1,394 research outputs found
Sundays in a Quantum Engineer's Life
I am a Quantum Engineer, but on Sundays I have principles, John Bell opened
his "underground colloquium" in March 1983, words which I will never forget!
What! John Bell, the great John Bell, presented himself as an engineer!?! one
of those people who make things work without even understanding how they
function?!? whereas I thought of John Bell as one of the greatest theoretician.Comment: Talk presented at the Conference in Commemoration of John S. Bell,
Vienna 10-14 November 2000. 4 pages & 3 figure
Quantum Cloning, Eavesdropping and Bell's inequality
We analyze various eavesdropping strategies on a quantum cryptographic
channel. We present the optimal strategy for an eavesdropper restricted to a
two-dimensional probe, interacting on-line with each transmitted signal. The
link between safety of the transmission and the violation of Bell's inequality
is discussed. We also use a quantum copying machine for eavesdropping and for
broadcasting quantum information.Comment: LaTex, 13 pages, with 6 Postscript figure
Quantum Relative States
We study quantum state estimation problems where the reference system with
respect to which the state is measured should itself be treated quantum
mechanically. In this situation, the difference between the system and the
reference tends to fade. We investigate how the overlap between two pure
quantum states can be optimally estimated, in several scenarios, and we
re-visit homodyne detection.Comment: 10 page
EPR Test with Photons and Kaons: Analogies
We present a unified formalism describing EPR test using spin 1/2 particles,
photons and kaons. This facilitates the comparison between existing experiments
using photons and kaons. It underlines the similarities between birefringence
and polarization dependent losses that affects experiments using optical fibers
and mixing and decay that are intrinsic to the kaons. We also discuss the
limitation these two characteristics impose on the testing of Bell's
inequality.Comment: 12 pages, 5 figure
Linking Measures for Macroscopic Quantum States via Photon-Spin Mapping
We review and compare several measures that identify quantum states that are
"macroscopically quantum". These measures were initially formulated either for
photonic systems or spin ensembles. Here, we compare them through a simple
model which maps photonic states to spin ensembles. On the one hand, we reveal
problems for some spin measures to handle correctly photonic states that
typically are considered to be macroscopically quantum. On the other hand, we
find significant similarities between other measures even though they were
differently motivated.Comment: 12 pages, 1 figure; published in a special issue of Optics
Communications: "Macroscopic quantumness: theory and applications in optical
sciences"; v2: minor change
Coherent quantum measurement for the direct determination of the degree of polarization and Polarization Mode Dispersion compensation
An example of a coherent measurement for the direct evaluation of the degree
of polarization of a single-mode optical beam is presented. It is applied to
the case of great practical importance where depolarization is caused by
polarization mode dispersion. It is demonstrated that coherent measurement has
the potential of significantly increasing the information gain, compared to
standard incoherent measurements.Comment: 4 pages + 3 figure
Nonlinear quantum state transformation of spin-1/2
A non-linear quantum state transformation is presented. The transformation,
which operates on pairs of spin-1/2, can be used to distinguish optimally
between two non-orthogonal states. Similar transformations applied locally on
each component of an entangled pair of spin-1/2 can be used to transform a
mixed nonlocal state into a quasi-pure maximally entangled singlet state. In
both cases the transformation makes use of the basic building block of the
quantum computer, namely the quantum-XOR gate.Comment: 12 pages, LaTeX, amssym, epsfig (2 figures included
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