739 research outputs found
Integrated waveguides and deterministically positioned nitrogen vacancy centers in diamond created by femtosecond laser writing
Diamond's nitrogen vacancy (NV) center is an optically active defect with
long spin coherence times, showing great potential for both efficient nanoscale
magnetometry and quantum information processing schemes. Recently, both the
formation of buried 3D optical waveguides and high quality single NVs in
diamond were demonstrated using the versatile femtosecond laser-writing
technique. However, until now, combining these technologies has been an
outstanding challenge. In this work, we fabricate laser written photonic
waveguides in quantum grade diamond which are aligned to within micron
resolution to single laser-written NVs, enabling an integrated platform
providing deterministically positioned waveguide-coupled NVs. This fabrication
technology opens the way towards on-chip optical routing of single photons
between NVs and optically integrated spin-based sensing
Polarized micro-Raman studies of femtosecond laser written stress-induced optical waveguides in diamond
Understanding the physical mechanisms of the refractive index modulation
induced by femtosecond laser writing is crucial for tailoring the properties of
the resulting optical waveguides. In this work we apply polarized Raman
spectroscopy to study the origin of stress-induced waveguides in diamond,
produced by femtosecond laser writing. The change in the refractive index
induced by the femtosecond laser in the crystal is derived from the measured
stress in the waveguides. The results help to explain the waveguide
polarization sensitive guiding mechanism, as well as providing a technique for
their optimization.Comment: 5 pages, 4 figure
Indirect Regulation of Environmental Hazards Through the Provision of Information to The Public: The Case of SARA, Title III
Title III of the Superfund Amendments and Reauthorization Act of 1986 seeks to reduce the risks of chemical accidents through a strategy of indirect regulation that relies on providing the public with information about chemical hazards. For this strategy to be effective, citizens must aggressively utilize the information provided to monitor industrial practices and press for risk reduction. Since prior research suggests it is very difficult to evoke the degree of citizen action that would be required to make a strategy of indirect regulation successful, and since the federal legislation provided no funds for implementation, there is a question o/whether the structures set up by Title III are sufficient to achieve its objectives. This article reports the results of a national study that examined selected aspects of the implementation of Title III in an effort to assess the likely outcome of its attempt at indirect regulation. Our focus is on the degree to which the Title Ill-mandated Local Emergency Planning Committees are pursuing policies that are likely to get the necessary information to citizens and foster community debate on hazardous materials issues
Fabrication of quantum emitters in aluminium nitride by Al-ion implantation and thermal annealing
Single-photon emitters (SPEs) within wide-bandgap materials represent an
appealing platform for the development of single-photon sources operating at
room temperatures. Group III- nitrides have previously been shown to host
efficient SPEs which are attributed to deep energy levels within the large
bandgap of the material, in a way that is similar to extensively investigated
colour centres in diamond. Anti-bunched emission from defect centres within
gallium nitride (GaN) and aluminium nitride (AlN) have been recently
demonstrated. While such emitters are particularly interesting due to the
compatibility of III-nitrides with cleanroom processes, the nature of such
defects and the optimal conditions for forming them are not fully understood.
Here, we investigate Al implantation on a commercial AlN epilayer through
subsequent steps of thermal annealing and confocal microscopy measurements. We
observe a fluence-dependent increase in the density of the emitters, resulting
in creation of ensembles at the maximum implantation fluence. Annealing at 600
{\deg}C results in the optimal yield in SPEs formation at the maximum fluence,
while a significant reduction in SPE density is observed at lower fluences.
These findings suggest that the mechanism of vacancy formation plays a key role
in the creation of the emitters, and open new perspectives in the defect
engineering of SPEs in solid state.Comment: 11 pages, 7 figure
Underground railroads: citizen entitlements and unauthorized mobility in the antebellum period and today
In recent years, some scholars and prominent political figures have advocated the deepening of North American integration on roughly the European Union model, including the creation of new political institutions and the free movement of workers across borders. The construction of such a North American Union, if it included even a very thin trans-state citizenship regime, could represent the most significant expansion of individual entitlements in the region since citizenship was extended to former slaves in the United States. With such a possibility as its starting point, this article explores some striking parallels between the mass, legally prohibited movement across boundaries by fugitive slaves in the pre-Civil War period, and that by current unauthorized migrants to the United States. Both were, or are, met on their journeys by historically parallel groups of would-be helpers and hinderers. Their unauthorized movements in both periods serve as important signals of incomplete entitlements or institutional protections. Most crucially, moral arguments for extending fuller entitlements to both groups are shown here to be less distinct than may be prima facie evident, reinforcing the case for expanding and deepening the regional membership regime
Polarization study of single color centers in aluminum nitride
Color centers in wide-bandgap semiconductors are a promising class of solid-state quantum light source, many of which operate at room temperature. We examine a family of color centers in aluminum nitride, which emits close to 620 nm. We present a technique to rapidly map an ensemble of these single photon emitters, identifying all emitters, not just those with absorption dipole parallel to the laser polarization. We demonstrate a fast technique to determine their absorption polarization orientation in the c-plane, finding they are uniformly distributed in orientation, in contrast to many other emitters in crystalline materials
Coherent, mechanical control of a single electronic spin
The ability to control and manipulate spins via electrical, magnetic and
optical means has generated numerous applications in metrology and quantum
information science in recent years. A promising alternative method for spin
manipulation is the use of mechanical motion, where the oscillation of a
mechanical resonator can be magnetically coupled to a spins magnetic dipole,
which could enable scalable quantum information architectures9 and sensitive
nanoscale magnetometry. To date, however, only population control of spins has
been realized via classical motion of a mechanical resonator. Here, we
demonstrate coherent mechanical control of an individual spin under ambient
conditions using the driven motion of a mechanical resonator that is
magnetically coupled to the electronic spin of a single nitrogen-vacancy (NV)
color center in diamond. Coherent control of this hybrid mechanical/spin system
is achieved by synchronizing pulsed spin-addressing protocols (involving
optical and radiofrequency fields) to the motion of the driven oscillator,
which allows coherent mechanical manipulation of both the population and phase
of the spin via motion-induced Zeeman shifts of the NV spins energy. We
demonstrate applications of this coherent mechanical spin-control technique to
sensitive nanoscale scanning magnetometry.Comment: 6 pages, 4 figure
Ultra-bright and efficient single photon generation based on N-V centres in nanodiamonds on a solid immersion lens
Single photons are fundamental elements for quantum information technologies
such as quantum cryptography, quantum information storage and optical quantum
computing. Colour centres in diamond have proven to be stable single photon
sources and thus essential components for reliable and integrated quantum
information technology. A key requirement for such applications is a large
photon flux and a high efficiency. Paying tribute to various attempts to
maximise the single photon flux we show that collection efficiencies of photons
from colour centres can be increased with a rather simple experimental setup.
To do so we spin-coated nanodiamonds containing single nitrogen-vacancy colour
centres on the flat surface of a ZrO2 solid immersion lens. We found stable
single photon count rates of up to 853 kcts/s at saturation under continuous
wave excitation while having excess to more than 100 defect centres with count
rates from 400 kcts/s to 500 kcts/s. For a blinking defect centre we found
count rates up to 2.4 Mcts/s for time intervals of several ten seconds. It
seems to be a general feature that very high rates are accompanied by a
blinking behaviour. The overall collection efficiency of our setup of up to
4.2% is the highest yet reported for N-V defect centres in diamond. Under
pulsed excitation of a stable emitter of 10 MHz, 2.2% of all pulses caused a
click on the detector adding to 221 kcts/s thus opening the way towards diamond
based on-demand single photon sources for quantum applications
Fibrinogen is not elevated in the cerebrospinal fluid of patients with multiple sclerosis
<p>Abstract</p> <p>Background</p> <p>Elevated plasma fibrinogen levels are a well known finding in acute infectious diseases, acute stroke and myocardial infarction. However its role in the cerebrospinal fluid (CSF) of acute and chronic central (CNS) and peripheral nervous system (PNS) diseases is unclear.</p> <p>Findings</p> <p>We analyzed CSF and plasma fibrinogen levels together with routine parameters in patients with multiple sclerosis (MS), acute inflammatory diseases of the CNS (bacterial and viral meningoencephalitis, BM and VM) and PNS (Guillain-Barré syndrome; GBS), as well as in non-inflammatory neurological controls (OND) in a total of 103 patients. Additionally, MS patients underwent cerebral MRI scans at time of lumbar puncture.</p> <p>CSF and plasma fibrinogen levels were significantly lower in patients with MS and OND patients as compared to patients with BM, VM and GBS. There was a close correlation between fibrinogen levels and albumin quotient (rho = 0.769, <it>p </it>< 0.001) which strongly suggests passive transfer of fibrinogen through the blood-CSF-barrier during acute inflammation. Hence, in MS, the prototype of chronic neuroinflammation, CSF fibrinogen levels were not elevated and could not be correlated to clinical and neuroradiological outcome parameters.</p> <p>Conclusions</p> <p>Although previous work has shown clear evidence of the involvement of fibrinogen in MS pathogenesis, this is not accompanied by increased fibrinogen in the CSF compartment.</p
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