154 research outputs found
Reply To "Comment on 'Quantum String Seal Is Insecure' "
In Phys. Rev. A. 76, 056301 (2007), He claimed that the proof in my earlier
paper [Phys. Rev. A 75, 012327 (2007)] is insufficient to conclude the
insecurity of all quantum string seals because my measurement strategy cannot
obtain non-trivial information on the sealed string and escape detection at the
same time. Here, I clarify that our disagreement comes from our adoption of two
different criteria on the minimum amount of information a quantum string seal
can reveal to members of the public. I also point out that He did not follow my
measurement strategy correctly.Comment: 2 page
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.
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
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
On Preparing Entangled Pairs of Polarization Qubits in the Frequency Non-Degenerate Regime
The problems associated with practical implementation of the scheme proposed
for preparation of arbitrary states of polarization ququarts based on biphotons
are discussed. The influence of frequency dispersion effects are considered,
and the necessity of group velocities dispersion compensation in the frequency
non-degenerate case even for continuous pumping is demonstrated. A method for
this compensation is proposed and implemented experimentally. Physical
restrictions on the quality of prepared two-photon states are revealed.Comment: 9 pages, 6 figure
Investigaciones actuales en ligandos de receptores opiáceos
Relevant developments have been achieved in the last twenty years in the search for
opioid agonists and antagonists with selectivity for each receptor subpopulation. Recently,
new benzomorphan derivatives have been synthesized and compounds with substituted
cyclopropylmethyl functionalities at N-l position showed high affinity and selectivity for
K opioid receptor subpopulations. MPCB and CCB were selected as specific K agonists.
The affinity ofCCB was two-fold the USO,488H one. Mixed peptide-heterocyclic compounds
have been derived from these compounds and important informations on binding processes
of K ligands have been obtained.En los últimos veinte años se ha llevado a cabo una intensa investigación sobre la
búsqueda de agonistas y antagonistas selectivos de cada subtipo de receptores opiáceos.
Recientemente, se han sintetizado nuevos derivados benzomorfánicos y compuestos con
restos ciclopropilmetílicos sobre N-l que muestran alta afinidad y selectividad por los
receptores K . Los compuestos MPCB y CCB se han seleccionado como agonistas específicos K. La afinidad de CCB es dos veces mayor que la del compuesto USO,488H. De
estos compuestos se han derivado interesantes compuestos con estructura de peptidoheterocido y se han obtenido importantes informaciones sobre los procesos de binding a
los receptores K
Fidelity balance in quantum operations
I derive a tight bound between the quality of estimating the state of a
single copy of a -level system, and the degree the initial state has to be
altered in course of this procedure. This result provides a complete analytical
description of the quantum mechanical trade-off between the information gain
and the quantum state disturbance expressed in terms of mean fidelities. I also
discuss consequences of this bound for quantum teleportation using nonmaximally
entangled states.Comment: 4 pages, REVTeX. Revised versio
Triggered qutrits for Quantum Communication protocols
A general protocol in Quantum Information and Communication relies in the
ability of producing, transmitting and reconstructing, in general, qunits. In
this letter we show for the first time the experimental implementation of these
three basic steps on a pure state in a three dimensional space, by means of the
orbital angular momentum of the photons. The reconstruction of the qutrit is
performed with tomographic techniques and a Maximum-Likelihood estimation
method. In this way we also demonstrate that we can perform any transformation
in the three dimensional space
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