755 research outputs found
Initial steps towards automatic segmentation of the wire frame of stent grafts in CT data
For the purpose of obtaining a geometrical model of the wire frame of stent grafts, we propose three tracking methods to segment the stent's wire, and compare them in an experiment. A 2D test image was created by obtaining a projection of a 3D volume containing a stent. The image was modified to connect the parts of the stent's frame and thus create a single path. Ten versions of this image were obtained by adding different noise realizations. Each algorithm was started at the start of each of the ten images, after which the traveled paths were compared to the known correct path to determine the performance. Additionally, the algorithms were applied to 3D clinical data and visually inspected. The method based on the minimum cost path algorithm scored excellent in the experiment and showed good results on the 3D data. Future research will focus on establishing a geometrical model by determining the corner points and the crossings from the results of this method.\u
Simulability of Imperfect Gaussian and Superposition Boson Sampling
We study the hardness of classically simulating Gaussian boson sampling at
nonzero photon distinguishability. We find that similar to regular boson
sampling, distinguishability causes exponential attenuation of the many-photon
interference terms in Gaussian boson sampling. Barring an open problem in the
theory of matrix permanents, this leads to an efficient classical algorithm to
simulate Gaussian boson sampling in the presence of distinguishability. We also
study a new form of boson sampling based on photon number superposition states,
for which we also show noise sensivity. The fact that such superposition boson
sampling is not simulable with out method at zero distinguishability is the
first evidence for the computational hardness of this problem
Marginal probabilities in boson samplers with arbitrary input states
With the recent claim of a quantum advantage demonstration in photonics by
Zhong et al, the question of the computation of lower-order approximations of
boson sampling with arbitrary quantum states at arbitrary distinguishability
has come to the fore. In this work, we present results in this direction,
building on the results of Clifford and Clifford. In particular, we show:
1) How to compute marginal detection probabilities (i.e. probabilities of the
detection of some but not all photons) for arbitrary quantum states.
2) Using the first result, how to generalize the sampling algorithm of
Clifford and Clifford to arbitrary photon distinguishabilities and arbitrary
input quantum states.
3) How to incorporate truncations of the quantum interference into a sampling
algorithm.
4) A remark considering maximum likelihood verification of the recent
photonic quantum advantage experiment
Quantum noise limited and entanglement-assisted magnetometry
We study experimentally the fundamental limits of sensitivity of an atomic
radio-frequency magnetometer. First we apply an optimal sequence of state
preparation, evolution, and the back-action evading measurement to achieve a
nearly projection noise limited sensitivity. We furthermore experimentally
demonstrate that Einstein-Podolsky-Rosen (EPR) entanglement of atoms generated
by a measurement enhances the sensitivity to pulsed magnetic fields. We
demonstrate this quantum limited sensing in a magnetometer utilizing a truly
macroscopic ensemble of 1.5*10^12 atoms which allows us to achieve
sub-femtoTesla/sqrt(Hz) sensitivity.Comment: To appear in Physical Review Letters, April 9 issue (provisionally
Benchmarking of Gaussian boson sampling using two-point correlators
Gaussian boson sampling is a promising scheme for demonstrating a quantum
computational advantage using photonic states that are accessible in a
laboratory and, thus, offer scalable sources of quantum light. In this
contribution, we study two-point photon-number correlation functions to gain
insight into the interference of Gaussian states in optical networks. We
investigate the characteristic features of statistical signatures which enable
us to distinguish classical from quantum interference. In contrast to the
typical implementation of boson sampling, we find additional contributions to
the correlators under study which stem from the phase dependence of Gaussian
states and which are not observable when Fock states interfere. Using the first
three moments, we formulate the tools required to experimentally observe
signatures of quantum interference of Gaussian states using two outputs only.
By considering the current architectural limitations in realistic experiments,
we further show that a statistically significant discrimination between quantum
and classical interference is possible even in the presence of loss, noise, and
a finite photon-number resolution. Therefore, we formulate and apply a
theoretical framework to benchmark the quantum features of Gaussian boson
sampling under realistic conditions
Gaussian Optical Ising Machines
It has recently been shown that optical parametric oscillator (OPO) Ising
machines, consisting of coupled optical pulses circulating in a cavity with
parametric gain, can be used to probabilistically find low-energy states of
Ising spin systems. In this work, we study optical Ising machines that operate
under simplified Gaussian dynamics. We show that these dynamics are sufficient
for reaching probabilities of success comparable to previous work. Based on
this result, we propose modified optical Ising machines with simpler designs
that do not use parametric gain yet achieve similar performance, thus
suggesting a route to building much larger systems.Comment: 6 page
Will I Make It On My Own? Voices and Visions of 17-Year-Old Youth in Transition
Voices and Visions of Youth in Transition, a longitudinal transformative youth-centered research study, examines the experiences and thoughts of youth as they transition out of foster care at the ages of 17, 19, and 21. Qualitative and quantitative survey inquiries were used to attain an understanding of the experiences of 198 youth in foster care who were 17 years old during the first wave of data collection. Nine critical areas related to the transition out of foster care were examined: education; employment; housing; high-risk behavior; access to health insurance; social connections with adults, family, and friends; the transition plan; transition concerns; and personal goals. The majority of youth reported the importance of resources, social support, and personal habits and skills as they prepare for the transition out of foster care. Youth also expressed concerns about being on their own without adequate support and not being able to make it on their own. This article highlights the study's findings from the first wave of data collection and how youth in transition are meaningfully engaged and empowered throughout the research process
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