213 research outputs found
Continuous matrix product state tomography of quantum transport experiments
In recent years, a close connection between the description of open quantum
systems, the input-output formalism of quantum optics, and continuous matrix
product states in quantum field theory has been established. So far, however,
this connection has not been extended to the condensed-matter context. In this
work, we substantially develop further and apply a machinery of continuous
matrix product states (cMPS) to perform tomography of transport experiments. We
first present an extension of the tomographic possibilities of cMPS by showing
that reconstruction schemes do not need to be based on low-order correlation
functions only, but also on low-order counting probabilities. We show that
fermionic quantum transport settings can be formulated within the cMPS
framework. This allows us to present a reconstruction scheme based on the
measurement of low-order correlation functions that provides access to
quantities that are not directly measurable with present technology. Emblematic
examples are high-order correlations functions and waiting times distributions
(WTD). The latter are of particular interest since they offer insights into
short-time scale physics. We demonstrate the functioning of the method with
actual data, opening up the way to accessing WTD within the quantum regime.Comment: 11 pages, 4 figure
Dielectric screening in extended systems using the self-consistent Sternheimer equation and localized basis sets
We develop a first-principles computational method for investigating the
dielectric screening in extended systems using the self-consistent Sternheimer
equation and localized non-orthogonal basis sets. Our approach does not require
the explicit calculation of unoccupied electronic states, only uses two-center
integrals, and has a theoretical scaling of order O(N^3). We demonstrate this
method by comparing our calculations for silicon, germanium, diamond, and LiCl
with reference planewaves calculations. We show that accuracy comparable to
planewaves calculations can be achieved via a systematic optimization of the
basis set.Comment: 6 pages, 3 figure
Microscopic theory for the light-induced anomalous Hall effect in graphene
We employ a quantum Liouville equation with relaxation to model the recently
observed anomalous Hall effect in graphene irradiated by an ultrafast pulse of
circularly polarized light. In the weak-field regime, we demonstrate that the
Hall effect originates from an asymmetric population of photocarriers in the
Dirac bands. By contrast, in the strong-field regime, the system is driven into
a non-equilibrium steady state that is well-described by topologically
non-trivial Floquet-Bloch bands. Here, the anomalous Hall current originates
from the combination of a population imbalance in these dressed bands together
with a smaller anomalous velocity contribution arising from their Berry
curvature. This robust and general finding enables the simulation of electrical
transport from light-induced Floquet-Bloch bands in an experimentally relevant
parameter regime and creates a pathway to designing ultrafast quantum devices
with Floquet-engineered transport properties
Common microscopic origin of the phase transitions in Ta<sub>2</sub>NiS<sub>5</sub> and the excitonic insulator candidate Ta<sub>2</sub>NiSe<sub>5</sub>
The structural phase transition in Ta2NiSe5 has been envisioned as driven by the formation of an excitonic insulating phase. However, the role of structural and electronic instabilities on crystal symmetry breaking has yet to be disentangled. Meanwhile, the phase transition in its complementary material Ta2NiS5 does not show any experimental hints of an excitonic insulating phase. We present a microscopic investigation of the electronic and phononic effects involved in the structural phase transition in Ta2NiSe5 and Ta2NiS5 using extensive first-principles calculations. In both materials the crystal symmetries are broken by phonon instabilities, which in turn lead to changes in the electronic bandstructure also observed in the experiment. A total energy landscape analysis shows no tendency towards a purely electronic instability and we find that a sizeable lattice distortion is needed to open a bandgap. We conclude that an excitonic instability is not needed to explain the phase transition in both Ta2NiSe5 and Ta2NiS5
Local renormalization method for random systems
In this paper, we introduce a real-space renormalization transformation for
random spin systems on 2D lattices. The general method is formulated for random
systems and results from merging two well known real space renormalization
techniques, namely the strong disorder renormalization technique (SDRT) and the
contractor renormalization (CORE). We analyze the performance of the method on
the 2D random transverse field Ising model (RTFIM).Comment: 12 pages, 13 figures. Submitted to the Special Issue on "Quantum
Information and Many-Body Theory", New Journal of Physics. Editors: M.B.
Plenio, J. Eiser
ANNINE-6plus, a voltage-sensitive dye with good solubility, strong membrane binding and high sensitivity
We present a novel voltage-sensitive hemicyanine dye ANNINE-6plus and describe its synthesis, its properties and its voltage-sensitivity in neurons. The dye ANNINE-6plus is a salt with a double positively charged chromophore and two bromide counterions. It is derived from the zwitterionic dye ANNINE-6. While ANNINE-6 is insoluble in water, ANNINE-6plus exhibits a high solubility of around 1 mM. Nonetheless, it displays a strong binding to lipid membranes. In contrast to ANNINE-6, the novel dye can be used to stain cells from aqueous solution without surfactants or organic solvents. In neuronal membranes, ANNINE-6plus exhibits the same molecular Stark effect as ANNINE-6. As a consequence, a high voltage-sensitivity is achieved with illumination and detection in the red end of the excitation and emission spectra, respectively. ANNINE-6plus will be particularly useful for sensitive optical recording of neuronal excitation when organic solvents and surfactants must be avoided as with intracellular or extracellular staining of brain tissue
Entanglement entropy of two disjoint intervals in c=1 theories
We study the scaling of the Renyi entanglement entropy of two disjoint blocks
of critical lattice models described by conformal field theories with central
charge c=1. We provide the analytic conformal field theory result for the
second order Renyi entropy for a free boson compactified on an orbifold
describing the scaling limit of the Ashkin-Teller (AT) model on the self-dual
line. We have checked this prediction in cluster Monte Carlo simulations of the
classical two dimensional AT model. We have also performed extensive numerical
simulations of the anisotropic Heisenberg quantum spin-chain with tree-tensor
network techniques that allowed to obtain the reduced density matrices of
disjoint blocks of the spin-chain and to check the correctness of the
predictions for Renyi and entanglement entropies from conformal field theory.
In order to match these predictions, we have extrapolated the numerical results
by properly taking into account the corrections induced by the finite length of
the blocks to the leading scaling behavior.Comment: 37 pages, 23 figure
Chronic y-secretase inhibition reduces amyloid plaque-associated instability of pre- and postsynaptic structures
The loss of synapses is a strong histological correlate of the cognitive decline in Alzheimer’s disease (AD). Amyloid bpeptide (Ab), a cleavage product of the amyloid precursor protein (APP), exerts detrimental effects on synapses, a process thought to be causally related to the cognitive deficits in AD. Here, we used in vivo two-photon microscopy to characterize the dynamics of axonal boutons and dendritic spines in APP/Presenilin 1 (APPswe/PS1L166P)–green fluorescent protein (GFP) transgenic mice. Time-lapse imaging over 4 weeks revealed a pronounced, concerted instability of pre- and postsynaptic structures within the vicinity of amyloid plaques. Treatment with a novel sulfonamide-type g-secretase inhibitor (GSI) attenuated the formation and growth of new plaques and, most importantly, led to a normalization of the enhanced dynamics of synaptic structures close to plaques. GSI treatment did neither affect spines and boutons distant from plaques in amyloid precursor protein/presenilin 1-GFP (APPPS1-GFP) nor those in GFP-control mice, suggesting no obvious neuropathological side effects of the drug
- …