226 research outputs found
Assessing the Polarization of a Quantum Field from Stokes Fluctuation
We propose an operational degree of polarization in terms of the variance of
the projected Stokes vector minimized over all the directions of the Poincar\'e
sphere. We examine the properties of this degree and show that some problems
associated with the standard definition are avoided. The new degree of
polarization is experimentally determined using two examples: a bright squeezed
state and a quadrature squeezed vacuum.Comment: 4 pages, 2 figures. Comments welcome
Quantum degrees of polarization
We discuss different proposals for the degree of polarization of quantum
fields. The simplest approach, namely making a direct analogy with the
classical description via the Stokes operators, is known to produce
unsatisfactory results. Still, we argue that these operators and their
properties should be basic for any measure of polarization. We compare
alternative quantum degrees and put forth that they order various states
differently. This is to be expected, since, despite being rooted in the Stokes
operators, each of these measures only captures certain characteristics.
Therefore, it is likely that several quantum degrees of polarization will
coexist, each one having its specific domain of usefulness.Comment: 9 pages, 3 figures. v2: Minor corrections and improvement
Two-photon imaging and quantum holography
It has been claimed that ``the use of entangled photons in an imaging system
can exhibit effects that cannot be mimicked by any other two-photon source,
whatever strength of the correlations between the two photons'' [A. F.
Abouraddy, B. E. A. Saleh, A. V. Sergienko, and M. C. Teich, Phys. Rev. Lett.
87, 123602 (2001)]. While we believe that the cited statement is true, we show
that the method proposed in that paper, with ``bucket detection'' of one of the
photons, will give identical results for entangled states as for appropriately
prepared classically correlated states.Comment: 4 pages, 2 figures, REVTe
Distance-based degrees of polarization for a quantum field
It is well established that unpolarized light is invariant with respect to
any SU(2) polarization transformation. This requirement fully characterizes the
set of density matrices representing unpolarized states. We introduce the
degree of polarization of a quantum state as its distance to the set of
unpolarized states. We use two different candidates of distance, namely the
Hilbert-Schmidt and the Bures metric, showing that they induce fundamentally
different degrees of polarization. We apply these notions to relevant field
states and we demonstrate that they avoid some of the problems arising with the
classical definition.Comment: 8 pages, 1 eps figur
Simultaneous minimum-uncertainty measurement of discrete-valued complementary observables
We have made the first experimental demonstration of the simultaneous minimum
uncertainty product between two complementary observables for a two-state
system (a qubit). A partially entangled two-photon state was used to perform
such measurements. Each of the photons carries (partial) information of the
initial state thus leaving a room for measurements of two complementary
observables on every member in an ensemble.Comment: 4 pages, 4 figures, REVTeX, submitted to PR
Maximally polarized states for quantum light fields
The degree of polarization of a quantum state can be defined as its
Hilbert-Schmidt distance to the set of unpolarized states. We demonstrate that
the states optimizing this degree for a fixed average number of photons
present a fairly symmetric, parabolic photon statistics, with a
variance scaling as . Although no standard optical process yields
such a statistics, we show that, to an excellent approximation, a highly
squeezed vacuum can be considered as maximally polarized.Comment: 4 pages, 3 eps-color figure
Surface characterization and surface electronic structure of organic quasi-one-dimensional charge transfer salts
We have thoroughly characterized the surfaces of the organic charge-transfer
salts TTF-TCNQ and (TMTSF)2PF6 which are generally acknowledged as prototypical
examples of one-dimensional conductors. In particular x-ray induced
photoemission spectroscopy turns out to be a valuable non-destructive
diagnostic tool. We show that the observation of generic one-dimensional
signatures in photoemission spectra of the valence band close to the Fermi
level can be strongly affected by surface effects. Especially, great care must
be exercised taking evidence for an unusual one-dimensional many-body state
exclusively from the observation of a pseudogap.Comment: 11 pages, 12 figures, v2: minor changes in text and figure labellin
Central-moment description of polarization for quantum states of light
We present a moment expansion method for the systematic characterization of
the polarization properties of quantum states of light. Specifically, we link
the method to the measurements of the Stokes operator in different directions
on the Poincar\'{e} sphere, and provide a method of polarization tomography
without resorting to full state tomography. We apply these ideas to the
experimental first- and second-order polarization characterization of some
two-photon quantum states. In addition, we show that there are classes of
states whose polarization characteristics are dominated not by their
first-order moments (i.e., the Stokes vector) but by higher-order polarization
moments.Comment: 11 pages, 7 figures, 4 tables, In version 2, Figs. 2 and 4 are
replaced, Sec. IV extended, Sec. VIII revised, a few references adde
Approaching the Heisenberg limit with two mode squeezed states
Two mode squeezed states can be used to achieve Heisenberg limit scaling in
interferometry: a phase shift of can be
resolved. The proposed scheme relies on balanced homodyne detection and can be
implemented with current technology. The most important experimental
imperfections are studied and their impact quantified.Comment: 4 pages, 7 figure
Complementarity and the uncertainty relations
We formulate a general complementarity relation starting from any Hermitian
operator with discrete non-degenerate eigenvalues. We then elucidate the
relationship between quantum complementarity and the Heisenberg-Robertson's
uncertainty relation. We show that they are intimately connected. Finally we
exemplify the general theory with some specific suggested experiments.Comment: 9 pages, 4 figures, REVTeX, uses epsf.sty and multicol.st
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