14,696 research outputs found
Relative intensity squeezing by four-wave mixing with loss: an analytic model and experimental diagnostic
Four-wave mixing near resonance in an atomic vapor can produce relative
intensity squeezed light suitable for precision measurements beyond the
shot-noise limit. We develop an analytic distributed gain/loss model to
describe the competition of mixing and absorption through the non-linear
medium. Using a novel matrix calculus, we present closed-form expressions for
the degree of relative intensity squeezing produced by this system. We use
these theoretical results to analyze experimentally measured squeezing from a
Rb vapor and demonstrate the analytic model's utility as an experimental
diagnostic.Comment: 10 pages, 5 figure
Grover's quantum searching algorithm is optimal
I improve the tight bound on quantum searching by Boyer et al.
(quant-ph/9605034) to a matching bound, thus showing that for any probability
of success Grovers quantum searching algorithm is optimal. E.g. for near
certain success we have to query the oracle pi/4 sqrt{N} times, where N is the
size of the search space. I also show that unfortunately quantum searching
cannot be parallelized better than by assigning different parts of the search
space to independent quantum computers. Earlier results left open the
possibility of a more efficient parallelization.Comment: 13 pages, LaTeX, essentially published versio
Blackbody Radiation and the Scaling Symmetry of Relativistic Classical Electron Theory with Classical Electromagnetic Zero-Point Radiation
It is pointed out that relativistic classical electron theory with classical
electromagnetic zero-point radiation has a scaling symmetry which is suitable
for understanding the equilibrium behavior of classical thermal radiation at a
spectrum other than the Rayleigh-Jeans spectrum. In relativistic classical
electron theory, the masses of the particles are the only scale-giving
parameters associated with mechanics while the action-angle variables are scale
invariant. The theory thus separates the interaction of the action variables of
matter and radiation from the scale-giving parameters. Classical zero-point
radiation is invariant under scattering by the charged particles of
relativistic classical electron theory. The basic ideas of the matter
-radiation interaction are illustrated in a simple relativistic classical
electromagnetic example.Comment: 18 page
Evolved stars in the Local Group galaxies. I. AGB evolution and dust production in IC 1613
We used models of thermally-pulsing asymptotic giant branch (AGB) stars, that
also describe the dust-formation process in the wind, to interpret the
combination of near- and mid-infrared photometric data of the dwarf galaxy IC
1613. This is the first time that this approach is extended to an environment
different from the Milky Way and the Magellanic Clouds (MCs). Our analysis,
based on synthetic population techniques, shows a nice agreement between the
observations and the expected distribution of stars in the colour-magnitude
diagrams obtained with JHK and Spitzer bands. This allows a characterization of
the individual stars in the AGB sample in terms of mass, chemical composition,
and formation epoch of the progenitors. We identify the stars exhibiting the
largest degree of obscuration as carbon stars evolving through the final AGB
phases, descending from 1-1.25Msun objects of metallicity Z=0.001 and from
1.5-2.5Msun stars with Z=0.002. Oxygen-rich stars constitute the majority of
the sample (65%), mainly low mass stars (<2Msun) that produce a negligible
amount of dust (<10^{-7}Msun/yr). We predict the overall dust-production rate
from IC 1613, mostly determined by carbon stars, to be 6x10^{-7}Msun/yr with an
uncertainty of 30%. The capability of the current generation of models to
interpret the AGB population in an environment different from the MCs opens the
possibility to extend this kind of analysis to other Local Group galaxies.Comment: 14 pages, 6 figures, accepted for publication on MNRA
Dust Production and Mass Loss in Cool Evolved Stars
Following the red giant branch phase and the subsequent core He-burning phase, the low- to intermediate-mass stars (0.8<M/M solar mass <8) begin to ascend the asymptotic giant branch (AGB). Pulsations levitate material from the stellar surface and provide density enhancements and shocks, which can encourage dust formation and re-processing. The dust composition depends on the atmospheric chemistry (abundance of carbon relative to oxygen), which is altered by dredging up newly formed carbon to the surface of the star. I will briefly review the current status of models that include AGB mass loss and relate them to recent observations of AGB stars from the Surveying the Agents of Galaxy Evolution (SAGE) Spitzer surveys of the Small and Large Magellanic Clouds, including measures of the total dust input to the interstellar medium from AGB stars
On the nature of the most obscured C-rich AGB stars in the Magellanic Clouds
The stars in the Magellanic Clouds with the largest degree of obscuration are
used to probe the highly uncertain physics of stars in the asymptotic giant
branch (AGB) phase of evolution. Carbon stars in particular, provide key
information on the amount of third dredge-up (TDU) and mass loss. We use two
independent stellar evolution codes to test how a different treatment of the
physics affects the evolution on the AGB. The output from the two codes are
used to determine the rates of dust formation in the circumstellar envelope,
where the method used to determine the dust is the same for each case. The
stars with the largest degree of obscuration in the LMC and SMC are identified
as the progeny of objects of initial mass and , respectively. This difference in mass is motivated by the
difference in the star formation histories of the two galaxies, and offers a
simple explanation of the redder infrared colours of C-stars in the LMC
compared to their counterparts in the SMC. The comparison with the Spitzer
colours of C-rich AGB stars in the SMC shows that a minimum surface carbon mass
fraction must have been reached by stars of initial
mass around . Our results confirm the necessity of adopting
low-temperature opacities in stellar evolutionary models of AGB stars. These
opacities allow the stars to obtain mass-loss rates high enough () to produce the amount of dust needed to reproduce the
Spitzer coloursComment: 14 pages, 5 figures, 1 table; accepted for publication in MNRAS Main
Journa
Grover's Quantum Search Algorithm for an Arbitrary Initial Mixed State
The Grover quantum search algorithm is generalized to deal with an arbitrary
mixed initial state. The probability to measure a marked state as a function of
time is calculated, and found to depend strongly on the specific initial state.
The form of the function, though, remains as it is in the case of initial pure
state. We study the role of the von Neumann entropy of the initial state, and
show that the entropy cannot be a measure for the usefulness of the algorithm.
We give few examples and show that for some extremely mixed initial states
carrying high entropy, the generalized Grover algorithm is considerably faster
than any classical algorithm.Comment: 4 pages. See http://www.cs.technion.ac.il/~danken/MSc-thesis.pdf for
extended discussio
The Large Magellanic Cloud as a laboratory for Hot Bottom Burning in massive Asymptotic Giant Branch stars
We use Spitzer observations of the rich population of Asymptotic Giant Branch
stars in the Large Magellanic Cloud (LMC) to test models describing the
internal structure and nucleosynthesis of the most massive of these stars, i.e.
those with initial mass above . To this aim, we compare
Spitzer observations of LMC stars with the theoretical tracks of Asymptotic
Giant Branch models, calculated with two of the most popular evolution codes,
that are known to differ in particular for the treatment of convection.
Although the physical evolution of the two models are significantly different,
the properties of dust formed in their winds are surprisingly similar, as is
their position in the colour-colour (CCD) and colour-magnitude (CMD) diagrams
obtained with the Spitzer bands. This model independent result allows us to
select a well defined region in the () plane,
populated by AGB stars experiencing Hot Bottom Burning, the progeny of stars
with mass . This result opens up an important test of the
strength hot bottom burning using detailed near-IR (H and K bands)
spectroscopic analysis of the oxygen-rich, high luminosity candidates found in
the well defined region of the colour-colour plane. This test is possible
because the two stellar evolution codes we use predict very different results
for the surface chemistry, and the C/O ratio in particular, owing to their
treatment of convection in the envelope and of convective boundaries during
third dredge-up. The differences in surface chemistry are most apparent when
the model stars reach the phase with the largest infrared emission.Comment: 11 pages, 14 figures, accepted for publication in MNRA
An Optical and Infrared Time-Domain Study of the Supergiant Fast X-ray Transient Candidate IC 10 X-2
We present an optical and infrared (IR) study of IC 10 X-2, a high-mass X-ray
binary in the galaxy IC 10. Previous optical and X-ray studies suggest X-2 is a
Supergiant Fast X-ray Transient: a large-amplitude (factor of 100),
short-duration (hours to weeks) X-ray outburst on 2010 May 21. We analyze R-
and g-band light curves of X-2 from the intermediate Palomar Transient Factory
taken between 2013 July 15 and 2017 Feb 14 show high-amplitude ( 1
mag), short-duration ( d) flares and dips ( 0.5 mag).
Near-IR spectroscopy of X-2 from Palomar/TripleSpec show He I,
Paschen-, and Paschen- emission lines with similar shapes and
amplitudes as those of luminous blue variables (LBVs) and LBV candidates
(LBVc). Mid-IR colors and magnitudes from Spitzer/IRAC photometry of X-2
resemble those of known LBV/LBVcs. We suggest that the stellar companion in X-2
is an LBV/LBVc and discuss possible origins of the optical flares. Dips in the
optical light curve are indicative of eclipses from optically thick clumps
formed in the winds of the stellar counterpart. Given the constraints on the
flare duration ( d) and the time between flares ( d),
we estimate the clump volume filling factor in the stellar winds, , to be
, which overlaps with values measured from massive star
winds. In X-2, we interpret the origin of the optical flares as the accretion
of clumps formed in the winds of an LBV/LBVc onto the compact object.Comment: 15 pages, 4 figures. Submitted to ApJ on Sep 26 201
Algebraic analysis of quantum search with pure and mixed states
An algebraic analysis of Grover's quantum search algorithm is presented for
the case in which the initial state is an arbitrary pure quantum state of n
qubits. This approach reveals the geometrical structure of the quantum search
process, which turns out to be confined to a four-dimensional subspace of the
Hilbert space. This work unifies and generalizes earlier results on the time
evolution of the amplitudes during the quantum search, the optimal number of
iterations and the success probability. Furthermore, it enables a direct
generalization to the case in which the initial state is a mixed state,
providing an exact formula for the success probability.Comment: 13 page
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