50 research outputs found
Multidimensional cluster states using a single spin-photon interface coupled strongly to an intrinsic nuclear register
Photonic cluster states are a powerful resource for measurement-based quantum
computing and loss-tolerant quantum communication. Proposals to generate
multi-dimensional lattice cluster states have identified coupled spin-photon
interfaces, spin-ancilla systems, and optical feedback mechanisms as potential
schemes. Following these, we propose the generation of multi-dimensional
lattice cluster states using a single, efficient spin-photon interface coupled
strongly to a nuclear register. Our scheme makes use of the contact hyperfine
interaction to enable universal quantum gates between the interface spin and a
local nuclear register and funnels the resulting entanglement to photons via
the spin-photon interface. Among several quantum emitters, we identify the
silicon-29 vacancy centre in diamond, coupled to a nanophotonic structure, as
possessing the right combination of optical quality and spin coherence for this
scheme. We show numerically that using this system a 2x5-sized cluster state
with a lower-bound fidelity of 0.5 and repetition rate of 65 kHz is achievable
under currently realised experimental performances and with feasible technical
overhead. Realistic gate improvements put 100-photon cluster states within
experimental reach
Multi-tasking to Correct: Motion-Compensated MRI via Joint Reconstruction and Registration
This work addresses a central topic in Magnetic Resonance Imaging (MRI) which
is the motion-correction problem in a joint reconstruction and registration
framework. From a set of multiple MR acquisitions corrupted by motion, we aim
at - jointly - reconstructing a single motion-free corrected image and
retrieving the physiological dynamics through the deformation maps. To this
purpose, we propose a novel variational model. First, we introduce an
fidelity term, which intertwines reconstruction and registration along with the
weighted total variation. Second, we introduce an additional regulariser which
is based on the hyperelasticity principles to allow large and smooth
deformations. We demonstrate through numerical results that this combination
creates synergies in our complex variational approach resulting in higher
quality reconstructions and a good estimate of the breathing dynamics. We also
show that our joint model outperforms in terms of contrast, detail and blurring
artefacts, a sequential approach.Cambridge Cancer Centre, CMIH and CCIMI, University of Cambridge
A variational joint segmentation and registration framework for multimodal images
Image segmentation and registration are closely related image processing techniques and often required as simultaneous tasks. In this work, we introduce an optimization-based approach to a joint registration and segmentation model for multimodal images deformation. The model combines an active contour variational term with mutual information (MI) smoothing fitting term and solves in this way the difficulties of simultaneously performed segmentation and registration models for multimodal images. This combination takes into account the image structure boundaries and the movement of the objects, leading in this way to a robust dynamic scheme that links the object boundaries information that changes over time. Comparison of our model with state of art shows that our method leads to more consistent registrations and accurate results
Change and continuity in Japanese compensation practices: the case of occupational pensions since the early 2000s
This article analyses changes in the provision of Japanese occupational pensions since the early 2000s. It shows how Japanese companies have followed strategies of cost and risk reduction by creating multi-layered benefit systems that offer a combination of defined benefit (DB) and defined contribution (DC) plans whose benefits are becoming increasingly performance-oriented. Analysing the reasons behind the resilience of DB schemes in Japan, the article concludes that enterprise union behaviour has had less influence than regulatory issues and continued corporate commitment to long-standing employment practices for regular workers. These findings highlight the embeddedness of Japanese employment practices in their institutional context