1,827 research outputs found
Possible cosmological implications in electrodynamics due to variations of the fine structure constant
Astronomical observations are suggesting that the fine structure constant
varies cosmologically. We present an analysis on the consequences that these
variations might induce on the electromagnetic field as a whole. We show that
under these circumstances the electrodynamics in vacuum could be described by
two fields, the ``standard'' Maxwell's field and a new scalar field. We provide
a generalised Lorentz force which can be used to test our results
experimentally.Comment: 7 pages, no figures. Accepted for publication in Rev. Mex. Fis. (Some
extra information included, references added and small corrections made to
the original version
The spectral type of CHS7797 - an intriguing very low mass periodic variable in the Orion Nebula Cluster
We present the spectroscopic characterization of the unusual high-amplitude
very low mass pre-main-sequence periodic variable CHS7797. This study is based
on optical medium-resolution (R=2200) spectroscopy in the 6450-8600 A range,
carried out with GMOS-GEMINI-S in March 2011. Observations of CHS7797 have been
carried out at two distinct phases of the 17.8d period, namely at maximum and
four days before maximum. Four different spectral indices were used for the
spectral classification at these two phases, all of them well-suited for
spectral classification of young and obscured late M dwarfs. In addition, the
gravity-sensitive NaI (8183/8195 A) and KI (7665/7699 A) doublet lines were
used to confirm the young age of CHS7797. From the spectrum obtained at maximum
light we derived a spectral type (SpT) of M6.05, while for the spectrum taken
four days before maximum the derived SpT is M5.75. The derived SpTs confirm
that CHS7797 has a mass in the stellar-substellar boundary mass range. In
addition, the small differences in the derived SpTs at the two observed phases
may provide indirect hints that CHS7797 is a binary system of similar mass
components surrounded by a tilted circumbinary disk, a system similar to KH15D.Comment: 6 pages, accepted for publication A&
Optimized generation of spatial qudits by using a pure phase spatial light modulator
We present a method for preparing arbitrary pure states of spatial qudits,
namely, D-dimensional (D > 2) quantum systems carrying information in the
transverse momentum and position of single photons. For this purpose, a set of
D slits with complex transmission are displayed on a spatial light modulator
(SLM). In a recent work we have shown a method that requires a single
phase-only SLM to control independently the complex coefficients which define
the quantum state of dimension D. The amplitude information was codified by
introducing phase gratings inside each slit and the phase value of the complex
transmission was added to the phase gratings. After a spatial filtering process
we obtained in the image plane the desired qudit state. Although this method
has proven to be a good alternative to compact the previously reported
architectures, it presents some features that could be improved. In this paper
we present an alternative scheme to codify the required phase values that
minimizes the effects of temporal phase fluctuations associated to the SLM
where the codification is carried on. In this scheme the amplitudes are set by
appropriate phase gratings addressed at the SLM while the relative phases are
obtained by a lateral displacement of these phase gratings. We show that this
method improves the quality of the prepared state and provides very high
fidelities of preparation for any state. An additional advantage of this scheme
is that a complete 2\pi modulation is obtained by shifting the grating by one
period, and hence the encoding is not limited by the phase modulation range
achieved by the SLM. Numerical simulations, that take into account the phase
fluctuations, show high fidelities for thousands of qubit states covering the
whole Bloch sphere surface. Similar analysis are performed for qudits with D =
3 and D = 7.Comment: 12 pages, 7 figure
Conditional purity and quantum correlation measures in two qubit mixed states
We analyze and show experimental results of the conditional purity, the
quantum discord and other related measures of quantum correlation in mixed
two-qubit states constructed from a pair of photons in identical polarization
states. The considered states are relevant for the description of spin pair
states in interacting spin chains in a transverse magnetic field. We derive
clean analytical expressions for the conditional local purity and other
correlation measures obtained as a result of a remote local projective
measurement, which are fully verified by the experimental results. A simple
exact expression for the quantum discord of these states in terms of the
maximum conditional purity is also derived.Comment: 16 pages, 5 figures, minor changes, to be published in J. Phys.
- …