838 research outputs found
Quantum cryptography with 3-state systems
We consider quantum cryptographic schemes where the carriers of information
are 3-state particles. One protocol uses four mutually unbiased bases and
appears to provide better security than obtainable with 2-state carriers.
Another possible method allows quantum states to belong to more than one basis.
The security is not better, but many curious features arise.Comment: 11 pages Revte
Quantum key distribution for d-level systems with generalized Bell states
Using the generalized Bell states and controlled not gates, we introduce an
enatanglement-based quantum key distribution (QKD) of d-level states (qudits).
In case of eavesdropping, Eve's information gain is zero and a quantum error
rate of (d-1)/d is introduced in Bob's received qudits, so that for large d,
comparison of only a tiny fraction of received qudits with the sent ones can
detect the presence of Eve.Comment: 8 pages, 3 figures, REVTEX, references added, extensive revision, to
appear in Phys. Rev.
The effectiveness of quantum operations for eavesdropping on sealed messages
A quantum protocol is described which enables a user to send sealed messages
and that allows for the detection of active eavesdroppers. We examine a class
of eavesdropping strategies, those that make use of quantum operations, and we
determine the information gain versus disturbance caused by these strategies.
We demonstrate this tradeoff with an example and we compare this protocol to
quantum key distribution, quantum direct communication, and quantum seal
protocols.Comment: 10 pages, 2 figures. Third Feynman Festival, 25 -- 29 August 2006,
University of Maryland, College Park, Maryland, U.S.
Quantum Key Distribution between N partners: optimal eavesdropping and Bell's inequalities
Quantum secret-sharing protocols involving N partners (NQSS) are key
distribution protocols in which Alice encodes her key into qubits, in
such a way that all the other partners must cooperate in order to retrieve the
key. On these protocols, several eavesdropping scenarios are possible: some
partners may want to reconstruct the key without the help of the other ones,
and consequently collaborate with an Eve that eavesdrops on the other partners'
channels. For each of these scenarios, we give the optimal individual attack
that the Eve can perform. In case of such an optimal attack, the authorized
partners have a higher information on the key than the unauthorized ones if and
only if they can violate a Bell's inequality.Comment: 14 pages, 1 figur
Orthogonality of Biphoton Polarization States
Orthogonality of two-photon polarization states belonging to a single
frequency and spatial mode is demonstrated experimentally, in a generalization
of the well-known anti-correlation 'dip' experiment.Comment: Submitted to Phys.Rev.Let
Quantum Cryptography using larger alphabets
Like all of quantum information theory, quantum cryptography is traditionally
based on two level quantum systems. In this letter, a new protocol for quantum
key distribution based on higher dimensional systems is presented. An
experimental realization using an interferometric setup is also proposed.
Analyzing this protocol from the practical side, one finds an increased key
creation rate while keeping the initial laser pulse rate constant. Analyzing it
for the case of intercept/resend eavesdropping strategy, an increased error
rate is found compared to two dimensional systems, hence an advantage for the
legitimate users to detect an eavesdropper.Comment: 12 pages, 2 (eps) figure
Mutually unbiased binary observable sets on N qubits
The Pauli operators (tensor products of Pauli matrices) provide a complete
basis of operators on the Hilbert space of N qubits. We prove that the set of
4^N-1 Pauli operators may be partitioned into 2^N+1 distinct subsets, each
consisting of 2^N-1 internally commuting observables. Furthermore, each such
partitioning defines a unique choice of 2^N+1 mutually unbiased basis sets in
the N-qubit Hilbert space. Examples for 2 and 3 qubit systems are discussed
with emphasis on the nature and amount of entanglement that occurs within these
basis sets.Comment: 5 pages, 5 figures. Replacement - expanded introduction and
conclusions; added reference
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