed modulation of quantum states in standard silicon photonic platforms
have been limited. Here we overcome this limitation and demonstrate high-speed
low-error quantum key distribution modulation with silicon photonic devices
combining slow thermo-optic DC biases and fast (10~GHz bandwidth)
carrier-depletion modulation. The ability to scale up these integrated circuits
and incorporate microelectronics opens the way to new and advanced integrated
quantum communication technologies and larger adoption of quantum-secured
communications
The Quantum Frontier
The success of the abstract model of computation, in terms of bits, logical
operations, programming language constructs, and the like, makes it easy to
forget that computation is a physical process. Our cherished notions of
computation and information are grounded in classical mechanics, but the
physics underlying our world is quantum. In the early 80s researchers began to
ask how computation would change if we adopted a quantum mechanical, instead of
a classical mechanical, view of computation. Slowly, a new picture of
computation arose, one that gave rise to a variety of faster algorithms, novel
cryptographic mechanisms, and alternative methods of communication. Small
quantum information processing devices have been built, and efforts are
underway to build larger ones. Even apart from the existence of these devices,
the quantum view on information processing has provided significant insight
into the nature of computation and information, and a deeper understanding of
the physics of our universe and its connections with computation.
We start by describing aspects of quantum mechanics that are at the heart of
a quantum view of information processing. We give our own idiosyncratic view of
a number of these topics in the hopes of correcting common misconceptions and
highlighting aspects that are often overlooked. A number of the phenomena
described were initially viewed as oddities of quantum mechanics. It was
quantum information processing, first quantum cryptography and then, more
dramatically, quantum computing, that turned the tables and showed that these
oddities could be put to practical effect. It is these application we describe
next. We conclude with a section describing some of the many questions left for
future work, especially the mysteries surrounding where the power of quantum
information ultimately comes from.Comment: Invited book chapter for Computation for Humanity - Information
Technology to Advance Society to be published by CRC Press. Concepts
clarified and style made more uniform in version 2. Many thanks to the
referees for their suggestions for improvement
A balanced homodyne detector for high-rate Gaussian-modulated coherent-state quantum key distribution
We discuss excess noise contributions of a practical balanced homodyne
detector in Gaussian-modulated coherent-state (GMCS) quantum key distribution
(QKD). We point out the key generated from the original realistic model of GMCS
QKD may not be secure. In our refined realistic model, we take into account
excess noise due to the finite bandwidth of the homodyne detector and the
fluctuation of the local oscillator. A high speed balanced homodyne detector
suitable for GMCS QKD in the telecommunication wavelength region is built and
experimentally tested. The 3dB bandwidth of the balanced homodyne detector is
found to be 104MHz and its electronic noise level is 13dB below the shot noise
at a local oscillator level of 8.5*10^8 photon per pulse. The secure key rate
of a GMCS QKD experiment with this homodyne detector is expected to reach
Mbits/s over a few kilometers.Comment: 22 pages, 11 figure
Totally secure classical networks with multipoint telecloning (teleportation) of classical bits through loops with Johnson-like noise
First, we show a new inexpensive defense against intruders and the
man-in-the-middle attack in the Kirchhoff's-loop-Johnson-like-noise (KLJN)
cipher. Then instead of point-to-point communication, we propose a high
efficiency, secure network. The (in the idealistic case totally secure)
classical network is based on an improved version of the KLJN cipher. The
network consists of two parallel networks: i) a chain-like network of securely
communicating, electrically isolated Kirchhoff-loops with Johnson-like noise
and driven by a specific switching process of the resistances; ii) and a
regular non-secure data network with a Coordinator-server. If the classical
network is fast enough, the chain-like network of N communicators can generate
and share an N bit long secret key within a single clock period of the ciphers
and that implies a significant speed-up compared to the point-to-point key
exchanges used by quantum communication or RSA-like key exchange methods. This
is a teleportation-type multiple telecloning of the classical information bit
because the information transfer can take place without the actual presence of
the information bit at the intermediate points of the network. With similar
quantum schemes the telecloning of classical bits via quantum communicator
networks without telecloning the quantum states is also possible.Comment: Quantum-based network application added. 13 page
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