2,007 research outputs found
Non-Markovian Quantum Trajectories of Many-Body Quantum Open Systems
A long-standing open problem in non-Markovian quantum state diffusion (QSD)
approach to open quantum systems is to establish the non-Markovian QSD
equations for multiple qubit systems. In this paper, we settle this important
question by explicitly constructing a set of exact time-local QSD equations for
-qubit systems. Our exact time-local (convolutionless) QSD equations have
paved the way towards simulating quantum dynamics of many-body open systems
interacting with a common bosonic environment. The applicability of this
multiple-qubit stochastic equation is exemplified by numerically solving
several quantum open many-body systems concerning quantum coherence dynamics
and dynamical control.Comment: 8 pages, 2 figures. manuscript revised and reference update
Demonstration of Maxwell Demon-assistant Einstein-Podolsky-Rosen Steering via Superconducting Quantum Processor
The concept of Maxwell demon plays an essential role in connecting
thermodynamics and information theory, while entanglement and non-locality are
fundamental features of quantum theory. Given the rapid advancements in the
field of quantum information science, there is a growing interest and
significance in investigating the connection between Maxwell demon and quantum
correlation. The majority of research endeavors thus far have been directed
towards the extraction of work from quantum correlation through the utilization
of Maxwell demon. Recently, a novel concept called Maxwell demon-assistant
Einstein-Podolsky-Rosen (EPR) steering has been proposed, which suggests that
it is possible to simulate quantum correlation by doing work. This seemingly
counterintuitive conclusion is attributed to the fact that Alice and Bob need
classical communication during EPR steering task, a requirement that does not
apply in the Bell test. In this study, we demonstrate Maxwell demon-assistant
EPR steering with superconducting quantum circuits. By compiling and optimizing
a quantum circuit to be implemented on a 2D superconducting chip, we were able
to achieve a steering parameter of in the case of two
measurement settings, which surpasses the classical bound of by
12.6 standard deviations. In addition, experimental observations have revealed
a linear correlation between the non-locality demonstrated in EPR steering and
the work done by the demon. Considering the errors in practical operation, the
experimental results are highly consistent with theoretical predictions. Our
findings not only suggest the presence of a Maxwell demon loophole in the EPR
steering, but also contribute to a deeper comprehension of the interplay
between quantum correlation, information theory, and thermodynamics.Comment: Comments are welcome
Annealing-Dependent Magnetic Depth Profile in Ga[1-x]Mn[x]As
We have studied the depth-dependent magnetic and structural properties of
as-grown and optimally annealed Ga[1-x]Mn[x]As films using polarized neutron
reflectometry. In addition to increasing total magnetization, the annealing
process was observed to produce a significantly more homogeneous distribution
of the magnetization. This difference in the films is attributed to the
redistribution of Mn at interstitial sites during the annealing process. Also,
we have seen evidence of significant magnetization depletion at the surface of
both as-grown and annealed films.Comment: 5 pages, 3 figure
Transition from sign-reversed to sign-preserved Cooper-pairing symmetry in sulfur-doped iron selenide superconductors
An essential step toward elucidating the mechanism of superconductivity is to
determine the sign/phase of superconducting order parameter, as it is closely
related to the pairing interaction. In conventional superconductors, the
electron-phonon interaction induces attraction between electrons near the Fermi
energy and results in a sign-preserved s-wave pairing. For high-temperature
superconductors, including cuprates and iron-based superconductors, prevalent
weak coupling theories suggest that the electron pairing is mediated by spin
fluctuations which lead to repulsive interactions, and therefore that a
sign-reversed pairing with an s+-or d-wave symmetry is favored. Here, by using
magnetic neutron scattering, a phase sensitive probe of superconducting gap, we
report the observation of a transition from the sign-reversed to sign-preserved
Cooper-pairing symmetry with insignificant changes in Tc in the S-doped iron
selenide superconductors KxFe2-y(Se1-zSz)2. We show that a rather sharp
magnetic resonant mode well below the superconducting gap (2delta) in the
undoped sample (z = 0) is replaced by a broad hump structure above 2delta under
50% S doping. These results cannot be readily explained by simple spin
fluctuation-exchange pairing theories and, therefore, multiple pairing channels
are required to describe superconductivity in this system. Our findings may
also yield a simple explanation for the sometimes contradictory data on the
sign of the superconducting order parameter in iron-based materials.Comment: 11 pages, 4 figures, Supplemental Materials available upon reques
Magnetic spin excitations in Mn doped GaAs : A model study
We provide a quantitative theoretical model study of the dynamical magnetic
properties of optimally annealed GaMnAs. This model has already
been shown to reproduce accurately the Curie temperatures for
GaMnAs. Here we show that the calculated spin stiffness are in
excellent agreement with those which were obtained from ab-initio based
studies. In addition, an overall good agreement is also found with available
experimental data. We have also evaluated the magnon density of states and the
typical density of states from which the "mobility edge", separating the
extended from localized magnon states, was determined. The power of the model
lies in its ability to be generalized for a broad class of diluted magnetic
semiconductor materials, thus it bridges the gap between first principle
calculations and model based studies.Comment: 5 pages, 5 figures, Text and some figures revised to match the
accepted versio
Structural and magnetic phase diagram of CeFeAsO1-xFx and its relationship to high-temperature superconductivity
We use neutron scattering to study the structural and magnetic phase
transitions in the iron pnictides CeFeAsO1-xFx as the system is tuned from a
semimetal to a high-transition-temperature (high-Tc) superconductor through
Fluorine (F) doping x. In the undoped state, CeFeAsO develops a structural
lattice distortion followed by a stripe like commensurate antiferromagnetic
order with decreasing temperature. With increasing Fluorine doping, the
structural phase transition decreases gradually while the antiferromagnetic
order is suppressed before the appearance of superconductivity, resulting an
electronic phase diagram remarkably similar to that of the high-Tc copper
oxides. Comparison of the structural evolution of CeFeAsO1-xFx with other
Fe-based superconductors reveals that the effective electronic band width
decreases systematically for materials with higher Tc. The results suggest that
electron correlation effects are important for the mechanism of high-Tc
superconductivity in these Fe pnictides.Comment: 19 pages, 5 figure
Fluorescence Quenching of Alpha-Fetoprotein by Gold Nanoparticles: Effect of Dielectric Shell on Non-Radiative Decay
Fluorescence quenching spectrometry was applied to study the interactions between gold colloidal nanoparticles and alpha-fetoprotein (AFP). Experimental results show that the gold nanoparticles can quench the fluorescence emission of adsorbed AFP effectively. Furthermore, the intensity of fluorescence emission peak decreases monotonously with the increasing gold nanoparticles content. A mechanism based on surface plasmon resonance–induced non-radiative decay was investigated to illuminate the effect of a dielectric shell on the fluorescence quenching ability of gold nanoparticles. The calculation results show that the increasing dielectric shell thickness may improve the monochromaticity of fluorescence quenching. However, high energy transfer efficiency can be obtained within a wide wavelength band by coating a thinner dielectric shell
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