1,880 research outputs found
Experimental Study of the Quantum States of Light and Realization of a Quantum Communication Protocol\ud
I present how to obtain and characterize quantum states of light potentially useful for quantum communication protocols. The control of the frequency correlations,\ud
and the bandwidth, of single and paired photons is an essential ingredient in specific quantum applications, from quantum imaging to quantum clock synchronization.\ud
I show both theoretical and experimental spectral correlations of pairs of photons generated in non-collinear spontaneous parametric down conversion (SPDC). In the second part of the work, a scheme for quantum key distribution using the two-way LM05 protocol [PRL 94, 140501 (2005)] and its implementation is presented too. A preliminary transmission test is discussed together with\ud
an experimental study for the security of the generated key in presence of noise in the channels. The noise is modulated as to simulate the effect of an eavesdropper.\u
Quantum versus classical domains for teleportation with continuous variables
By considering the utilization of a classical channel without quantum entanglement, fidelity Fclassical=1/2 has been established as setting the boundary between classical and quantum domains in the teleportation of coherent states of the electromagnetic field [S. L. Braunstein, C. A. Fuchs, and H. J. Kimble, J. Mod. Opt. 47, 267 (2000)]. We further examine the quantum-classical boundary by investigating questions of entanglement and Bell-inequality violations for the Einstein-Podolsky-Rosen states relevant to continuous variable teleportation. The threshold fidelity for employing entanglement as a quantum resource in teleportation of coherent states is again found to be Fclassical=1/2. Likewise, violations of local realism onset at this same threshold, with the added requirement of overall efficiency η>2/3 in the unconditional case. By contrast, recently proposed criteria adapted from the literature on quantum-nondemolition detection are shown to be largely unrelated to the questions of entanglement and Bell-inequality violations
From "Dirac combs" to Fourier-positivity
Motivated by various problems in physics and applied mathematics, we look for
constraints and properties of real Fourier-positive functions, i.e. with
positive Fourier transforms. Properties of the "Dirac comb" distribution and of
its tensor products in higher dimensions lead to Poisson resummation, allowing
for a useful approximation formula of a Fourier transform in terms of a limited
number of terms. A connection with the Bochner theorem on positive definiteness
of Fourier-positive functions is discussed. As a practical application, we find
simple and rapid analytic algorithms for checking Fourier-positivity in 1- and
(radial) 2-dimensions among a large variety of real positive functions. This
may provide a step towards a classification of positive positive-definite
functions.Comment: 17 pages, 14 eps figures (overall 8 figures in the text
The String Tension in Gauge Theories
A review article on string tension concept and their relevance as
non-perturbative quantity on the study of quark confinement in lattice gauge
theories. A detailed description of a variety of methods to measure the string
tension on the lattice and an indication of the most promising developments is
proposed.Comment: Postscript file, 46 pages and 14 figure
Assumptions in Quantum Cryptography
Quantum cryptography uses techniques and ideas from physics and computer
science. The combination of these ideas makes the security proofs of quantum
cryptography a complicated task. To prove that a quantum-cryptography protocol
is secure, assumptions are made about the protocol and its devices. If these
assumptions are not justified in an implementation then an eavesdropper may
break the security of the protocol. Therefore, security is crucially dependent
on which assumptions are made and how justified the assumptions are in an
implementation of the protocol.
This thesis is primarily a review that analyzes and clarifies the connection
between the security proofs of quantum-cryptography protocols and their
experimental implementations. In particular, we focus on quantum key
distribution: the task of distributing a secret random key between two parties.
We provide a comprehensive introduction to several concepts: quantum mechanics
using the density operator formalism, quantum cryptography, and quantum key
distribution. We define security for quantum key distribution and outline
several mathematical techniques that can either be used to prove security or
simplify security proofs. In addition, we analyze the assumptions made in
quantum cryptography and how they may or may not be justified in
implementations.
Along with the review, we propose a framework that decomposes
quantum-key-distribution protocols and their assumptions into several classes.
Protocol classes can be used to clarify which proof techniques apply to which
kinds of protocols. Assumption classes can be used to specify which assumptions
are justified in implementations and which could be exploited by an
eavesdropper. Two contributions of the author are discussed: the security
proofs of two two-way quantum-key-distribution protocols and an intuitive proof
of the data-processing inequality.Comment: PhD Thesis, 221 page
Event program
UNLV Undergraduates from all departments, programs and colleges participated in a campus-wide symposium on April 16, 2011. Undergraduate posters from all disciplines and also oral presentations of research activities, readings and other creative endeavors were exhibited throughout the festival
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