124 research outputs found
Nonclassical Moments and their Measurement
Practically applicable criteria for the nonclassicality of quantum states are
formulated in terms of different types of moments. For this purpose the moments
of the creation and annihilation operators, of two quadratures, and of a
quadrature and the photon number operator turn out to be useful. It is shown
that all the required moments can be determined by homodyne correlation
measurements. An example of a nonclassical effect that is easily characterized
by our methods is amplitude-squared squeezing.Comment: 12 pages, 6 figure
First-Order Type Effects in YBaCuO at the Onset of Superconductivity
We present results of Raman scattering experiments on tetragonal for doping levels between 0 and
0.07 holes/CuO. Below the onset of superconductivity at , we find evidence of a diagonal superstructure. At ,
lattice and electron dynamics change discontinuously with the charge and spin
properties being renormalized at all energy scales. The results indicate that
charge ordering is intimately related to the transition at and
that the maximal transition temperature to superconductivity at optimal doping
depends on the type of ordering at .Comment: 4 pages, 4 figure
Band and momentum dependent electron dynamics in superconducting as seen via electronic Raman scattering
We present details of carrier properties in high quality single crystals obtained from electronic Raman
scattering. The experiments indicate a strong band and momentum anisotropy of
the electron dynamics above and below the superconducting transition
highlighting the importance of complex band-dependent interactions. The
presence of low energy spectral weight deep in the superconducting state
suggests a gap with accidental nodes which may be lifted by doping and/or
impurity scattering. When combined with other measurements, our observation of
band and momentum dependent carrier dynamics indicate that the iron arsenides
may have several competing superconducting ground states.Comment: 5 pages, 4 figure
Electron-boson glue function derived from electronic Raman scattering
Raman scattering cross sections depend on photon polarization. In the
cuprates nodal and antinodal directions are weighted more strongly in
and symmetry, respectively. On the other hand in angle-resolved
photoemission spectroscopy (ARPES), electronic properties are measured along
well-defined directions in momentum space rather than their weighted averages.
In contrast, the optical conductivity involves a momentum average over the
entire Brillouin zone. Newly measured Raman response data on high-quality
BiSrCaCuO single crystals up to high energies have
been inverted using a modified maximum entropy inversion technique to extract
from and Raman data corresponding electron-boson spectral
densities (glue) are compared to the results obtained with known ARPES and
optical inversions. We find that the spectrum agrees qualitatively
with nodal direction ARPES while the looks more like the optical
spectrum. A large peak around meV in , much less prominent
in , is taken as support for the importance of scattering
at this frequency.Comment: 7 pages, 3 figure
Electron interactions and charge ordering in LaSrCuO
We present results of inelastic light scattering experiments on
single-crystalline LaSrCuO in the doping range and TlBaCuO at and . The main
emphasis is placed on the response of electronic excitations in the
antiferromagnetic phase, in the pseudogap range, in the superconducting state,
and in the essentially normal metallic state at , where no
superconductivity could be observed. In most of the cases we compare B
and B spectra which project out electronic properties close to
and , respectively. In the channel of electron-hole excitations
we find universal behavior in B symmetry as long as the material
exhibits superconductivity at low temperature. In contrast, there is a strong
doping dependence in B symmetry: (i) In the doping range we observe rapid changes of shape and temperature dependence of the
spectra. (ii) In LaSrCuO new structures appear for
which are superposed on the electron-hole continuum. The temperature dependence
as well as model calculations support an interpretation in terms of
charge-ordering fluctuations. For the response from fluctuations
disappears at B and appears at B symmetry in full agreement with
the orientation change of stripes found by neutron scattering. While, with a
grain of salt, the particle-hole continuum is universal for all cuprates the
response from fluctuating charge order in the range is so
far found only in LaSrCuO. We conclude that
LaSrCuO is close to static charge order and, for this reason,
may have a suppressed .Comment: 17 pages, 15 figure
Quantum utility -- definition and assessment of a practical quantum advantage
Several benchmarks have been proposed to holistically measure quantum
computing performance. While some have focused on the end user's perspective
(e.g., in application-oriented benchmarks), the real industrial value taking
into account the physical footprint of the quantum processor are not discussed.
Different use-cases come with different requirements for size, weight, power
consumption, or data privacy while demanding to surpass certain thresholds of
fidelity, speed, problem size, or precision. This paper aims to incorporate
these characteristics into a concept coined quantum utility, which demonstrates
the effectiveness and practicality of quantum computers for various
applications where quantum advantage -- defined as either being faster, more
accurate, or demanding less energy -- is achieved over a classical machine of
similar size, weight, and cost. To successively pursue quantum utility, a
level-based classification scheme -- constituted as application readiness
levels (ARLs) -- as well as extended classification labels are introduced.
These are demonstratively applied to different quantum applications from the
fields of quantum chemistry, quantum simulation, quantum machine learning, and
data analysis followed by a brief discussion
An Investigation of Particle-Hole Asymmetry in the Cuprates via Electronic Raman Scattering
In this paper we examine the effects of electron-hole asymmetry as a
consequence of strong correlations on the electronic Raman scattering in the
normal state of copper oxide high temperature superconductors. Using
determinant quantum Monte Carlo simulations of the single-band Hubbard model,
we construct the electronic Raman response from single particle Green's
functions and explore the differences in the spectra for electron and hole
doping away from half filling. The theoretical results are compared to new and
existing Raman scattering experiments on hole-doped LaSrCuO
and electron-doped NdCeCuO. These findings suggest that the
Hubbard model with fixed interaction strength qualitatively captures the doping
and temperature dependence of the Raman spectra for both electron and hole
doped systems, indicating that the Hubbard parameter U does not need to be
doping dependent to capture the essence of this asymmetry.Comment: 13 pages, 10 figure
Uncertainty Relations in Deformation Quantization
Robertson and Hadamard-Robertson theorems on non-negative definite hermitian
forms are generalized to an arbitrary ordered field. These results are then
applied to the case of formal power series fields, and the
Heisenberg-Robertson, Robertson-Schr\"odinger and trace uncertainty relations
in deformation quantization are found. Some conditions under which the
uncertainty relations are minimized are also given.Comment: 28+1 pages, harvmac file, no figures, typos correcte
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