251 research outputs found
Quantum random number generation on a mobile phone
Quantum random number generators (QRNGs) can significantly improve the
security of cryptographic protocols, by ensuring that generated keys cannot be
predicted. However, the cost, size, and power requirements of current QRNGs has
prevented them from becoming widespread. In the meantime, the quality of the
cameras integrated in mobile telephones has improved significantly, so that now
they are sensitive to light at the few-photon level. We demonstrate how these
can be used to generate random numbers of a quantum origin
Finite-key analysis on the 1-decoy state QKD protocol
It has been shown that in the asymptotic case of infinite-key length the
2-decoy state QKD protocol outperforms the 1-decoy state protocol. Here, we
present a finite-key analysis of the 1-decoy method. Interestingly, we find
that for practical block sizes of up to bits, the 1-decoy protocol
achieves for almost all experimental settings higher secret key rates than the
2-decoy protocol. Since using only one decoy is also easier to implement, we
conclude that it is the best choice for practical QKD.Comment: 6 pages, 7 figures, Pape
Perfectly secure steganography: hiding information in the quantum noise of a photograph
We show that the quantum nature of light can be used to hide a secret message
within a photograph. Using this physical principle we achieve
information-theoretic secure steganography, which had remained elusive until
now. The protocol is such that the digital picture in which the secret message
is embedded is perfectly undistinguishable from an ordinary photograph. This
implies that, on a fundamental level, it is impossible to discriminate a
private communication from an exchange of photographs.Comment: 5 pages, 3 figures + appendix : 5 pages, 6 figure
Narrowband Photon Pair Source for Quantum Networks
We demonstrate a compact photon pair source based on a periodically poled
lithium niobate nonlinear crystal in a cavity. The cavity parameters are chosen
such that the emitted photon pair modes can be matched in the region of telecom
ultra dense wavelength division multiplexing (U-DWDM) channel spacings. This
approach provides efficient, low-loss, mode selection that is compatible with
standard telecommunication networks. Photons with a coherence time of 8.6 ns
(116 MHz) are produced and their purity is demonstrated. A source brightness of
134 pairs(s.mW.MHz) is reported. The high level of purity and
compatibility with standard telecom networks is of great importance for complex
quantum communication networks
Quantum random number generation for 1.25 GHz quantum key distribution systems
Security proofs of quantum key distribution (QKD) systems usually assume that
the users have access to source of perfect randomness. State-of-the-art QKD
systems run at frequencies in the GHz range, requiring a sustained GHz rate of
generation and acquisition of quantum random numbers. In this paper we
demonstrate such a high speed random number generator. The entropy source is
based on amplified spontaneous emission from an erbium-doped fibre, which is
directly acquired using a standard small form-factor pluggable (SFP) module.
The module connects to the Field Programmable Gate Array (FPGA) of a QKD
system. A real-time randomness extractor is implemented in the FPGA and
achieves a sustained rate of 1.25 Gbps of provably random bits.Comment: 6 pages, 8 figure
High efficiency coupling of photon pairs in practice
Multi-photon and quantum communication experiments such as loophole-free Bell
tests and device independent quantum key distribution require entangled photon
sources which display high coupling efficiency. In this paper we put forward a
simple quantum theoretical model which allows the experimenter to design a
source with high pair coupling efficiency. In particular we apply this approach
to a situation where high coupling has not been previously obtained: we
demonstrate a symmetric coupling efficiency of more than 80% in a highly
frequency non-degenerate configuration. Furthermore, we demonstrate this
technique in a broad range of configurations, i.e. in continuous wave and
pulsed pump regimes, and for different nonlinear crystals
Detector-Device-Independent Quantum Key Distribution
Recently, a quantum key distribution (QKD) scheme based on entanglement
swapping, called measurement-device-independent QKD (mdiQKD), was proposed to
bypass all detector side-channel attacks. While mdiQKD is conceptually elegant
and offers a supreme level of security, the experimental complexity is
challenging for practical systems. For instance, it requires interference
between two widely separated independent single-photon sources, and the rates
are dependent on detecting two photons - one from each source. Here we
experimentally demonstrate a QKD scheme that removes the need for a two-photon
system and instead uses the idea of a two-qubit single-photon (TQSP) to
significantly simplify the implementation and improve the efficiency of mdiQKD
in several aspects.Comment: 5 pages + 3 figure
Quantum Metropolitan Optical Network based on Wavelength Division Multiplexing
Quantum Key Distribution (QKD) is maturing quickly. However, the current
approaches to its application in optical networks make it an expensive
technology. QKD networks deployed to date are designed as a collection of
point-to-point, dedicated QKD links where non-neighboring nodes communicate
using the trusted repeater paradigm. We propose a novel optical network model
in which QKD systems share the communication infrastructure by wavelength
multiplexing their quantum and classical signals. The routing is done using
optical components within a metropolitan area which allows for a dynamically
any-to-any communication scheme. Moreover, it resembles a commercial telecom
network, takes advantage of existing infrastructure and utilizes commercial
components, allowing for an easy, cost-effective and reliable deployment.Comment: 23 pages, 8 figure
Detector-device-independent QKD: security analysis and fast implementation
One of the most pressing issues in quantum key distribution (QKD) is the
problem of detector side- channel attacks. To overcome this problem,
researchers proposed an elegant "time-reversal" QKD protocol called
measurement-device-independent QKD (MDI-QKD), which is based on time-reversed
entanglement swapping. However, MDI-QKD is more challenging to implement than
standard point- to-point QKD. Recently, an intermediary QKD protocol called
detector-device-independent QKD (DDI-QKD) has been proposed to overcome the
drawbacks of MDI-QKD, with the hope that it would eventually lead to a more
efficient detector side-channel-free QKD system. Here, we analyze the security
of DDI-QKD and elucidate its security assumptions. We find that DDI-QKD is not
equivalent to MDI-QKD, but its security can be demonstrated with reasonable
assumptions. On the more practical side, we consider the feasibility of DDI-QKD
and present a fast experimental demonstration (clocked at 625 MHz), capable of
secret key exchange up to more than 90 km.Comment: 9 pages, 4 figure
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