37,489 research outputs found
High-dimensional quantum cryptography with twisted light
Quantum key distributions (QKD) systems often rely on polarization of light
for encoding, thus limiting the amount of information that can be sent per
photon and placing tight bounds on the error that such a system can tolerate.
Here we describe a proof-of-principle experiment that indicates the feasibility
of high-dimensional QKD based on the transverse structure of the light field,
allowing for the transfer of more than 1 bit per photon. Our implementation
uses the orbital angular momentum (OAM) of photons and the corresponding
mutually unbiased basis of angular position (ANG). Our experiment uses a
digital micro-mirror device for the rapid generation of OAM and ANG modes at 4
kHz, and a mode sorter capable of sorting single photons based on their OAM and
ANG content with a separation efficiency of 93\%. Through the use of a
7-dimensional alphabet encoded in the OAM and ANG bases, we achieve a channel
capacity of 2.05 bits per sifted photon. Our experiment shows that, in addition
to having an increased information capacity, QKD systems based on spatial-mode
encoding will be more tolerant to errors and thus more robust against
eavesdropping attacks
Practical quantum key distribution over a 48-km optical fiber network
The secure distribution of the secret random bit sequences known as "key"
material, is an essential precursor to their use for the encryption and
decryption of confidential communications. Quantum cryptography is a new
technique for secure key distribution with single-photon transmissions:
Heisenberg's uncertainty principle ensures that an adversary can neither
successfully tap the key transmissions, nor evade detection (eavesdropping
raises the key error rate above a threshold value). We have developed
experimental quantum cryptography systems based on the transmission of
non-orthogonal photon states to generate shared key material over
multi-kilometer optical fiber paths and over line-of-sight links. In both
cases, key material is built up using the transmission of a single-photon per
bit of an initial secret random sequence. A quantum-mechanically random subset
of this sequence is identified, becoming the key material after a data
reconciliation stage with the sender. Here we report the most recent results of
our optical fiber experiment in which we have performed quantum key
distribution over a 48-km optical fiber network at Los Alamos using photon
interference states with the B92 and BB84 quantum key distribution protocols.Comment: 13 pages, 7 figures, .pdf format submitted to Journal of Modern
Optic
Quantum e-commerce: A comparative study of possible protocols for online shopping and other tasks related to e-commerce
A set of quantum protocols for online shopping is proposed and analyzed to
establish that it is possible to perform secure online shopping using different
types of quantum resources. Specifically, a single photon based, a Bell state
based and two 3-qubit entangled state based quantum online shopping schemes are
proposed. The Bell state based scheme, being a completely orthogonal state
based protocol, is fundamentally different from the earlier proposed schemes
which were based on conjugate coding. One of the 3-qubit entangled state based
scheme is build on the principle of entanglement swapping which enables us to
accomplish the task without transmission of the message encoded qubits through
the channel. Possible ways of generalizing the entangled state based schemes
proposed here to the schemes which use multiqubit entangled states is also
discussed. Further, all the proposed protocols are shown to be free from the
limitations of the recently proposed protocol of Huang et al. (Quantum Inf.
Process. 14, 2211-2225, 2015) which allows the buyer (Alice) to change her
order at a later time (after initially placing the order and getting it
authenticated by the controller). The proposed schemes are also compared with
the existing schemes using qubit efficiency.Comment: It's shown that quantum e-commerce is not a difficult task, and it
can be done in various way
A general scheme for information interception in the ping pong protocol
The existence of an undetectable eavesdropping of dense coded information has
been already demonstrated by Pavi\v{c}i\'c for the quantum direct communication
based on the ping-pong paradigm. However, a) the explicit scheme of the circuit
is only given and no design rules are provided, b) the existence of losses is
implicitly assumed, c) the attack has been formulated against qubit based
protocol only and it is not clear whether it can be adapted to higher
dimensional systems. These deficiencies are removed in the presented
contribution. A new generic eavesdropping scheme built on a firm theoretical
background is proposed. In contrast to the previous approach, it does not refer
to the properties of the vacuum state, so it is fully consistent with the
absence of losses assumption. Moreover, the scheme applies to the communication
paradigm based on signal particles of any dimensionality. It is also shown that
some well known attacks are special cases of the proposed scheme.Comment: 10 pages, 4 figure
Quantum Cryptography Beyond Quantum Key Distribution
Quantum cryptography is the art and science of exploiting quantum mechanical
effects in order to perform cryptographic tasks. While the most well-known
example of this discipline is quantum key distribution (QKD), there exist many
other applications such as quantum money, randomness generation, secure two-
and multi-party computation and delegated quantum computation. Quantum
cryptography also studies the limitations and challenges resulting from quantum
adversaries---including the impossibility of quantum bit commitment, the
difficulty of quantum rewinding and the definition of quantum security models
for classical primitives. In this review article, aimed primarily at
cryptographers unfamiliar with the quantum world, we survey the area of
theoretical quantum cryptography, with an emphasis on the constructions and
limitations beyond the realm of QKD.Comment: 45 pages, over 245 reference
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