5,195 research outputs found
Quantum Walks with Entangled Coins
We present a mathematical formalism for the description of unrestricted
quantum walks with entangled coins and one walker. The numerical behaviour of
such walks is examined when using a Bell state as the initial coin state, two
different coin operators, two different shift operators, and one walker. We
compare and contrast the performance of these quantum walks with that of a
classical random walk consisting of one walker and two maximally correlated
coins as well as quantum walks with coins sharing different degrees of
entanglement.
We illustrate that the behaviour of our walk with entangled coins can be very
different in comparison to the usual quantum walk with a single coin. We also
demonstrate that simply by changing the shift operator, we can generate widely
different distributions. We also compare the behaviour of quantum walks with
maximally entangled coins with that of quantum walks with non-entangled coins.
Finally, we show that the use of different shift operators on 2 and 3 qubit
coins leads to different position probability distributions in 1 and 2
dimensional graphs.Comment: Two new sections and several changes from referees' comments. 12
pages and 12 (colour) figure
Mass fractionation of the lunar surface by solar wind sputtering
The sputtering of the lunar surface by the solar wind is examined as a possible mechanism of mass fractionation. Simple arguments based on current theories of sputtering and the ballistics of the sputtered atoms suggest that most ejected atoms will have sufficiently high energy to escape lunar gravity. However, the fraction of atoms which falls back to the surface is enriched in the heavier atomic components relative to the lighter ones. This material is incorporated into the heavily radiation-damaged outer surfaces of grains where it is subject to resputtering. Over the course of several hundred years an equilibrium surface layer, enriched in heavier atoms, is found to form. The dependence of the calculated results upon the sputtering rate and on the details of the energy spectrum of sputtered particles is investigated. It is concluded that mass fractionation by solar wind sputtering is likely to be an important phenomenon on the lunar surface
Separable Structure of Many-Body Ground-State Wave Function
We have investigated a general structure of the ground-state wave function
for the Schr\"odinger equation for identical interacting particles (bosons
or fermions) confined in a harmonic anisotropic trap in the limit of large .
It is shown that the ground-state wave function can be written in a separable
form. As an example of its applications, this form is used to obtain the
ground-state wave function describing collective dynamics for trapped
bosons interacting via contact forces.Comment: J. Phys. B: At. Mol. Opt. Phys. 33 (2000) (accepted for publication
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Integrating rich user feedback into intelligent user interfaces
The potential for machine learning systems to improve via a mutually beneficial exchange of information with users has yet to be explored in much detail. Previously, we found that users were willing to provide a generous amount of rich feedback to machine learning systems, and that the types of some of this rich feedback seem promising for assimilation by machine learning algorithms. Following up on those findings, we ran an experiment to assess the viability of incorporating real-time keyword-based feedback in initial training phases when data is limited. We found that rich feedback improved accuracy but an initial unstable period often caused large fluctuations in classifier behavior. Participants were able to give feedback by relying heavily on system communication in order to respond to changes. The results show that in order to benefit from the user’s knowledge, machine learning systems must be able to absorb keyword-based rich feedback in a graceful manner and provide clear explanations of their predictions
Non-Analytic Vertex Renormalization of a Bose Gas at Finite Temperature
We derive the flow equations for the symmetry unbroken phase of a dilute
3-dimensional Bose gas. We point out that the flow equation for the interaction
contains parts which are non-analytic at the origin of the frequency-momentum
space. We examine the way this non-analyticity affects the fixed point of the
system of the flow equations and shifts the value of the critical exponent for
the correlation length closer to the experimental result in comparison with
previous work where the non-analyticity was neglected. Finally, we emphasize
the purely thermal nature of this non-analytic behaviour comparing our approach
to a previous work where non-analyticity was studied in the context of
renormalization at zero temperature.Comment: 21 pages, 4 figure
Photosynthesis in Corn
Studies on the photosynthetic efficiency of corn conducted in the Department of Botany at Ames have several indications
Conference Scheduling Undermines Diversity Efforts
We assessed diversity-focused programming at 29 major biology conferences from 2010 to 2019, noting events tailored to three underrepresented and marginalized groups in biology: women, ethnic and racial minority groups, and the LGBTQ+ community (see Supplementary Information for further methods). Since 2010, diversity-focused events have become more common but frequently address only a subset of URG communities. In general, the percentage of conferences with diversity-focused events increased from 75% in 2019. On average, women were the most frequent focus of these events and the LGBTQ+ community was the least frequent focus (Fig. 1a)
Limitations of light delay and storage times in EIT experiments with condensates
We investigate the limitations arising from atomic collisions on the storage
and delay times of probe pulses in EIT experiments. We find that the atomic
collisions can be described by an effective decay rate that limits storage and
delay times. We calculate the momentum and temperature dependence of the decay
rate and find that it is necessary to excite atoms at a particular momentum
depending on temperature and spacing of the energy levels involved in order to
minimize the decoherence effects of atomic collisions.Comment: 4 pages RevTeX, 4 figures. Send correspondence to
[email protected]
Just how long can you live in a black hole and what can be done about it?
We study the problem of how long a journey within a black hole can last.
Based on our observations, we make two conjectures. First, for observers that
have entered a black hole from an asymptotic region, we conjecture that the
length of their journey within is bounded by a multiple of the future
asymptotic ``size'' of the black hole, provided the spacetime is globally
hyperbolic and satisfies the dominant-energy and non-negative-pressures
conditions. Second, for spacetimes with Cauchy surfaces (or an
appropriate generalization thereof) and satisfying the dominant energy and
non-negative-pressures conditions, we conjecture that the length of a journey
anywhere within a black hole is again bounded, although here the bound requires
a knowledge of the initial data for the gravitational field on a Cauchy
surface. We prove these conjectures in the spherically symmetric case. We also
prove that there is an upper bound on the lifetimes of observers lying ``deep
within'' a black hole, provided the spacetime satisfies the
timelike-convergence condition and possesses a maximal Cauchy surface. Further,
we investigate whether one can increase the lifetime of an observer that has
entered a black hole, e.g., by throwing additional matter into the hole.
Lastly, in an appendix, we prove that the surface area of the event horizon
of a black hole in a spherically symmetric spacetime with ADM mass
is always bounded by , provided
that future null infinity is complete and the spacetime is globally hyperbolic
and satisfies the dominant-energy condition.Comment: 20 pages, REVTeX 3.0, 6 figures included, self-unpackin
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