8,048 research outputs found
Security of "Counterfactual Quantum Cryptography"
Recently, a "counterfactual" quantum key distribution scheme was proposed by
Tae-Gon Noh [1]. In this scheme, two legitimate distant peers may share secret
keys even when the information carriers are not traveled in the quantum
channel. We find that this protocol is equivalent to an entanglement
distillation protocol (EDP). According to this equivalence, a strict security
proof and the asymptotic key bit rate are both obtained when perfect single
photon source is applied and Trojan-horse attack can be detected. We also find
that the security of this scheme is deeply related with not only the bit error
rate but also the yields of photons. And our security proof may shed light on
security of other two-way protocols.Comment: 5 pages, 1 figur
Detection efficiency and noise in semi-device independent randomness extraction protocol
In this paper, we analyze several critical issues in semi-device independent
quantum information processing protocol. In practical experimental realization
randomness generation in that scenario is possible only if the efficiency of
the detectors used is above a certain threshold. Our analysis shows that the
critical detection efficiency is 0.7071 in the symmetric setup, while in the
asymmetric setup if one of the bases has perfect critical detection efficiency
then the other one can be arbitrarily close to 0. We also analyze the
semi-device independent random number generation efficiency based on different
averages of guessing probability. To generate more randomness, the proper
averaging method should be applied. Its choice depends on the value of a
certain dimension witness. More importantly, the general analytical
relationship between the maximal average guessing probability and dimension
witness is given
Quantum discord of ensemble of quantum states
We highlight an information-theoretic meaning of quantum discord as the gap
between the ac- cessible information and the Holevo bound in the framework of
ensemble of quantum states. This complementary relationship implies that a
large amount of pre-existing arguments about the evaluation of quantum discord
can be directly applied to the accessible information and vice versa. For an
ensemble of two pure qubit states, we show that one can evade the optimization
problem with the help of the Koashi-Winter relation. Further, for the general
case (two mixed qubit states), we recover the main results presented by Fuchs
and Caves [Phys. Rev. Lett. 73, 3047 (1994)], but totally from the perspective
of quantum discord. Following this line of thought, we also investigate the
geometric discord as an indicator of quantumness of ensembles in detail.
Finally, we give an example to elucidate the difference between quantum discord
and geometric discord with respect to optimal measurement strategies.Comment: 5 pages, 2 figures. Already submitted. We notice a recent related
work arXiv:1303.465
Security of quantum key distribution with state-dependent imperfections
In practical quantum key distribution (QKD) system, the state preparation and
measurement are imperfect comparing with the ideal BB84 protocol, which are
always state-dependent in practical realizations. If the state-dependent
imperfections can not be regarded as an unitary transformation, it should not
be considered as part of quantum channel noise introduced by the eavesdropper,
the commonly used secret key rate formula GLLP can not be applied
correspondingly. In this paper, the unconditional security of quantum key
distribution with state-dependent imperfection has been analyzed by estimating
the upper bound of the phase error rate about the quantum channel
Two-dimensional Multi-fiber Spectrum Image Correction Based on Machine Learning Techniques
Due to limited size and imperfect of the optical components in a
spectrometer, aberration has inevitably been brought into two-dimensional
multi-fiber spectrum image in LAMOST, which leads to obvious spacial variation
of the point spread functions (PSFs). Consequently, if spatial variant PSFs are
estimated directly , the huge storage and intensive computation requirements
result in deconvolutional spectral extraction method become intractable. In
this paper, we proposed a novel method to solve the problem of spatial
variation PSF through image aberration correction. When CCD image aberration is
corrected, PSF, the convolution kernel, can be approximated by one spatial
invariant PSF only. Specifically, machine learning techniques are adopted to
calibrate distorted spectral image, including Total Least Squares (TLS)
algorithm, intelligent sampling method, multi-layer feed-forward neural
networks. The calibration experiments on the LAMOST CCD images show that the
calibration effect of proposed method is effectible. At the same time, the
spectrum extraction results before and after calibration are compared, results
show the characteristics of the extracted one-dimensional waveform are more
close to an ideal optics system, and the PSF of the corrected object spectrum
image estimated by the blind deconvolution method is nearly central symmetry,
which indicates that our proposed method can significantly reduce the
complexity of spectrum extraction and improve extraction accuracy.Comment: 10 pages, 14 figure
Security of practical phase-coding quantum key distribution
Security proof of practical quantum key distribution (QKD) has attracted a
lot of attentions in recent years. Most of real-life QKD implementations are
based on phase-coding BB84 protocol, which usually uses Unbalanced Mach-Zehnder
Interferometer (UMZI) as the information coder and decoder. However, the long
arm and short arm of UMZI will introduce different loss in practical
experimental realizations, the state emitted by Alice's side is nolonger
standard BB84 states. In this paper, we will give a security analysis in this
situation. Counterintuitively, active compensation for this different loss will
only lower the secret key bit rate.Comment: 4 pages, 3 figures
Quantum Hacking on Continuous-Variable Quantum Key Distribution System using a Wavelength Attack
The security proofs of continuous-variable quantum key distribution are based
on the assumptions that the eavesdropper can neither act on the local
oscillator nor control Bob's beam splitter. These assumptions may be invalid in
practice due to potential imperfections in the implementations of such
protocols. In this paper, we consider the problem of transmitting the local
oscillator in a public channel and propose a wavelength attack which can allow
the eavesdropper to control the intensity transmission of Bob's beam splitter
by switching the wavelength of the input light. Specifically we target
continuous-variable quantum key distribution systems that use the heterodyne
detection protocol using either direct or reverse reconciliation. Our attack is
proved to be feasible and renders all of the final key shared between the
legitimate parties insecure, even if they have monitored the intensity of the
local oscillator. To prevent our attack on commercial systems, a simple
wavelength filter should be added before performing the monitoring detection.Comment: 9 pages, 4 figures. arXiv admin note: substantial text overlap with
arXiv:1206.655
Quantum key distribution based on quantum dimension and independent devices
In this paper, we propose a quantum key distribution (QKD) protocol based on
only a two-dimensional Hilbert space encoding a quantum system and independent
devices between the equipment for state preparation and measurement. Our
protocol is inspired by the fully device-independent quantum key distribution
(FDI-QKD) protocol and the measurement-device-independent quantum key
distribution (MDI-QKD) protocol. Our protocol only requires the state to be
prepared in the two dimensional Hilbert space, which weakens the state
preparation assumption in the original MDI-QKD protocol. More interestingly,
our protocol can overcome the detection loophole problem in the FDI-QKD
protocol, which greatly limits the application of FDI-QKD. Hence our protocol
can be implemented with practical optical components
Characterizing high-quality high-dimensional quantum key distribution by state mapping between different degree of freedoms
Quantum key distribution (QKD) guarantees the secure communication between
legitimate parties with quantum mechanics. High-dimensional QKD (HDQKD) not
only increases the secret key rate but also tolerates higher quantum bit error
rate (QBER). Many HDQKD experiments have been realized by utilizing
orbital-angular-momentum (OAM) photons as the degree of freedom (DOF) of OAM of
the photon is a prospective resource for HD quantum information. In this work
we proposed and characterized that a high-quality HDQKD based on
polarization-OAM hybrid states can be realized by utilizing state mapping
between different DOFs. Both the preparation and measurement procedures of the
proof-of-principle verification experiment are simple and stable. Our
experiment verified that QBER and bits
secret key rate per sifted signal can be achieved for a four-dimensional QKD
with the weak coherent light source and decoy state method.Comment: 5 figures, 2 table
Dove prism in single-path Sagnac interferometer for orbital-angular-momentum photon states
The degree of freedom of orbital angular momentum (OAM) is an important
resource in high-dimensional quantum information processing, as the quantum
number of OAM can be infinite. The Dove prism (DP) is a most common tool to
manipulate the OAM light, such as in interferometers. However, the Dove prism
does not preserve the polarization of the photon states and decreases the
sorting fidelity of the interferometer. In this work, we analyze the
polarization-dependent effect of the DP on single-path Sagnac interferometers.
The results are instructive to quantum information processing with OAM light.
We also proposed a modified single-path beam splitter Sagnac interferometer
(BSSI), of which the sorting fidelity is independent on input polarization and
can be 100\% in principle. The single-path BSSI is stable for free running.
These merits are crucial in quantum information processing, such as quantum
cryptography.Comment: 9 pages and 6 figures. To be submitted, comments are welcom
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