291 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
Entangled-State Lithography: Tailoring any Pattern with a Single State
We demonstrate a systematic approach to Heisenberg-limited lithographic image
formation using four-mode reciprocal binominal states. By controlling the
exposure pattern with a simple bank of birefringent plates, any pixel pattern
on a grid, occupying a square with the side half a
wavelength long, can be generated from a -photon state.Comment: 4 pages, 4 figure
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
Sub-wavelength lithography over extended areas
We demonstrate a systematic approach to sub-wavelength resolution
lithographic image formation on films covering areas larger than a wavelength
squared. For example, it is possible to make a lithographic pattern with a
feature size resolution of by using a particular -photon, multi-mode entangled state, where , and banks of birefringent
plates. By preparing a statistically mixed such a state one can form any pixel
pattern on a pixel grid occupying a square
with a side of wavelengths. Hence, there is a trade-off between
the exposed area, the minimum lithographic feature size resolution, and the
number of photons used for the exposure. We also show that the proposed method
will work even under non-ideal conditions, albeit with somewhat poorer
performance.Comment: 8 pages, 8 figures, 1 table. Written in 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
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
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
Translocation of Crohn's disease Escherichia coli across M-cells: contrasting effects of soluble plant fibres and emulsifiers
Background Crohns disease is common in developed nations where the typical diet is low in fibre and high in processed food. Primary lesions overlie Peyers patches and colonic lymphoid follicles where bacterial invasion through M-cells occurs. We have assessed the effect of soluble non-starch polysaccharide (NSP) and food emulsifiers on translocation of Escherichia coli across M-cells. Methods To assess effects of soluble plant fibres and food emulsifiers on translocation of mucosa-associated E coli isolates from Crohns disease patients and from non-Crohns controls, we used M-cell monolayers, generated by co-culture of Caco2-cl1 and Raji B cells, and human Peyers patches mounted in Ussing chambers. Results E coli translocation increased across M-cells compared to parent Caco2-cl1 monocultures; 15.8-fold (IQR 6.2-32.0) for Crohns disease E coli (N=8) and 6.7-fold (IQR 3.7-21.0) for control isolates (N=5). Electronmicroscopy confirmed E coli within M-cells. Plantain and broccoli NSP markedly reduced E coli translocation across M-cells at 5 mg/ml (range 45.3-82.6% inhibition, pandlt;0.01); apple and leek NSP had no significant effect. Polysorbate-80, 0.01% vol/vol, increased E coli translocation through Caco2-cl1 monolayers 59-fold (pandlt;0.05) and, at higher concentrations, increased translocation across M-cells. Similarly, E coli translocation across human Peyers patches was reduced 45+/-7% by soluble plantain NSP (5 mg/ml) and increased 2-fold by polysorbate-80 (0.1% vol/vol). Conclusions Translocation of E coli across M-cells is reduced by soluble plant fibres, particularly plantain and broccoli, but increased by the emulsifier Polysorbate-80. These effects occur at relevant concentrations and may contribute to the impact of dietary factors on Crohns disease pathogenesis
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