1,740 research outputs found
FQHE interferometers in strong tunneling regime. The role of compactness of edge fields
We consider multiple-point tunneling in the interferometers formed between
edges of electron liquids with in general different filling factors in the
regime of the Fractional Quantum Hall effect (FQHE). We derive an effective
matrix Caldeira-Leggett models for the multiple tunneling contacts connected by
the chiral single-mode FQHE edges. It is shown that the compactness of the Wen-
Fr\"ohlich chiral boson fields describing the FQHE edge modes plays a crucial
role in eliminating the spurious non-locality of the electron transport
properties of the FQHE interferometers arising in the regime of strong
tunneling.Comment: 5 page
Double Well Potential: Perturbation Theory, Tunneling, WKB (beyond instantons)
A simple approximate solution for the quantum-mechanical quartic oscillator
in the double-well regime at arbitrary is
presented. It is based on a combining of perturbation theory near true minima
of the potential, semi-classical approximation at large distances and a
description of tunneling under the barrier. It provides 9-10 significant digits
in energies and gives for wavefunctions the relative deviation in real
-space less than .Comment: 13 pages, invited talk at "Crossing the boundaries: Gauge dynamics at
strong coupling (Shifmania)", Minneapolis, May 14-17, 200
Generalized quantum measurements with matrix product states: Entanglement phase transition and clusterization
We propose a method, based on matrix product states, for studying the time
evolution of many-body quantum lattice systems under continuous and
site-resolved measurement. Both the frequency and the strength of generalized
measurements can be varied within our scheme, thus allowing us to explore the
corresponding two-dimensional phase diagram. The method is applied to
one-dimensional chains of nearest-neighbor interacting hard-core bosons. A
transition from an entangling to a disentangling (area-law) phase is found.
However, by resolving time-dependent density correlations in the monitored
system, we find important differences between different regions at the phase
boundary. In particular, we observe a peculiar phenomenon of
measurement-induced particle clusterization that takes place only for frequent
moderately strong measurements, but not for strong infrequent measurements.Comment: 13 pages, 11 figures, plus an appendix (13 pp., 1 figure). Comments
welcom
Evolution of many-body systems under ancilla quantum measurements
Measurement-induced phase transitions are the subject of intense current
research, both from an experimental and a theoretical perspective. We explore
the concept of implementing quantum measurements by coupling a many-body
lattice system to an ancillary degree of freedom (implemented using two
additional sites), on which projective measurements are performed. We analyze
the effect of repeated (``stroboscopic'') measurements on the dynamical
correlations of interacting hard-core bosons in a one-dimensional chain. An
important distinctive ingredient of the protocol is the fact that the detector
ancillas are not re-initialized after each measurement step. The detector thus
maintains memory of the accumulated influence by the measured correlated
system. Initially, we consider a model in which the ancilla is coupled to a
single lattice site. This setup allows obtaining information about the system
through Rabi oscillations in the ancillary degrees of freedom, modulated by the
ancilla-system interaction. The statistics of quantum trajectories exhibits a
``quantum-Zeno-valve effect'' that occurs when the measurement becomes strong,
with sharp branching between low and high entanglement. We proceed by extending
numerical simulations to the case of two ancillas and, then, to measurements on
all sites. With this realistic measurement apparatus, we find evidence of a
disentangling-entangling measurement-induced transition as was previously
observed in more abstract models. The dynamics features a broad distribution of
the entanglement entropy.Comment: 23 pages, 17 figure
Case study of ozone anomalies over northern Russia in the 2015/2016 winter: measurements and numerical modelling
Episodes of extremely low ozone columns were observed over the territory of
Russia in the Arctic winter of 2015/2016 and the beginning of spring 2016. We
compare total ozone columns (TOCs) from different remote sensing techniques
(satellite and ground-based observations) with results of numerical modelling
over the territory of the Urals and Siberia for this period. We demonstrate
that the provided monitoring systems (including the new Russian Infrared
Fourier Spectrometer IKFS-2) and modern three-dimensional atmospheric models
can capture the observed TOC anomalies. However, the results of observations
and modelling show differences of up to 20 %–30 % in TOC
measurements. Analysis of the role of chemical and dynamical processes
demonstrates that the observed short-term TOC variability is not a result of
local photochemical loss initiated by heterogeneous halogen activation on
particles of polar stratospheric clouds that formed under low temperatures in
the mid-winter.</p
Eco-friendly iron-humic nanofertilizers synthesis for the prevention of iron chlorosis in soybean (Glycine max) grown in calcareous soil
Iron deficiency is a frequent problem for many crops, particularly in calcareous soils and iron humates are commonly applied in the Mediterranean basin in spite of their lesser efficiency than iron synthetic chelates. Development and application of new fertilizers using nanotechnology are one of the potentially effective options of enhancing the iron humates, according to the sustainable agriculture. Particle size, pH, and kinetics constrain the iron humate efficiency. Thus, it is relevant to understand the iron humate mechanism in the plant–soil system linking their particle size, characterization and iron distribution in plant and soil using 57Fe as a tracer tool. Three hybrid nanomaterials (F, S, and M) were synthesized as iron-humic nanofertilizers (57Fe-NFs) from leonardite potassium humate and 57Fe used in the form of 57Fe(NO3)3 or 57Fe2(SO4)3. They were characterized using Mössbauer spectroscopy, X-ray diffraction (XRD), extended X-ray absorption fine structure spectroscopy (EXAFS), transmission electron microscopy (TEM) and tested for iron availability in a calcareous soil pot experiment carried out under growth chamber conditions. Three doses (35, 75, and 150 mmol pot-1) of each iron-humic material were applied to soybean iron deficient plants and their iron nutrition contributions were compared to 57FeEDDHA and leonardite potassium humate as control treatments. Ferrihydrite was detected as the main structure of all three 57Fe- NFs and the plants tested with iron-humic compounds exhibited continuous long-term statistically reproducible iron uptake and showed high shoot fresh weight. Moreover, the 57Fe from the humic nanofertilizers remained available in soil and was detected in soybean pods. The Fe-NFs offers a natural, low cost and environmental option to the traditional iron fertilization in calcareous soilsThe Russian Science Foundation (16-14-00167), the Russian Foundation for Basic Research (18-29-25065), and the Spanish Ministry of Science and Innovation (AGL2013-44474-R) have financially supported this research
Many-body localization and delocalization in large quantum chains
We theoretically study the quench dynamics for an isolated Heisenberg spin
chain with a random on-site magnetic field, which is one of the paradigmatic
models of a many-body localization transition. We use the time-dependent
variational principle as applied to matrix product states, which allows us to
controllably study chains of a length up to spins, i.e., much larger
than that can be treated via exact diagonalization. For the
analysis of the data, three complementary approaches are used: (i)
determination of the exponent which characterizes the power-law decay
of the antiferromagnetic imbalance with time; (ii) similar determination of the
exponent which characterizes the decay of a Schmidt gap in the
entanglement spectrum, (iii) machine learning with the use, as an input, of the
time dependence of the spin densities in the whole chain. We find that the
consideration of the larger system sizes substantially increases the estimate
for the critical disorder that separates the ergodic and many-body
localized regimes, compared to the values of in the literature. On the
ergodic side of the transition, there is a broad interval of the strength of
disorder with slow subdiffusive transport. In this regime, the exponents
and increase, with increasing , for relatively small
but saturate for , indicating that these slow power laws
survive in the thermodynamic limit. From a technical perspective, we develop an
adaptation of the "learning by confusion" machine learning approach that can
determine .Comment: 14 pages, 11 figures. Title changed compared to earlier arXiv
versions. Comments welcom
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