13,294 research outputs found
Entanglement Energetics at Zero Temperature
We show how many-body ground state entanglement information may be extracted
from sub-system energy measurements at zero temperature. Generically, the
larger the measured energy fluctuations are, the larger the entanglement is.
Examples are given with the two-state system and the harmonic oscillator.
Comparisons made with recent qubit experiments show this type of measurement
provides another method to quantify entanglement with the environment.Comment: 4 pages, 2 figure
A Temporal Logic for Hyperproperties
Hyperproperties, as introduced by Clarkson and Schneider, characterize the
correctness of a computer program as a condition on its set of computation
paths. Standard temporal logics can only refer to a single path at a time, and
therefore cannot express many hyperproperties of interest, including
noninterference and other important properties in security and coding theory.
In this paper, we investigate an extension of temporal logic with explicit path
variables. We show that the quantification over paths naturally subsumes other
extensions of temporal logic with operators for information flow and knowledge.
The model checking problem for temporal logic with path quantification is
decidable. For alternation depth 1, the complexity is PSPACE in the length of
the formula and NLOGSPACE in the size of the system, as for linear-time
temporal logic
Universal inversion formulas for recovering a function from spherical means
The problem of reconstruction a function from spherical means is at the heart
of several modern imaging modalities and other applications. In this paper we
derive universal back-projection type reconstruction formulas for recovering a
function in arbitrary dimension from averages over spheres centered on the
boundary an arbitrarily shaped smooth convex domain. Provided that the unknown
function is supported inside that domain, the derived formulas recover the
unknown function up to an explicitly computed smoothing integral operator. For
elliptical domains the integral operator is shown to vanish and hence we
establish exact inversion formulas for recovering a function from spherical
means centered on the boundary of elliptical domains in arbitrary dimension.Comment: [20 pages, 2 figures] Compared to the previous versions I corrected
some typo
Exploration of Reaction Pathways and Chemical Transformation Networks
For the investigation of chemical reaction networks, the identification of
all relevant intermediates and elementary reactions is mandatory. Many
algorithmic approaches exist that perform explorations efficiently and
automatedly. These approaches differ in their application range, the level of
completeness of the exploration, as well as the amount of heuristics and human
intervention required. Here, we describe and compare the different approaches
based on these criteria. Future directions leveraging the strengths of chemical
heuristics, human interaction, and physical rigor are discussed.Comment: 48 pages, 4 figure
Continuous quantum measurement with independent detector cross-correlations
We investigate the advantages of using two independent, linear detectors for
continuous quantum measurement. For single-shot quantum measurement, the
measurement is maximally efficient if the detectors are twins. For weak
continuous measurement, cross-correlations allow a violation of the
Korotkov-Averin bound for the detector's signal-to-noise ratio. A vanishing
noise background provides a nontrivial test of ideal independent quantum
detectors. We further investigate the correlations of non-commuting operators,
and consider possible deviations from the independent detector model for
mesoscopic conductors coupled by the screened Coulomb interaction.Comment: 4 pages, 2 figure
Rectification of thermal fluctuations in a chaotic cavity heat engine
We investigate the rectification of thermal fluctuations in a mesoscopic
on-chip heat engine. The engine consists of a hot chaotic cavity capacitively
coupled to a cold cavity which rectifies the excess noise and generates a
directed current. The fluctuation-induced directed current depends on the
energy asymmetry of the transmissions of the contacts of the cold cavity to the
leads and is proportional to the temperature difference. We discuss the maximal
power output of the heat engine and its efficiency.Comment: Published version, 8 pages, 4 figure
Powerful energy harvester based on resonant-tunneling quantum wells
We analyze a heat engine based on a hot cavity connected via quantum wells to
electronic reservoirs. We discuss the output power as well as the efficiency
both in the linear and nonlinear regime. We find that the device delivers a
large power of about 0.18 W/cm^2 for a temperature difference of 1 K nearly
doubling the power than can be extracted from a similar heat engine based on
quantum dots. At the same time, the heat engine also has a good efficiency
although reduced from the quantum dot case. Due to the large level spacings
that can be achieved in quantum wells, our proposal opens the route towards
room-temperature applications of nanoscale heat engines.Comment: 13 pages, 4 figures, published versio
Heuristics-Guided Exploration of Reaction Mechanisms
For the investigation of chemical reaction networks, the efficient and
accurate determination of all relevant intermediates and elementary reactions
is mandatory. The complexity of such a network may grow rapidly, in particular
if reactive species are involved that might cause a myriad of side reactions.
Without automation, a complete investigation of complex reaction mechanisms is
tedious and possibly unfeasible. Therefore, only the expected dominant reaction
paths of a chemical reaction network (e.g., a catalytic cycle or an enzymatic
cascade) are usually explored in practice. Here, we present a computational
protocol that constructs such networks in a parallelized and automated manner.
Molecular structures of reactive complexes are generated based on heuristic
rules derived from conceptual electronic-structure theory and subsequently
optimized by quantum chemical methods to produce stable intermediates of an
emerging reaction network. Pairs of intermediates in this network that might be
related by an elementary reaction according to some structural similarity
measure are then automatically detected and subjected to an automated search
for the connecting transition state. The results are visualized as an
automatically generated network graph, from which a comprehensive picture of
the mechanism of a complex chemical process can be obtained that greatly
facilitates the analysis of the whole network. We apply our protocol to the
Schrock dinitrogen-fixation catalyst to study alternative pathways of catalytic
ammonia production.Comment: 27 pages, 9 figure
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