1,759 research outputs found
Perspectives for analyzing non-linear photo-ionization spectra with deep neural networks trained with synthetic Hamilton matrices
We have constructed deep neural networks, which can map fluctuating photo-electron spectra obtained from noisy pulses to spectra from noise-free pulses. The network is trained on spectra from noisy pulses in combination with random Hamilton matrices, representing systems which could exist but do not necessarily exist. In [Giri et al., Phys. Rev. Lett., 2020, 124, 113201] we performed a purification of fluctuating spectra, that is, mapping them to those from Fourier-limited Gaussian pulses. Here, we investigate the performance of such neural-network-based maps for predicting spectra of double pulses, pulses with a chirp and even partially-coherent pulses from fluctuating spectra generated by noisy pulses. Secondly, we demonstrate that along with purification of a fluctuating double-pulse spectrum, one can estimate the time-delay of the underlying double pulse, an attractive feature for single-shot spectra from SASE FELs. We demonstrate our approach with resonant two-photon ionization, a non-linear process, sensitive to details of the laser pulse
The brachistochrone problem in open quantum systems
Recently, the quantum brachistochrone problem is discussed in the literature
by using non-Hermitian Hamilton operators of different type. Here, it is
demonstrated that the passage time is tunable in realistic open quantum systems
due to the biorthogonality of the eigenfunctions of the non-Hermitian Hamilton
operator. As an example, the numerical results obtained by Bulgakov et al. for
the transmission through microwave cavities of different shape are analyzed
from the point of view of the brachistochrone problem. The passage time is
shortened in the crossover from the weak-coupling to the strong-coupling regime
where the resonance states overlap and many branch points (exceptional points)
in the complex plane exist. The effect can {\it not} be described in the
framework of standard quantum mechanics with Hermitian Hamilton operator and
consideration of matrix poles.Comment: 18 page
Isotope Shifts of the 6d\,^2D - 7p\,^2P Transition in Trapped Short-Lived Ra
Laser spectroscopy of short-lived radium isotopes in a linear Paul trap has
been performed. The isotope shifts of the 6d\,^2D -
7p\,^2P transition in Ra were measured, which are
sensitive to the short range part of the atomic wavefunctions. The results are
essential experimental input for improving the precision of atomic structure
calculation. This is indispensable for parity violation in Ra aiming at the
determination of the weak mixing angle.Comment: Accepted for publication in Physical Review A as a Rapid
Communicatio
Search for B+ →μ+νμ and B+ →μ+N with inclusive tagging
We report the result for a search for the leptonic decay of B+→μ+νμ using the full Belle dataset of 711 fb-1 of integrated luminosity at the (4S) resonance. In the Standard Model leptonic B-meson decays are helicity and Cabibbo-Kobayashi-Maskawa suppressed. To maximize sensitivity an inclusive tagging approach is used to reconstruct the second B meson produced in the collision. The directional information from this second B meson is used to boost the observed μ into the signal B-meson rest frame, in which the μ has a monochromatic momentum spectrum. Though its momentum is smeared by the experimental resolution, this technique improves the analysis sensitivity considerably. Analyzing the μ momentum spectrum in this frame we find B(B+→μ+νμ)=(5.3±2.0±0.9)×10-7 with a one-sided significance of 2.8 standard deviations over the background-only hypothesis. This translates to a frequentist upper limit of B(B+→μ+νμ)<8.6×10-7 at 90% confidence level. The experimental spectrum is then used to search for a massive sterile neutrino, B+→μ+N, but no evidence is observed for a sterile neutrino with a mass in a range of 0-1.5 GeV. The determined B+→μ+νμ branching fraction limit is further used to constrain the mass and coupling space of the type II and type III two-Higgs-doublet models. © 2020 authors. Published by the American Physical Society
Spectroscopic investigation of quantum confinement effects in ion implanted silicon-on-sapphire films
Crystalline Silicon-on-Sapphire (SOS) films were implanted with boron (B)
and phosphorous (P) ions. Different samples, prepared by varying the ion
dose in the range to 5 x and ion energy in the range
150-350 keV, were investigated by the Raman spectroscopy, photoluminescence
(PL) spectroscopy and glancing angle x-ray diffraction (GAXRD). The Raman
results from dose dependent B implanted samples show red-shifted and
asymmetrically broadened Raman line-shape for B dose greater than
ions cm. The asymmetry and red shift in the Raman line-shape is
explained in terms of quantum confinement of phonons in silicon nanostructures
formed as a result of ion implantation. PL spectra shows size dependent visible
luminescence at 1.9 eV at room temperature, which confirms the presence
of silicon nanostructures. Raman studies on P implanted samples were also
done as a function of ion energy. The Raman results show an amorphous top SOS
surface for sample implanted with 150 keV P ions of dose 5 x ions
cm. The nanostructures are formed when the P energy is increased to
350 keV by keeping the ion dose fixed. The GAXRD results show consistency with
the Raman results.Comment: 9 Pages, 6 Figures and 1 Table, \LaTex format To appear in
SILICON(SPRINGER
Computed Rotational Collision Rate Coefficients for Recently Detected Anionic Cyanopolyynes
We report new results from quantum calculations of energy-transfer processes
taking place in interstellar environments and involving two newly observed
molecular species: CN and CN in collision with He atoms and the
p-H molecules. These species are part of the anionic molecular chains
labeled as cyanopolyynes which have been observed over the years in
molecule-rich Circumstellar Envelopes and in molecular clouds. In the present
work, we first carry out new calculations for the CN
interaction potential with He atom and then obtain state-to-state rotationally
inelastic cross sections and rate coefficients involving the same transitions
which have been observed experimentally by emission in the interstellar medium
(ISM) from both of these linear species. For the CN/He system we extend
the calculations already published in our earlier work (see reference below) to
compare more directly the two molecular anions. We extend further the quantum
calculations by also computing in this work collision rate coefficients for the
hydrogen molecule interacting with C5N, using our previously computed
interaction potential. Additionally, we obtain the same rate coefficients for
the CN/H system by using a scaling procedure that makes use of the
new CN/He rate coefficients, as discussed in detail in the present
paper. Their significance in affecting internal state populations in ISM
environments where the title anions have been found is analyzed by using the
concept of critical density indicators. Finally, similarities and differences
between such species and the comparative efficiency of their collision rate
coefficients are discussed. These new calculations suggest that, at least for
the case of these longer chains, the rotational populations could reach local
thermal equilibrium conditions within their observational environments
Heavy Fermion Behavior, Crystalline Electric Field Effects, and Weak Ferromagnetism in SmOs_{4}Sb_{12}
The filled skutterudite compound SmOs_{4}Sb_{12} was prepared in single
crystal form and characterized. The SmOs_{4}Sb_{12} crystals have the
LaFe_{4}P_{12}-type structure with lattice parameter a = 9.3085 Angstroms.
Specific heat measurements indicate a large electronic specific heat
coefficient of ~880 mJ/mol K^{2}, from which an enhanced effective mass m^{*} ~
170 m_{e} is estimated. The specific heat data also suggest crystalline
electric field (CEF) splitting of the Sm^{3+} J = 5/2 multiplet into a
Gamma_{7} doublet ground state and a Gamma_{8} quartet excited state separated
by 37 K. Electrical resistivity rho(T) measurements reveal a decrease in rho(T)
below ~50 K that is consistent with CEF splitting of ~33 K between a Gamma_(7)
doublet ground state and Gamma_{8} quartet excited state. Specific heat and
magnetic susceptibility measurements display a possible weak ferromagnetic
transition at ~2.6 K, which could be an intrinsic property of SmOs_4Sb_{12} or
possibly due to an unknown impurity phase.Comment: 24 pages, 11 Postscript figures, to be published in Physical Review
Lower bound of minimal time evolution in quantum mechanics
We show that the total time of evolution from the initial quantum state to
final quantum state and then back to the initial state, i.e., making a round
trip along the great circle over S^2, must have a lower bound in quantum
mechanics, if the difference between two eigenstates of the 2\times 2
Hamiltonian is kept fixed. Even the non-hermitian quantum mechanics can not
reduce it to arbitrarily small value. In fact, we show that whether one uses a
hermitian Hamiltonian or a non-hermitian, the required minimal total time of
evolution is same. It is argued that in hermitian quantum mechanics the
condition for minimal time evolution can be understood as a constraint coming
from the orthogonality of the polarization vector \bf P of the evolving quantum
state \rho={1/2}(\bf 1+ \bf{P}\cdot\boldsymbol{\sigma}) with the vector
\boldsymbol{\mathcal O}(\Theta) of the 2\times 2 hermitian Hamiltonians H
={1/2}({\mathcal O}_0\boldsymbol{1}+ \boldsymbol{\mathcal
O}(\Theta)\cdot\boldsymbol{\sigma}) and it is shown that the Hamiltonian H can
be parameterized by two independent parameters {\mathcal O}_0 and \Theta.Comment: 4 pages, no figure, revtex
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