2,733 research outputs found
Joint analysis of TeV blazar light curves with FACT and HAWC
Probing the high energy emission processes of blazars through their
variability relies crucially on long-term monitoring. We present unprecedented
light curves from unbiased observations of very high energy fluxes from the
blazars Mrk 421 and Mrk 501 based on a joint analysis of data from the First
G-APD Cherenkov Telescope (FACT) and the High Altitude Water Cherenkov (HAWC)
Observatory. Thanks to an offset of 5.3 hours of the geographic locations, a
complementary coverage of up to 12 hours of observation per day allows us to
track variability on time scales of hours to days in more detail than with
single-instrument analyses. Complementary features, such as better sensitivity
thanks to a lower energy threshold with FACT and more regular coverage
throughout the year with HAWC, provide valuable cross checks and extensions to
the individual analyses. Daily flux comparisons for both Mrk 421 and Mrk 501
show largely correlated variations with a few significant exceptions. These
deviations between measurements can be explained through fast variability
within a few hours and will be discussed in detail.Comment: Presented at the 35th International Cosmic Ray Conference (ICRC2017),
Bexco, Busan, Korea. See arXiv:1708.02572 for all HAWC contribution
Quantum phase estimation with lossy interferometers
We give a detailed discussion of optimal quantum states for optical two-mode
interferometry in the presence of photon losses. We derive analytical formulae
for the precision of phase estimation obtainable using quantum states of light
with a definite photon number and prove that maximization of the precision is a
convex optimization problem. The corresponding optimal precision, i.e. the
lowest possible uncertainty, is shown to beat the standard quantum limit thus
outperforming classical interferometry. Furthermore, we discuss more general
inputs: states with indefinite photon number and states with photons
distributed between distinguishable time bins. We prove that neither of these
is helpful in improving phase estimation precision.Comment: 12 pages, 5 figure
Work and Quantum Phase Transitions: Is there Quantum Latency?
We study the physics of quantum phase transitions from the perspective of
non-equilibrium thermodynamics. For first order quantum phase transitions, we
find that the average work done per quench in crossing the critical point is
discontinuous. This leads us to introduce the quantum latent work in analogy
with the classical latent heat of first order classical phase transitions. For
second order quantum phase transitions the irreversible work is closely related
to the fidelity susceptibility for weak sudden quenches of the system
Hamiltonian. We demonstrate our ideas with numerical simulations of first,
second, and infinite order phase transitions in various spin chain models.Comment: accepted in PR
PYRAMIR: Calibration and operation of a pyramid near-infrared wavefront sensor
The concept of pyramid wavefront sensors (PWFS) has been around about a
decade by now. However, there is still a great lack of characterizing
measurements that allow the best operation of such a system under real life
conditions at an astronomical telescope. In this article we, therefore,
investigate the behavior and robustness of the pyramid infrared wavefront
sensor PYRAMIR mounted at the 3.5 m telescope at the Calar Alto Observatory
under the influence of different error sources both intrinsic to the sensor,
and arising in the preceding optical system. The intrinsic errors include
diffraction effects on the pyramid edges and detector read out noise. The
external imperfections consist of a Gaussian profile in the intensity
distribution in the pupil plane during calibration, the effect of an optically
resolved reference source, and noncommon-path aberrations. We investigated the
effect of three differently sized reference sources on the calibration of the
PWFS. For the noncommon-path aberrations the quality of the response of the
system is quantified in terms of modal cross talk and aliasing. We investigate
the special behavior of the system regarding tip-tilt control. From our
measurements we derive the method to optimize the calibration procedure and the
setup of a PWFS adaptive optics (AO) system. We also calculate the total
wavefront error arising from aliasing, modal cross talk, measurement error, and
fitting error in order to optimize the number of calibrated modes for on-sky
operations. These measurements result in a prediction of on-sky performance for
various conditions
Real-world Quantum Sensors: Evaluating Resources for Precision Measurement
Quantum physics holds the promise of enabling certain tasks with better
performance than possible when only classical resources are employed. The
quantum phenomena present in many experiments signify nonclassical behavior,
but do not always imply superior performance. Quantifying the enhancement
achieved from quantum behavior requires careful analysis of the resources
involved. We analyze the specific case of parameter estimation using an optical
interferometer, where increased precision can be achieved using quantum probe
states. Common performance measures are examined and it is shown that some
overestimate the improvement. For the simplest experimental case we compare the
different measures and show this overestimate explicitly. We give the preferred
analysis of real-world experiments and calculate benchmark values for
experimental parameters necessary to realize a precision enhancement.Comment: 8 pages, 3 figure
Broadband study of blazar 1ES 1959+650 during flaring state in 2016
Aim : The nearby TeV blazar 1ES 1959+650 (z=0.047) was reported to be in
flaring state during June - July 2016 by Fermi-LAT, FACT, MAGIC and VERITAS
collaborations. We studied the spectral energy distributions (SEDs) in
different states of the flare during MJD 57530 - 57589 using simultaneous
multiwaveband data to understand the possible broadband emission scenario
during the flare. Methods : The UV/optical and X-ray data from UVOT and XRT
respectively on board Swift and high energy -ray data from Fermi-LAT
are used to generate multiwaveband lightcurves as well as to obtain high flux
states and quiescent state SEDs. The correlation and lag between different
energy bands is quantified using discrete correlation function. The synchrotron
self Compton (SSC) model was used to reproduce the observed SEDs during flaring
and quiescent states of the source. Results : A decent correlation is seen
between X-ray and high energy -ray fluxes. The spectral hardening with
increase in the flux is seen in X-ray band. The powerlaw index vs flux plot in
-ray band indicates the different emission regions for 0.1 - 3 GeV and
3-300 GeV energy photons. Two zone SSC model satisfactorily fits the observed
broadband SEDs. The inner zone is mainly responsible for producing synchrotron
peak and high energy -ray part of the SED in all states. The second
zone is mainly required to produce less variable optical/UV and low energy
-ray emission. Conclusions : Conventional single zone SSC model does
not satisfactorily explain broadband emission during observation period
considered. There is an indication of two emission zones in the jet which are
responsible for producing broadband emission from optical to high energy
-rays.Comment: 11 pages, 12 figures, Accepted in A&
Entangled states of trapped ions allow measuring the magnetic field gradient of a single atomic spin
Using trapped ions in an entangled state we propose detecting a magnetic
dipole of a single atom at distance of a few m. This requires a
measurement of the magnetic field gradient at a level of about 10
Tesla/m. We discuss applications e.g. in determining a wide variation of
ionic magnetic moments, for investigating the magnetic substructure of ions
with a level structure not accessible for optical cooling and detection,and for
studying exotic or rare ions, and molecular ions. The scheme may also be used
for measureing spin imbalances of neutral atoms or atomic ensembles trapped by
optical dipole forces. As the proposed method relies on techniques well
established in ion trap quantum information processing it is within reach of
current technology.Comment: 4 pages, 2 fi
Entangling strings of neutral atoms in 1D atomic pipeline structures
We study a string of neutral atoms with nearest neighbor interaction in a 1D
beam splitter configuration, where the longitudinal motion is controlled by a
moving optical lattice potential. The dynamics of the atoms crossing the beam
splitter maps to a 1D spin model with controllable time dependent parameters,
which allows the creation of maximally entangled states of atoms by crossing a
quantum phase transition. Furthermore, we show that this system realizes
protected quantum memory, and we discuss the implementation of one- and
two-qubit gates in this setup.Comment: 4 pages, REVTEX, revised version: improvements in introduction and
figure
Quantum computations with atoms in optical lattices: marker qubits and molecular interactions
We develop a scheme for quantum computation with neutral atoms, based on the
concept of "marker" atoms, i.e., auxiliary atoms that can be efficiently
transported in state-independent periodic external traps to operate quantum
gates between physically distant qubits. This allows for relaxing a number of
experimental constraints for quantum computation with neutral atoms in
microscopic potential, including single-atom laser addressability. We discuss
the advantages of this approach in a concrete physical scenario involving
molecular interactions.Comment: 15 pages, 14 figure
Phonon Life-times from first principles self consistent lattice dynamics
Phonon lifetime calculations from first principles usually rely on time
consuming molecular dynamics calculations, or density functional perturbation
theory (DFPT) where the zero temperature crystal structure is assumed to be
dynamically stable. Here a new and effective method for calculating phonon
lifetimes from first principles is presented, not limited to crystal structures
stable at 0 K, and potentially much more effective than most corresponding
molecular dynamics calculations. The method is based on the recently developed
self consistent lattice dynamical method and is here tested by calculating the
bcc phase phonon lifetimes of Li, Na, Ti and Zr, as representative examples.Comment: 4 pages, 4 figur
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