1,852 research outputs found
Distance measures to compare real and ideal quantum processes
With growing success in experimental implementations it is critical to
identify a "gold standard" for quantum information processing, a single measure
of distance that can be used to compare and contrast different experiments. We
enumerate a set of criteria such a distance measure must satisfy to be both
experimentally and theoretically meaningful. We then assess a wide range of
possible measures against these criteria, before making a recommendation as to
the best measures to use in characterizing quantum information processing.Comment: 15 pages; this version in line with published versio
Preparation and synthetic applications of Ă-alkoxystannanes as precursors to Ă-alkoxyorganolithiums
Higher Order Decompositions of Ordered Operator Exponentials
We present a decomposition scheme based on Lie-Trotter-Suzuki product
formulae to represent an ordered operator exponential as a product of ordinary
operator exponentials. We provide a rigorous proof that does not use a
time-displacement superoperator, and can be applied to non-analytic functions.
Our proof provides explicit bounds on the error and includes cases where the
functions are not infinitely differentiable. We show that Lie-Trotter-Suzuki
product formulae can still be used for functions that are not infinitely
differentiable, but that arbitrary order scaling may not be achieved.Comment: 16 pages, 1 figur
Information-theoretic equilibration: the appearance of irreversibility under complex quantum dynamics
The question of how irreversibility can emerge as a generic phenomena when
the underlying mechanical theory is reversible has been a long-standing
fundamental problem for both classical and quantum mechanics. We describe a
mechanism for the appearance of irreversibility that applies to coherent,
isolated systems in a pure quantum state. This equilibration mechanism requires
only an assumption of sufficiently complex internal dynamics and natural
information-theoretic constraints arising from the infeasibility of collecting
an astronomical amount of measurement data. Remarkably, we are able to prove
that irreversibility can be understood as typical without assuming decoherence
or restricting to coarse-grained observables, and hence occurs under distinct
conditions and time-scales than those implied by the usual decoherence point of
view. We illustrate the effect numerically in several model systems and prove
that the effect is typical under the standard random-matrix conjecture for
complex quantum systems.Comment: 15 pages, 7 figures. Discussion has been clarified and additional
numerical evidence for information theoretic equilibration is provided for a
variant of the Heisenberg model as well as one and two-dimensional random
local Hamiltonian
Embedded Monopoles
Using the embedded defect method, we classify the possible embeddings of a 't
Hooft-Polyakov monopole in a general gauge theory. We then discuss some
similarities with embedded vortices and relate our results to fundamental
monopoles.Comment: 6 pages, LaTe
Public Management on the Ground:Clustering Managers Based on Their Behavior
Public management research has identified a dizzying array of management variables that affect organizational performance. While scholars have learned much by analyzing one or a few specific behavioral dimensions of public management at a time, we argue for the value of a more holistic and inductive approach that uses data on several aspects of public management for identifying manager types. Such an approach accounts for both the cognitive processes of people affected by management and the reality that managersâ individual behavioral decisions are interrelated. We examine the overlap of 21 aspects of public school management behavior using cluster analysis. We identify four different manager types (âfirefighters,â âlaissez-faire managers,â âadministrators,â and âproactive floor managersâ), each reflecting a distinct constellation of managerial behaviors. The manager types we call âadministratorsâ and âproactive floor managersâ are associated with relatively better outcomes, while âfirefightersâ are associated with relatively worse outcomes
Testing general relativity using golden black-hole binaries
The coalescences of stellar-mass black-hole binaries through their inspiral,
merger, and ringdown are among the most promising sources for ground-based
gravitational-wave (GW) detectors. If a GW signal is observed with sufficient
signal-to-noise ratio, the masses and spins of the black holes can be estimated
from just the inspiral part of the signal. Using these estimates of the initial
parameters of the binary, the mass and spin of the final black hole can be
uniquely predicted making use of general-relativistic numerical simulations. In
addition, the mass and spin of the final black hole can be independently
estimated from the merger--ringdown part of the signal. If the binary black
hole dynamics is correctly described by general relativity (GR), these
independent estimates have to be consistent with each other. We present a
Bayesian implementation of such a test of general relativity, which allows us
to combine the constraints from multiple observations. Using kludge modified GR
waveforms, we demonstrate that this test can detect sufficiently large
deviations from GR, and outline the expected constraints from upcoming GW
observations using the second-generation of ground-based GW detectors.Comment: 5 pages, 2 fig
Extremum seeking control of quantum gates
To be useful for quantum computation, gate operations must be maintained at
high fidelities over long periods of time. In addition to decoherence, slow
drifts in control hardware leads to inaccurate gates, causing the quality of
operation of as-built quantum computers to vary over time. Here, we demonstrate
a data-driven approach to stabilized control, combining extremum-seeking
control (ESC) with direct randomized benchmarking (DRB) to stabilize two-qubit
gates under unknown control parameter fluctuations. As a case study, we
consider these control strategies in the context of a trapped ion quantum
computer using physically-realistic simulation. We then experimentally
demonstrate this control strategy on a state-of-the-art, commercial trapped-ion
quantum computer.Comment: 5 pages, 6 figure
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