1,367 research outputs found
Antiferromagnetism in NiO Observed by Transmission Electron Diffraction
Neutron diffraction has been used to investigate antiferromagnetism since
1949. Here we show that antiferromagnetic reflections can also be seen in
transmission electron diffraction patterns from NiO. The diffraction patterns
taken here came from regions as small as 10.5 nm and such patterns could be
used to form an image of the antiferromagnetic structure with a nanometre
resolution.Comment: 10 pages, 7 figures. Typos corrected. To appear in Physical Review
Letter
Non-classical photon pair generation in atomic vapours
A scheme for the generation of non-classical pairs of photons in atomic
vapours is proposed. The scheme exploits the fact that the cross correlation of
the emission of photons from the extreme transitions of a four-level cascade
system shows anti-bunching which has not been reported earlier and which is
unlike the case of the three level cascade emission which shows bunching. The
Cauchy-Schwarz inequality which is the ratio of cross-correlation to the auto
correlation function in this case is estimated to be for
controllable time delay, and is one to four orders of magnitude larger compared
to previous experiments. The choice of Doppler free geometry in addition to the
fact that at three photon resonance the excitation/deexcitation processes occur
in a very narrow frequency band, ensures cleaner signals.Comment: 18 pages, 7 figure
Theory and it ab initio calculation of radiative lifetime of excitons in semiconducting carbon nanotubes
We present theoretical analysis and first-principles calculation of the
radiative lifetime of excitons in semiconducting carbon nanotubes. An intrinsic
lifetime of the order of 10 ps is computed for the lowest optically active
bright excitons. The intrinsic lifetime is however a rapid increasing function
of the exciton momentum. Moreover, the electronic structure of the nanotubes
dictates the existence of dark excitons nearby in energy to each bright
exciton. Both effects strongly influence measured lifetime. Assuming a thermal
occupation of bright and dark exciton bands, we find an effective lifetime of
the order of 10 ns at room temperature, in good accord with recent experiments.Comment: 12 pages, 3 figure
Canonical, squeezed and fermionic coherent states in a right quaternionic Hilbert space with a left multiplication on it
Using a left multiplication defined on a right quaternionic Hilbert space, we
shall demonstrate that various classes of coherent states such as the canonical
coherent states, pure squeezed states, fermionic coherent states can be defined
with all the desired properties on a right quaternionic Hilbert space. Further,
we shall also demonstrate squeezed states can be defined on the same Hilbert
space, but the noncommutativity of quaternions prevents us in getting the
desired results.Comment: Conference paper. arXiv admin note: text overlap with
arXiv:1704.02946; substantial text overlap with arXiv:1706.0068
A scheme for symmetrization verification
We propose a scheme for symmetrization verification in two-particle systems,
based on one-particle detection and state determination. In contrast to
previous proposals, it does not follow a Hong-Ou-Mandel-type approach.
Moreover, the technique can be used to generate superposition states of single
particles
All-Optical Switching Using the Quantum Zeno Effect and Two-Photon Absorption
We have previously shown that the quantum Zeno effect can be used to
implement quantum logic gates for quantum computing applications, where the
Zeno effect was produced using a strong two-photon absorbing medium. Here we
show that the Zeno effect can also be used to implement classical logic gates
whose inputs and outputs are high-intensity fields (coherent states). The
operation of the devices can be understood using a quasi-static analysis, and
their switching times are calculated using a dynamic approach. The two-photon
absorption coefficient of rubidium vapor is shown to allow operation of these
devices at relatively low power levels.Comment: 21 pages, 11 figures. Submitted to Phys. Rev.
Permutation asymmetry inducing entanglement between degrees of freedom in multiphoton states
We describe and examine entanglement between different degrees of freedom in
multiphoton states based on the permutation properties. From the state
description, the entanglement comes from the permutation asymmetry. According
to the different permutation properties, the multiphoton states can be divided
into several parts. It will help to deal with the multiphoton interference,
which can be used as the measurement of the entanglement.Comment: Final versio
Contraception
“ Every Child a Wanted Child” — this was the stated ambition of a campaign launched by the Family Planning Association in June, 1969. Few enlightened people would disagree with this ideal, yet the majority give little thought as to how it can be achieved and most are quite unaware of how difficult it is for women, especially among the lower social groups, to obtain advice on contraception. Millions of pounds are spent each year in anattempt to stop the world population explosion, but in Great Britain, one of the most densely populated countries in the world and one which boasts of its Welfare Services, free Family Planning advice is available to only a small percentage of women. It is estimated that in Scotland as few as 25-35% of pregnancies are planned. One in three of babies born to mothers under the age of 20 are conceived before marriage. The illegitimacy rate is rising steadily. Add to these the number of abortions which are induced therapeutically or illegally each year and a dismal picture of unplanned pregnancy emerges
A molecular theory for two-photon and three-photon fluorescence polarization
In the analysis of molecular structure and local order in heterogeneous samples, multiphoton excitation of fluorescence affords chemically specific information and high-resolution imaging. This report presents the results of an investigation that secures a detailed theoretical representation of the fluorescence polarization produced by one-, two-, and three-photon excitations, with orientational averaging procedures being deployed to deliver the fully disordered limits. The equations determining multiphoton fluorescence response prove to be expressible in a relatively simple, generic form, and graphs exhibit the functional form of the multiphoton fluorescence polarization. Amongst other features, the results lead to the identification of a condition under which the fluorescence produced through the concerted absorption of any number of photons becomes completely unpolarized. It is also shown that the angular variation of fluorescence intensities is reliable indicator of orientational disorder
Nonlinear Interferometry via Fock State Projection
We use a photon-number resolving detector to monitor the photon number
distribution of the output of an interferometer, as a function of phase delay.
As inputs we use coherent states with mean photon number up to seven. The
postselection of a specific Fock (photon-number) state effectively induces
high-order optical non-linearities. Following a scheme by Bentley and Boyd
[S.J. Bentley and R.W. Boyd, Optics Express 12, 5735 (2004)] we explore this
effect to demonstrate interference patterns a factor of five smaller than the
Rayleigh limit.Comment: 4 pages, 5 figure
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