37,099 research outputs found
Quantum Key Distribution over Probabilistic Quantum Repeaters
A feasible route towards implementing long-distance quantum key distribution
(QKD) systems relies on probabilistic schemes for entanglement distribution and
swapping as proposed in the work of Duan, Lukin, Cirac, and Zoller (DLCZ)
[Nature 414, 413 (2001)]. Here, we calculate the conditional throughput and
fidelity of entanglement for DLCZ quantum repeaters, by accounting for the DLCZ
self-purification property, in the presence of multiple excitations in the
ensemble memories as well as loss and other sources of inefficiency in the
channel and measurement modules. We then use our results to find the generation
rate of secure key bits for QKD systems that rely on DLCZ quantum repeaters. We
compare the key generation rate per logical memory employed in the two cases of
with and without a repeater node. We find the cross-over distance beyond which
the repeater system outperforms the non-repeater one. That provides us with the
optimum inter-node distancing in quantum repeater systems. We also find the
optimal excitation probability at which the QKD rate peaks. Such an optimum
probability, in most regimes of interest, is insensitive to the total distance.Comment: 12 pages, 6 figures; Fig. 5(a) is replace
Quantum adaptation of noisy channels
Probabilistic quantum filtering is proposed to properly adapt sequential
independent quantum channels in order to stop sudden death of entanglement. In
the adaptation, the quantum filtering does not distill or purify more
entanglement, it rather properly prepares entangled state to the subsequent
quantum channel. For example, the quantum adaptation probabilistically
eliminates the sudden death of entanglement of two-qubit entangled state with
isotropic noise injected into separate amplitude damping channels. The result
has a direct application in quantum key distribution through noisy channels.Comment: 6 pages, 4 figure
Analysis of the Security of BB84 by Model Checking
Quantum Cryptography or Quantum key distribution (QKD) is a technique that
allows the secure distribution of a bit string, used as key in cryptographic
protocols. When it was noted that quantum computers could break public key
cryptosystems based on number theory extensive studies have been undertaken on
QKD. Based on quantum mechanics, QKD offers unconditionally secure
communication. Now, the progress of research in this field allows the
anticipation of QKD to be available outside of laboratories within the next few
years. Efforts are made to improve the performance and reliability of the
implemented technologies. But several challenges remain despite this big
progress. The task of how to test the apparatuses of QKD For example did not
yet receive enough attention. These devises become complex and demand a big
verification effort. In this paper we are interested in an approach based on
the technique of probabilistic model checking for studying quantum information.
Precisely, we use the PRISM tool to analyze the security of BB84 protocol and
we are focused on the specific security property of eavesdropping detection. We
show that this property is affected by the parameters of quantum channel and
the power of eavesdropper.Comment: 12 Pages, IJNS
Entanglement generation in a quantum network at distance-independent rate
We develop a protocol for entanglement generation in the quantum internet
that allows a repeater node to use -qubit Greenberger-Horne-Zeilinger (GHZ)
projective measurements that can fuse successfully-entangled {\em links},
i.e., two-qubit entangled Bell pairs shared across network edges, incident
at that node. Implementing -fusion, for , is in principle not much
harder than -fusions (Bell-basis measurements) in solid-state qubit
memories. If we allow even -fusions at the nodes, we find---by developing a
connection to a modified version of the site-bond percolation problem---that
despite lossy (hence probabilistic) link-level entanglement generation, and
probabilistic success of the fusion measurements at nodes, one can generate
entanglement between end parties Alice and Bob at a rate that stays constant as
the distance between them increases. We prove that this powerful network
property is not possible to attain with any quantum networking protocol built
with Bell measurements and multiplexing alone. We also design a two-party
quantum key distribution protocol that converts the entangled states shared
between two nodes into a shared secret, at a key generation rate that is
independent of the distance between the two parties
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