544 research outputs found
High-Precision Observable Estimation with Single Qubit Quantum Memory
The estimation of multi-qubit observables is a key task in quantum
information science. The standard approach is to decompose a multi-qubit
observable into a weighted sum of Pauli strings. The observable can then be
estimated from projective single qubit measurements according to the Pauli
strings followed by a classical summation. As the number of Pauli strings in
the decomposition increases, shot-noise drastically builds up, and the accuracy
of such estimation can be considerably compromised. Access to a single qubit
quantum memory, where measurement data may be stored and accumulated can
circumvent the build-up of shot noise. Here, we describe a many-qubit
observable estimation approach to achieve this with a much lower number of
interactions between the multi-qubit device and the single qubit memory
compared to previous approaches. Our algorithm offers a reduction in the
required number of measurements for a given target variance that scales
with the number of Pauli strings in the observable
decomposition. The low number of interactions between the multi-qubit device
and the memory is desirable for noisy intermediate-scale quantum devices.Comment: 20 pages, 4 figures, 1 table. arXiv admin note: text overlap with
arXiv:2212.0771
Ferromagnetic Domain Structure of La0.78Ca0.22MnO3 Single Crystals
The magneto-optical technique has been employed to observe spontaneous
ferromagnetic domain structures in La0.78Ca0.22MnO3 single crystals. The
magnetic domain topology was found to be correlated with the intrinsic twin
structure of the investigated crystals. With decreasing temperature the regular
network of ferromagnetic domains undergoes significant changes resulting in
apparent rotation of the domain walls in the temperature range of 70-150 K. The
apparent rotation of the domain walls can be understood in terms of the
Jahn-Teller deformation of the orthorhombic unit cell, accompanied by
additional twinning.Comment: 7 pages, 5 figures, to be published in PR
Green's-function theory of the Heisenberg ferromagnet in a magnetic field
We present a second-order Green's-function theory of the one- and
two-dimensional S=1/2 ferromagnet in a magnetic field based on a decoupling of
three-spin operator products, where vertex parameters are introduced and
determined by exact relations. The transverse and longitudinal spin correlation
functions and thermodynamic properties (magnetization, isothermal magnetic
susceptibility, specific heat) are calculated self-consistently at arbitrary
temperatures and fields. In addition, exact diagonalizations on finite lattices
and, in the one-dimensional case, exact calculations by the Bethe-ansatz method
for the quantum transfer matrix are performed. A good agreement of the
Green's-function theory with the exact data, with recent quantum Monte Carlo
results, and with the spin polarization of a quantum Hall ferromagnet
is obtained. The field dependences of the position and height of the maximum in
the temperature dependence of the susceptibility are found to fit well to power
laws, which are critically analyzed in relation to the recently discussed
behavior in Landau's theory. As revealed by the spin correlation functions and
the specific heat at low fields, our theory provides an improved description of
magnetic short-range order as compared with the random phase approximation. In
one dimension and at very low fields, two maxima in the temperature dependence
of the specific heat are found. The Bethe-ansatz data for the field dependences
of the position and height of the low-temperature maximum are described by
power laws. At higher fields in one and two dimensions, the temperature of the
specific heat maximum linearly increases with the field.Comment: 9 pages, 9 figure
A correlated-polaron electronic propagator: open electronic dynamics beyond the Born-Oppenheimer approximation
In this work we develop a theory of correlated many-electron dynamics dressed
by the presence of a finite-temperature harmonic bath. The theory is based on
the ab-initio Hamiltonian, and thus well-defined apart from any
phenomenological choice of collective basis states or electronic coupling
model. The equation-of-motion includes some bath effects non-perturbatively,
and can be used to simulate line- shapes beyond the Markovian approximation and
open electronic dynamics which are subjects of renewed recent interest. Energy
conversion and transport depend critically on the ratio of electron-electron
coupling to bath-electron coupling, which is a fitted parameter if a
phenomenological basis of many-electron states is used to develop an electronic
equation of motion. Since the present work doesn't appeal to any such basis, it
avoids this ambiguity. The new theory produces a level of detail beyond the
adiabatic Born-Oppenheimer states, but with cost scaling like the
Born-Oppenheimer approach. While developing this model we have also applied the
time-convolutionless perturbation theory to correlated molecular excitations
for the first time. Resonant response properties are given by the formalism
without phenomenological parameters. Example propagations with a developmental
code are given demonstrating the treatment of electron-correlation in
absorption spectra, vibronic structure, and decay in an open system.Comment: 25 pages 7 figure
Phase shift rule with the optimal parameter selection
The phase shift rules enable the estimation of the derivative of a quantum
state with respect to phase parameters, providing valuable insights into the
behavior and dynamics of quantum systems. This capability is essential in
quantum simulation tasks where understanding the behavior of complex quantum
systems is of interest, such as simulating chemical reactions or condensed
matter systems. However, parameter shift rules are typically designed for
Hamiltonian systems with equidistant eigenvalues. For systems with closely
spaced eigenvalues, effective rules have not been established. We provide
insights about the optimal design of a parameter shift rule, tailored to
various sorts of spectral information that may be available. The proposed
method lets derivatives be calculated for any system, regardless of how close
the eigenvalues are to each other. It also optimizes the number of phase
shifts, which reduces the amount of gate resources needed.Comment: 24 pages, 2 figure
Metastable resistivity of La0.8Ca0.2MnO3 manganite thin films
Transport properties of La0.8Ca0.2MnO3 thin films 15 and 130 nm thick have been investigated and confronted with the properties of bulk single crystals of the same composition. It has been found that low-temperature resistivity of the films is sensitive to electric current and/or field treatment and thermal history of the sample. Thin films exhibit a variety of metastable resistive states and spontaneously evolve toward high-resistivity state in which the films exhibit highly nonlinear transport behavior at low temperatures. Nonlinear V-I characteristics are well described by indirect tunneling model. The memory of the resistivity can be, at least partly, erased by a heat treatment at temperatures above the memory erasing temperature. The memory erasing temperature for thin films, T=450 K, is significantly higher than that of single crystals. The results are interpreted in the context of strain driven phase separation. Coexistence of two ferromagnetic phases with different orbital orders and different conductivities is influenced by strains due to thermal cycling and current flow.published_or_final_versio
Magnetic irreversibility and Verwey transition in nano-crystalline bacterial magnetite
The magnetic properties of biologically-produced magnetite nanocrystals
biomineralized by four different magnetotactic bacteria were compared to those
of synthetic magnetite nanocrystals and large, high quality single crystals.
The magnetic feature at the Verwey temperature, , was clearly seen in
all nanocrystals, although its sharpness depended on the shape of individual
nanoparticles and whether or not the particles were arranged in magnetosome
chains. The transition was broader in the individual superparamagnetic
nanoparticles for which , where is the superparamagnetic
blocking temperature. For the nanocrystals organized in chains, the effective
blocking temperature and the Verwey transition is sharply
defined. No correlation between the particle size and was found.
Furthermore, measurements of suggest that magnetosome chains
behave as long magnetic dipoles where the local magnetic field is directed
along the chain and this result confirms that time-logarithmic magnetic
relaxation is due to the collective (dipolar) nature of the barrier for
magnetic moment reorientation
Transmission tree of the highly pathogenic avian influenza (H5N1) epidemic in Israel, 2015
The transmission tree of the Israeli 2015 epidemic of highly pathogenic avian influenza (H5N1) was modelled by combining the spatio-temporal distribution of the outbreaks and the genetic distance between virus isolates. The most likely successions of transmission events were determined and transmission parameters were estimated. It was found that the median infectious pressure exerted at 1 km was 1.59 times (95% CI 1.04, 6.01) and 3.54 times (95% CI 1.09, 131.75) higher than that exerted at 2 and 5 km, respectively, and that three farms were responsible for all seven transmission events. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1186/s13567-016-0393-2) contains supplementary material, which is available to authorized users
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