76 research outputs found
Spin resonance linewidths of bismuth donors in silicon coupled to planar microresonators
Ensembles of bismuth donor spins in silicon are promising storage elements
for microwave quantum memories due to their long coherence times which exceed
seconds. Operating an efficient quantum memory requires achieving critical
coupling between the spin ensemble and a suitable high-quality factor resonator
-- this in turn requires a thorough understanding of the lineshapes for the
relevant spin resonance transitions, particularly considering the influence of
the resonator itself on line broadening. Here, we present pulsed electron spin
resonance measurements of ensembles of bismuth donors in natural silicon, above
which niobium superconducting resonators have been patterned. By studying spin
transitions across a range of frequencies and fields we identify distinct line
broadening mechanisms, and in particular those which can be suppressed by
operating at magnetic-field-insensitive `clock transitions'. Given the donor
concentrations and resonator used here, we measure a cooperativity
and based on our findings we discuss a route to achieve unit cooperativity, as
required for a quantum memory
Random-access quantum memory using chirped pulse phase encoding
Quantum memories capable of faithfully storing and recalling quantum states
on-demand are powerful ingredients in bulding quantum networks
[arXiv:0806.4195] and quantum information processors [arXiv:1109.3743]. As in
conventional computing, key attributes of such memories are high storage
density and, crucially, random access, or the ability to read from or write to
an arbitrarily chosen register. However, achieving such random access with
quantum memories [arXiv:1904.09643] in a dense, hardware-efficient manner
remains a challenge, for example requiring dedicated cavities per qubit
[arXiv:1109.3743] or pulsed field gradients [arXiv:0908.0101]. Here we
introduce a protocol using chirped pulses to encode qubits within an ensemble
of quantum two-level systems, offering both random access and naturally
supporting dynamical decoupling to enhance the memory lifetime. We demonstrate
the protocol in the microwave regime using donor spins in silicon coupled to a
superconducting cavity, storing up to four multi-photon microwave pulses and
retrieving them on-demand up to 2~ms later. A further advantage is the natural
suppression of superradiant echo emission, which we show is critical when
approaching unit cooperativity. This approach offers the potential for
microwave random access quantum memories with lifetimes exceeding seconds
[arXiv:1301.6567, arXiv:2005.09275], while the chirped pulse phase encoding
could also be applied in the optical regime to enhance quantum repeaters and
networks
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Strain in heterogeneous quantum devices with atomic layer deposition
Abstract: We investigated the use of dielectric layers produced by atomic layer deposition (ALD) as an approach to strain mitigation in composite silicon/superconductor devices operating at cryogenic temperatures. We show that the addition of an ALD layer acts to reduce the strain of spins closest to silicon/superconductor interface where strain is highest. We show that appropriately biasing our devices at the hyperfine clock transition of bismuth donors in silicon, we can remove strain broadening and that the addition of ALD layers left T 2 (or temporal inhomogeneities) unchanged in these natural silicon devices
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Childhood trauma: methods for the identification of physeal fractures in non-adult skeletal remains
Objectives
Today, fractures at the growth plate (or physis) are common injuries in children, but provide challenges of identification in skeletonized remains. Clinical studies provide detailed information on the mechanisms, locations, age of occurrence, and complications associated with physeal fractures, enabling the development of new criteria for identifying this injury in non-adults. To test these criteria, skeletal remains from five rural and urban medieval cemeteries were examined.
Methods
The sample consisted of 961 skeletons (0-17 years) with open epiphyses. Macroscopic observation looked for any irregularities of the metaphysis or epiphysis which was consistent with the clinical appearance of physeal fractures or resulting complications. Radiographic examination was applied to identify fracture lines or early growth arrest.
Results
This study revealed 12 cases of physeal trauma (1.2%). Physeal fractures occurred predominantly at the distal end (75%), and while they were identified in all age categories, they were most frequent in those aged 12-17 years (0.2% TPR). The humerus was the most commonly affected location (3/12 or 25%).
Conclusions
This study highlights the potential for recognizing physeal fractures in children of all ages, enhancing our understanding of non-adult trauma, and enabling us to assign a more precise age of the injury to build up a picture of their activities in the past
The Maunakea Spectroscopic Explorer Book 2018
(Abridged) This is the Maunakea Spectroscopic Explorer 2018 book. It is
intended as a concise reference guide to all aspects of the scientific and
technical design of MSE, for the international astronomy and engineering
communities, and related agencies. The current version is a status report of
MSE's science goals and their practical implementation, following the System
Conceptual Design Review, held in January 2018. MSE is a planned 10-m class,
wide-field, optical and near-infrared facility, designed to enable
transformative science, while filling a critical missing gap in the emerging
international network of large-scale astronomical facilities. MSE is completely
dedicated to multi-object spectroscopy of samples of between thousands and
millions of astrophysical objects. It will lead the world in this arena, due to
its unique design capabilities: it will boast a large (11.25 m) aperture and
wide (1.52 sq. degree) field of view; it will have the capabilities to observe
at a wide range of spectral resolutions, from R2500 to R40,000, with massive
multiplexing (4332 spectra per exposure, with all spectral resolutions
available at all times), and an on-target observing efficiency of more than
80%. MSE will unveil the composition and dynamics of the faint Universe and is
designed to excel at precision studies of faint astrophysical phenomena. It
will also provide critical follow-up for multi-wavelength imaging surveys, such
as those of the Large Synoptic Survey Telescope, Gaia, Euclid, the Wide Field
Infrared Survey Telescope, the Square Kilometre Array, and the Next Generation
Very Large Array.Comment: 5 chapters, 160 pages, 107 figure
Disaster! A History of Earthquakes, Floods, Plagues, and Other Catastrophes20109 Disaster! A History of Earthquakes, Floods, Plagues, and Other Catastrophes
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Urban political culture in later-seventeenth-century England: York, 1649-1688.
This thesis is not available on this repository until the author agrees to make it public. If you are the author of this thesis and would like to make your work openly available, please contact us: [email protected] Library can supply a digital copy for private research purposes; interested parties should submit the request form here: http://www.lib.cam.ac.uk/collections/departments/digital-content-unit/ordering-imagesPlease note that print copies of theses may be available for consultation in the Cambridge University Library's Manuscript reading room. Admission details are at http://www.lib.cam.ac.uk/collections/departments/manuscripts-university-archive
The changing face of urinary continence surgery in England:a perspective from the Hospital Episode Statistics database
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