238 research outputs found
Experimental quantum imaging distillation with undetected light
Imaging based on the induced coherence effect makes use of photon pairs to
obtain information of an object without detecting the light that probes it.
While one photon illuminates the object, only its partner is detected, so no
measurement of coincidence events are needed. The sought-after object's
information is revealed observing a certain interference pattern on the
detected photon. Here we demonstrate experimentally that this imaging technique
can be made resilient to noise. We introduce an imaging distillation approach
based on the interferometric modulation of the signal of interest. We show that
our scheme can generate a high-quality image of an object even against noise
levels up to 250 times the actual signal of interest. We also include a
detailed theoretical explanation of our findings.Comment: 18 pages, 6 figures, and 1 table + 11 pages, 3 figures, and 1 tabl
Quantum holography with undetected light
Holography exploits the interference of light fields to obtain a systematic
reconstruction of the light fields wavefronts. Classical holography techniques
have been very successful in diverse areas such as microscopy, manufacturing
technology, and basic science. Extending holographic methods to the level of
single photons has been proven challenging, since applying classical holography
techniques to this regime pose technical problems. Recently the retrieval of
the spatial structure of a single photon, using another photon under
experimental control with a well-characterized spatial shape as reference, was
demonstrated using the intrinsically non-classical Hong-Ou-Mandel interference
on a beam splitter. Here we present a method for recording a hologram of single
photons without detecting the photons themselves, and importantly, with no need
to use a well-characterized companion reference photon. Our approach is based
on quantum interference between two-photon probability amplitudes in a
nonlinear interferometer. As in classical holography, the hologram of a single
photon allows retrieving the complete information about the "shape" of the
photon (amplitude and phase) despite the fact that the photon is never
detected.Comment: 29 pages with 11 figures, submitted to Nature Communication
Spitzer observations of NGC2264: The nature of the disk population
NGC2264 is a young cluster with a rich circumstellar disk population which
makes it an ideal target for studying the evolution of stellar clusters. Our
goal is to study its star formation history and to analyse the primordial disk
evolution of its members. The study presented is based on data obtained with
Spitzer IRAC and MIPS, combined with deep NIR ground-based FLAMINGOS imaging
and previously published optical data. We build NIR dust extinction maps of the
molecular cloud associated with the cluster, and determine it to have a mass of
2.1x10^3Msun above an Av of 7mag. Using a differential K_s-band luminosity
function of the cluster, we estimate the size of its population to be
1436242 members. The star formation efficiency is ~25%. We identify the
disk population: (i) optically thick inner disks, (ii) anaemic inner disks, and
(iii) disks with inner holes, or transition disks. We analyse the spatial
distribution of these sources and find that sources with thick disks segregate
into sub-clusterings, whereas sources with anaemic disks do not. Furthermore,
sources with anaemic disks are found to be unembedded (Av<3mag), whereas the
clustered sources with thick disks are still embedded within the parental
cloud. NGC2264 has undergone more than one star-forming event, where the
anaemic and extincted thick disk population appear to have formed in separate
episodes. We also find tentative evidence of triggered star-formation in the
Fox Fur Nebula. In terms of disk evolution, our findings support the emerging
disk evolution paradigm of two distinct evolutionary paths for primordial
optically thick disks: a homologous one where the disk emission decreases
uniformly at NIR and MIR wavelengths, and a radially differential one where the
emission from the inner region of the disk decreases more rapidly than from the
outer region (forming transition disks).Comment: accepted for publishing in A&
A Possible Detection of Occultation by a Proto-planetary Clump in GM Cephei
GM Cep in the young (~4 Myr) open cluster Trumpler 37 has been known to be an
abrupt variable and to have a circumstellar disk with very active accretion.
Our monitoring observations in 2009-2011 revealed the star to show sporadic
flare events, each with brightening of < 0.5 mag lasting for days. These
brightening events, associated with a color change toward the blue, should
originate from an increased accretion activity. Moreover, the star also
underwent a brightness drop of ~1 mag lasting for about a month, during which
the star became bluer when fainter. Such brightness drops seem to have a
recurrence time scale of a year, as evidenced in our data and the photometric
behavior of GM Cep over a century. Between consecutive drops, the star
brightened gradually by about 1 mag and became blue at peak luminosity. We
propose that the drop is caused by obscuration of the central star by an
orbiting dust concentration. The UX Orionis type of activity in GM Cep
therefore exemplifies the disk inhomogeneity process in transition between
grain coagulation and planetesimal formation in a young circumstellar disk.Comment: In submission to the Astrophysical Journal, 4 figure
Phase resolved observation of spin wave modes in antidot lattices
Antidot lattices have proven to be a powerful tool for spin wave band structure manipulation. Utilizing time-resolved scanning transmission x-ray microscopy, we are able to experimentally image edge-localized spin wave modes in an antidot lattice with a lateral confinement down to < 80 nm x 130 nm. At higher frequencies, spin wave dragonfly patterns formed by the demagnetizing structures of the antidot lattice are excited. Evaluating their relative phase with respect to the propagating mode within the antidot channel reveals that the dragonfly modes are not directly excited by the antenna but need the propagating mode as an energy mediator. Furthermore, micromagnetic simulations reveal that additional dispersion branches exist for a tilted external field geometry. These branches correspond to asymmetric spin wave modes that cannot be excited in a non-tilted field geometry due to the symmetry restriction. In addition to the band having a negative slope, these asymmetric modes also cause an unexpected transformation of the band structure, slightly reaching into the otherwise empty bandgap between the low frequency edge modes and the fundamental mode. The presented phase resolved investigation of spin waves is a crucial step for spin wave manipulation in magnonic crystals
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