472 research outputs found
Nonlinear optics with less than one photon
We demonstrate suppression and enhancement of spontaneous parametric down-
conversion via quantum interference with two weak fields from a local
oscillator (LO). Pairs of LO photons are observed to upconvert with high
efficiency for appropriate phase settings, exhibiting an effective nonlinearity
enhanced by at least 10 orders of magnitude. This constitutes a two-photon
switch, and promises to be useful for a variety of nonlinear optical effects at
the quantum level.Comment: 8 pages, 5 figure
Classical dispersion-cancellation interferometry
Even-order dispersion cancellation, an effect previously identified with
frequency-entangled photons, is demonstrated experimentally for the first time
with a linear, classical interferometer. A combination of a broad bandwidth
laser and a high resolution spectrometer was used to measure the intensity
correlations between anti-correlated optical frequencies. Only 14% broadening
of the correlation signal is observed when significant material dispersion,
enough to broaden the regular interferogram by 4250%, is introduced into one
arm of the interferometer.Comment: 4 pages, 3 figure
An Contribution to the Hydrogen Lamb Shift from Virtual Light by Light Scattering
The radiative correction to the Lamb shift of order
induced by the light by light scattering insertion in external photons is
obtained. The new contribution turns out to be equal to
. Combining this contribution
with our previous results we obtain the complete correction of order
induced by all diagrams with closed electron loops.
This correction is kHz and kHz for the - and
-states in hydrogen, respectively.Comment: pages, Penn State Preprint PSU/TH/142, February 199
Comment on "A linear optics implementation of weak values in Hardy's paradox"
A recent experimental proposal by Ahnert and Payne [S.E. Ahnert and M.C.
Payne, Phys. Rev. A 70, 042102 (2004)] outlines a method to measure the weak
value predictions of Aharonov in Hardy's paradox. This proposal contains flaws
such as the state preparation method and the procedure for carrying out the
requisite weak measurements. We identify previously published solutions to some
of the flaws.Comment: To be published in Physical Review
The Association Between Dental Coverage and Self-reported Health in Older Adults jGPHA
Background: For the older population of the United States, lack of dental insurance coverage is a substantial health problem. The purpose of the present study was to examine the longitudinal relationship between dental coverage and self-reported health among older adults.
Methods: The Health and Retirement Study (HRS), a nationally representative biennial cohort study of community-dwelling individuals, includes 19,595 adults (aged 50 and older) living in the United States. For the 2010, 2012, and 2014 waves, the independent variable of dental coverage and the outcome of self-reported health were examined.
Results: At each time point, dental coverage for older adults had a positive association with self-reported health (parameter estimate, β=0.340, standard error (SE)=0.039, p\u3c0.0001), controlling for sociodemographic variables of age, sex, race/ethnicity, education, and the status of edentulism. There were no significant longitudinal effects for dental coverage associated with selfreported health.
Conclusions: At each time point, the results show a positive association between having dental coverage and better self-reported health of older adults. This is relevant, because, in the United States, there is an increasing population of older people
Quantum metrology timing limits of the Hong-Ou-Mandel interferometer and of general two-photon measurements
We examine the precision limits of Hong-Ou-Mandel (HOM) timing measurements,
as well as precision limits applying to generalized two-photon measurements. As
a special case, we consider the use of two-photon measurements using photons
with variable bandwidths and frequency correlations. When the photon bandwidths
are not equal, maximizing the measurement precision involves a trade-off
between high interference visibility and strong frequency anticorrelations,
with the optimal precision occuring when the photons share non-maximal
frequency anticorrelations. We show that a generalized measurement has
precision limits that are qualitatively similar to those of the HOM measurement
whenever the generalized measurement is insensitive to the net delay of both
photons. By examining the performance of states with more general frequency
distributions, our analysis allows for engineering of the joint spectral
amplitude for use in realistic situations, in which both photons may not have
ideal spectral properties.Comment: 12 pages, 6 figures; resubmissio
Experimental joint weak measurement on a photon pair as a probe of Hardy's Paradox
It has been proposed that the ability to perform joint weak measurements on
post-selected systems would allow us to study quantum paradoxes. These
measurements can investigate the history of those particles that contribute to
the paradoxical outcome. Here, we experimentally perform weak measurements of
joint (i.e. nonlocal) observables. In an implementation of Hardy's Paradox, we
weakly measure the locations of two photons, the subject of the conflicting
statements behind the Paradox. Remarkably, the resulting weak probabilities
verify all these statements but, at the same time, resolve the Paradox
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