399 research outputs found
The diamond Nitrogen-Vacancy center as a probe of random fluctuations in a nuclear spin ensemble
New schemes that exploit the unique properties of Nitrogen-Vacancy (NV)
centers in diamond are presently being explored as a platform for
high-resolution magnetic sensing. Here we focus on the ability of a NV center
to monitor an adjacent mesoscopic nuclear spin bath. For this purpose, we
conduct comparative experiments where the NV spin evolves under the influence
of surrounding 13C nuclei or, alternatively, in the presence of asynchronous AC
fields engineered to emulate bath fluctuations. Our study reveals substantial
differences that underscore the limitations of the semi-classical picture when
interpreting and predicting the outcome of experiments designed to probe small
nuclear spin ensembles. In particular, our study elucidates the NV center
response to bath fluctuations under common pulse sequences, and explores a
detection protocol designed to probe time correlations of the nuclear spin bath
dynamics. Further, we show that the presence of macroscopic nuclear spin order
is key to the emergence of semi-classical spin magnetometry.Comment: 30 pages, 4 figure
Demonstration of Robust Quantum Gate Tomography via Randomized Benchmarking
Typical quantum gate tomography protocols struggle with a self-consistency
problem: the gate operation cannot be reconstructed without knowledge of the
initial state and final measurement, but such knowledge cannot be obtained
without well-characterized gates. A recently proposed technique, known as
randomized benchmarking tomography (RBT), sidesteps this self-consistency
problem by designing experiments to be insensitive to preparation and
measurement imperfections. We implement this proposal in a superconducting
qubit system, using a number of experimental improvements including
implementing each of the elements of the Clifford group in single `atomic'
pulses and custom control hardware to enable large overhead protocols. We show
a robust reconstruction of several single-qubit quantum gates, including a
unitary outside the Clifford group. We demonstrate that RBT yields physical
gate reconstructions that are consistent with fidelities obtained by randomized
benchmarking
Review article: the effects of antitumour necrosis factor-α on bone metabolism in inflammatory bowel disease.
BACKGROUND: Patients with inflammatory bowel disease (IBD) are at increased risk of osteoporosis. A number of studies have emerged in recent years indicating that tumour necrosis factor (TNF) blockade appears to have a beneficial effect on bone mineral density (BMD) in IBD patients.
AIMS: To provide a review of the available data regarding the effect of the currently licensed anti-TNF-α therapies on bone metabolism and BMD in IBD patients.
METHODS: A Medline search was performed using the search terms \u27infliximab\u27, \u27bone metabolism\u27, \u27IBD\u27, \u27BMD\u27, \u27bone markers\u27, \u27adalimumab\u27, \u27bone disease\u27, \u27Crohn\u27s disease\u27 and \u27ulcerative colitis\u27.
RESULTS: Infliximab has a beneficial effect on bone turnover markers in Crohn\u27s disease (CD) patients in the short term. The longest study to date comprising 24 CD patients showed an overall improvement in two bone formation markers - b-alkaline phosphatase (P = 0.022) and osteocalcin (P = 0.008) at 4 months post-treatment. Moreover, the largest study to date comprising 71 CD patients showed significant improvement in sCTx, a bone resorption marker (P = 0.04) at week-8 post-treatment. There is little data looking at the effect of anti-TNF-α therapy on bone metabolism in ulcerative colitis. Moreover, the long-term effects of anti-TNF-α therapy on bone structure and fracture risk in IBD patients are currently not known. The effect of cessation of anti-TNF-α therapy on bone metabolism is also unknown.
CONCLUSION: Properly controlled long-term trials are needed to fully evaluate the impact of TNF blockade on bone mineral density
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