2,775 research outputs found
Decoy state quantum key distribution with two-way classical post-processing
Decoy states have recently been proposed as a useful method for substantially
improving the performance of quantum key distribution protocols when a coherent
state source is used. Previously, data post-processing schemes based on one-way
classical communications were considered for use with decoy states. In this
paper, we develop two data post-processing schemes for the decoy-state method
using two-way classical communications. Our numerical simulation (using
parameters from a specific QKD experiment as an example) results show that our
scheme is able to extend the maximal secure distance from 142km (using only
one-way classical communications with decoy states) to 181km. The second scheme
is able to achieve a 10% greater key generation rate in the whole regime of
distances
Deterministic secure quantum communication with and without entanglement
We present a protocol for sending a message over a quantum channel with
different layers of security that will prevent an eavesdropper from deciphering
the message without being detected. The protocol has two versions where the
bits are encoded in either pairs of entangled photons or separate photons.
Unlike many other protocols, it requires a one-way, rather than a two-way,
quantum channel and does not require a quantum memor. A quantum key is used to
encrypt the message and both the key and the message are sent over the quantum
channle with the same quantum encoding technique. The key is sent only if no
eavesdropper is detected.Comment: 9 pages, 3 figures. Major changes in section 3 and 4. Accepted for
publication in Physica Script
Unconditional security at a low cost
By simulating four quantum key distribution (QKD) experiments and analyzing
one decoy-state QKD experiment, we compare two data post-processing schemes
based on security against individual attack by L\"{u}tkenhaus, and
unconditional security analysis by Gottesman-Lo-L\"{u}tkenhaus-Preskill. Our
results show that these two schemes yield close performances. Since the Holy
Grail of QKD is its unconditional security, we conclude that one is better off
considering unconditional security, rather than restricting to individual
attacks.Comment: Accepted by International Conference on Quantum Foundation and
Technology: Frontier and Future 2006 (ICQFT'06
The quantum cryptographic switch
We illustrate using a quantum system the principle of a cryptographic switch,
in which a third party (Charlie) can control to a continuously varying degree
the amount of information the receiver (Bob) receives, after the sender (Alice)
has sent her information. Suppose Charlie transmits a Bell state to Alice and
Bob. Alice uses dense coding to transmit two bits to Bob. Only if the 2-bit
information corresponding to choice of Bell state is made available by Charlie
to Bob can the latter recover Alice's information. By varying the information
he gives, Charlie can continuously vary the information recovered by Bob. The
performance of the protocol subjected to the squeezed generalized amplitude
damping channel is considered. We also present a number of practical situations
where a cryptographic switch would be of use.Comment: 7 pages, 4 Figure
Two-step orthogonal-state-based protocol of quantum secure direct communication with the help of order-rearrangement technique
The Goldenberg-Vaidman (GV) protocol for quantum key distribution (QKD) uses
orthogonal encoding states of a particle. Its security arises because
operations accessible to Eve are insufficient to distinguish the two states
encoding the secret bit. We propose a two-particle cryptographic protocol for
quantum secure direct communication, wherein orthogonal states encode the
secret, and security arises from restricting Eve from accessing any
two-particle operations. However, there is a non-trivial difference between the
two cases. While the encoding states are perfectly indistinguishable in GV,
they are partially distinguishable in the bi-partite case, leading to a
qualitatively different kind of information-vs-disturbance trade-off and also
options for Eve in the two cases.Comment: 9 pages, 4 figures, LaTex, Accepted for publication in Quantum
Information Processing (2014
Free-space quantum key distribution by rotation-invariant twisted photons
Twisted photons are photons carrying a well-defined nonzero value of orbital
angular momentum (OAM). The associated optical wave exhibits a helical shape of
the wavefront (hence the name) and an optical vortex at the beam axis. The OAM
of light is attracting a growing interest for its potential in photonic
applications ranging from particle manipulation, microscopy and
nanotechnologies, to fundamental tests of quantum mechanics, classical data
multiplexing and quantum communication. Hitherto, however, all results obtained
with optical OAM were limited to laboratory scale. Here we report the
experimental demonstration of a link for free-space quantum communication with
OAM operating over a distance of 210 meters. Our method exploits OAM in
combination with optical polarization to encode the information in
rotation-invariant photonic states, so as to guarantee full independence of the
communication from the local reference frames of the transmitting and receiving
units. In particular, we implement quantum key distribution (QKD), a protocol
exploiting the features of quantum mechanics to guarantee unconditional
security in cryptographic communication, demonstrating error-rate performances
that are fully compatible with real-world application requirements. Our results
extend previous achievements of OAM-based quantum communication by over two
orders of magnitudes in the link scale, providing an important step forward in
achieving the vision of a worldwide quantum network
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