154 research outputs found
Urban wireless traffic evolution: the role of new devices and the effect of policy
The emergence of new wireless technologies, such as the Internet of Things,
allows digitalizing new and diverse urban activities. Thus, wireless traffic
grows in volume and complexity, making prediction, investment planning, and
regulation increasingly difficult. This article characterizes urban wireless
traffic evolution, supporting operators to drive mobile network evolution and
policymakers to increase national and local competitiveness. We propose a
holistic method that widens previous research scope, including new devices and
the effect of policy from multiple government levels. We provide an analytical
formulation that combines existing complementary methods on traffic evolution
research and diverse data sources. Results for a centric area of Helsinki
during 2020-2030 indicate that daily volumes increase, albeit a surprisingly
large part of the traffic continues to be generated by smartphones. Machine
traffic gains importance, driven by surveillance video cameras and connected
cars. While camera traffic is sensitive to law enforcement policies and data
regulation, car traffic is less affected by transport electrification policy.
High-priority traffic remains small, even under encouraging autonomous vehicle
policies. We suggest that 5G small cells might be needed around 2025, albeit
the utilization of novel radio technology and additional mid-band spectrum
could delay this need until 2029. We argue that mobile network operators
inevitably need to cooperate in constructing a single, shared small cell
network to mitigate the high deployment costs of massively deploying small
cells. We also provide guidance to local and national policymakers for
IoT-enabled competitive gains via the mitigation of five bottlenecks. For
example, local monopolies for mmWave connectivity should be facilitated on
space-limited urban furniture or risk an eventual capacity crunch, slowing down
digitalization
Measurement and Control of Single Nitrogen-Vacancy Center Spins above 600 K
We study the spin and orbital dynamics of single nitrogen-vacancy (NV)
centers in diamond between room temperature and 700 K. We find that the ability
to optically address and coherently control single spins above room temperature
is limited by nonradiative processes that quench the NV center's
fluorescence-based spin readout between 550 and 700 K. Combined with electronic
structure calculations, our measurements indicate that the energy difference
between the 3E and 1A1 electronic states is approximately 0.8 eV. We also
demonstrate that the inhomogeneous spin lifetime (T2*) is temperature
independent up to at least 625 K, suggesting that single NV centers could be
applied as nanoscale thermometers over a broad temperature range.Comment: 8 pages, 5 figures, and 14 pages of supplemental material with
additional figures. Title change and minor revisions from previous version.
DMT and DJC contributed equally to this wor
Resonance fluorescence from an artificial atom in squeezed vacuum
We present an experimental realization of resonance fluorescence in squeezed
vacuum. We strongly couple microwave-frequency squeezed light to a
superconducting artificial atom and detect the resulting fluorescence with high
resolution enabled by a broadband traveling-wave parametric amplifier. We
investigate the fluorescence spectra in the weak and strong driving regimes,
observing up to 3.1 dB of reduction of the fluorescence linewidth below the
ordinary vacuum level and a dramatic dependence of the Mollow triplet spectrum
on the relative phase of the driving and squeezed vacuum fields. Our results
are in excellent agreement with predictions for spectra produced by a two-level
atom in squeezed vacuum [Phys. Rev. Lett. \textbf{58}, 2539-2542 (1987)],
demonstrating that resonance fluorescence offers a resource-efficient means to
characterize squeezing in cryogenic environments
Engineering shallow spins in diamond with nitrogen delta-doping
We demonstrate nanometer-precision depth control of nitrogen-vacancy (NV)
center creation near the surface of synthetic diamond using an in situ nitrogen
delta-doping technique during plasma-enhanced chemical vapor deposition.
Despite their proximity to the surface, doped NV centers with depths (d)
ranging from 5 - 100 nm display long spin coherence times, T2 > 100 \mus at d =
5 nm and T2 > 600 \mus at d \geq 50 nm. The consistently long spin coherence
observed in such shallow NV centers enables applications such as atomic-scale
external spin sensing and hybrid quantum architectures.Comment: 14 pages, 4 figures, 11 pages of additional supplementary materia
Terminology for describing normally sited and ectopic pregnancies on ultrasound : eSHRE recommendations for good practice
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