9,815 research outputs found
Momentum dependent ultrafast electron dynamics in antiferromagnetic EuFe2As2
Employing the momentum-sensitivity of time- and angle-resolved photoemission
spectroscopy we demonstrate the analysis of ultrafast single- and many-particle
dynamics in antiferromagnetic EuFe2As2. Their separation is based on a
temperature-dependent difference of photo-excited hole and electron relaxation
times probing the single particle band and the spin density wave gap,
respectively. Reformation of the magnetic order occurs at 800 fs, which is four
times slower compared to electron-phonon equilibration due to a smaller
spin-dependent relaxation phase space
Towards efficient calibration for webcam eye-tracking in online experiments
Calibration is performed in eye-tracking studies to map raw model outputs to gaze-points on the screen and improve accuracy of gaze predictions. Calibration parameters, such as user-screen distance, camera intrinsic properties, and position of the screen with respect to the camera can be easily calculated in controlled offline setups, however, their estimation is non-trivial in unrestricted, online, experimental settings. Here, we propose the application of deep learning models for eye-tracking in online experiments, providing suitable strategies to estimate calibration parameters and perform personal gaze calibration. Focusing on fixation accuracy, we compare results with respect to calibration frequency, the time point of calibration during data collection (beginning, middle, end), and calibration procedure (fixation-point or smooth pursuit-based). Calibration using fixation and smooth pursuit tasks, pooled over three collection time-points, resulted in the best fixation accuracy. By combining device calibration, gaze calibration, and the best-performing deep-learning model, we achieve an accuracy of 2.580−a considerable improvement over reported accuracies in previous online eye-tracking studies
Electron-phonon coupling in 122 Fe pnictides analyzed by femtosecond time-resolved photoemission
Based on results from femtosecond time-resolved photoemission, we compare
three different methods for determination of the electron-phonon coupling
constant {\lambda} in Eu and Ba-based 122 FeAs compounds. We find good
agreement between all three methods, which reveal a small {\lambda} < 0.2. This
makes simple electron-phonon mediated superconductivity unlikely in these
compounds.Comment: 11 pages, 3 figure
Cavity QED with separate photon storage and qubit readout modes
We present the realization of a cavity quantum electrodynamics setup in which
photons of strongly different lifetimes are engineered in different harmonic
modes of the same cavity. We achieve this in a superconducting transmission
line resonator with superconducting qubits coupled to the different modes. One
cavity mode is strongly coupled to a detection line for qubit state readout,
while a second long lifetime mode is used for photon storage and coherent
quantum operations. We demonstrate sideband based measurement of photon
coherence, generation of n photon Fock states and the scaling of the sideband
Rabi frequency with the square root of n using a scheme that may be extended to
realize sideband based two-qubit logic gates.Comment: 4 pages, 5 figures, version with high resolution figures available at
http://qudev.ethz.ch/content/science/PubsPapers.htm
Student Perceptions of Teaching Assistants (TAs)
TAs perform a variety of teaching tasks in basic communication courses, but little empirical data exists to document the effectiveness of TA teaching ability or provide insight into how basic course directors and others involved in TA training might enhance their ability. The two studies presented herein provide descriptions of undergraduate students\u27 perceptions of TAs as instructors. Results suggest that professionalism and communication skills are perceptions. Suggestions are provided for how to focus TA training on those critical variables
Photon State Tomography for Two-Mode Correlated Itinerant Microwave Fields
Continuous variable entanglement between two modes of a radiation field is
usually studied at optical frequencies. As an important step towards the
observation of entanglement between propagating microwave photons we
demonstrate the experimental state reconstruction of two field modes in the
microwave domain. In particular, we generate two-mode correlated states with a
Josephson parametric amplifier and detect all four quadrature components
simultaneously in a two-channel heterodyne setup using amplitude detectors.
Analyzing two-dimensional phase space histograms for all possible pairs of
quadratures allows us to determine the full covariance matrix and reconstruct
the four-dimensional Wigner function. We demonstrate strong correlations
between the quadrature amplitude noise in the two modes. Under ideal conditions
two-mode squeezing below the standard quantum limit should be observable in
future experiments.Comment: 4 pages, 4 figure
Geometric Phase and Non-Adiabatic Effects in an Electronic Harmonic Oscillator
Steering a quantum harmonic oscillator state along cyclic trajectories leads
to a path-dependent geometric phase. Here we describe an experiment observing
this geometric phase in an electronic harmonic oscillator. We use a
superconducting qubit as a non-linear probe of the phase, otherwise
unobservable due to the linearity of the oscillator. Our results demonstrate
that the geometric phase is, for a variety of cyclic trajectories, proportional
to the area enclosed in the quadrature plane. At the transition to the
non-adiabatic regime, we study corrections to the phase and dephasing of the
qubit caused by qubit-resonator entanglement. The demonstrated controllability
makes our system a versatile tool to study adiabatic and non-adiabatic
geometric phases in open quantum systems and to investigate the potential of
geometric gates for quantum information processing
Time reversal in thermoacoustic tomography - an error estimate
The time reversal method in thermoacoustic tomography is used for
approximating the initial pressure inside a biological object using
measurements of the pressure wave made on a surface surrounding the object.
This article presents error estimates for the time reversal method in the cases
of variable, non-trapping sound speeds.Comment: 16 pages, 6 figures, expanded "Remarks and Conclusions" section,
added one figure, added reference
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