pinecone/core-2020-05-10-deduplication huggingface dataset:
Tunable generation of entangled photons in a nonlinear directional
  coupler

The on-chip integration of quantum light sources has enabled the realization
of complex quantum photonic circuits. However, for the practical implementation
of such circuits in quantum information applications it is crucial to develop
sources delivering entangled quantum photon states with on-demand tunability.
Here we propose and experimentally demonstrate the concept of a widely tunable
quantum light source based on spontaneous parametric down-conversion in a
nonlinear directional coupler. We show that spatial photon-pair correlations
and entanglement can be reconfigured on-demand by tuning the phase difference
between the pump beams and the phase mismatch inside the structure. We
demonstrate the generation of split states, robust N00N states, various
intermediate regimes and biphoton steering. This fundamental scheme provides an
important advance towards the realization of reconfigurable quantum circuitry
Nonlinear switching and solitons in PT-symmetric photonic systems

One of the challenges of the modern photonics is to develop all-optical
devices enabling increased speed and energy efficiency for transmitting and
processing information on an optical chip. It is believed that the recently
suggested Parity-Time (PT) symmetric photonic systems with alternating regions
of gain and loss can bring novel functionalities. In such systems, losses are
as important as gain and, depending on the structural parameters, gain
compensates losses. Generally, PT systems demonstrate nontrivial
non-conservative wave interactions and phase transitions, which can be employed
for signal filtering and switching, opening new prospects for active control of
light. In this review, we discuss a broad range of problems involving nonlinear
PT-symmetric photonic systems with an intensity-dependent refractive index.
Nonlinearity in such PT symmetric systems provides a basis for many effects
such as the formation of localized modes, nonlinearly-induced PT-symmetry
breaking, and all-optical switching. Nonlinear PT-symmetric systems can serve
as powerful building blocks for the development of novel photonic devices
targeting an active light control.Comment: 33 pages, 33 figure
GaAs integrated quantum photonics : towards compact and multi-functional quantum photonic integrated circuits

We further acknowledge financial support from the European Commission within the FP7 project QUANTIP (Project No. 244026) and the Dutch Technology Foundation STW (Project No. 10380).The recent progress in integrated quantum optics has set the stage for the development of an integrated platform for quantum information processing with photons, with potential applications in quantum simulation. Among the different material platforms being investigated, direct-bandgap semiconductors and particularly gallium arsenide (GaAs) offer the widest range of functionalities, including single- and entangled-photon generation by radiative recombination, low-loss routing, electro-optic modulation and single-photon detection. This paper reviews the recent progress in the development of the key building blocks for GaAs quantum photonics and the perspectives for their full integration in a fully-functional and densely integrated quantum photonic circuit.PostprintPeer reviewe
Enhanced nonlinear effects in pulse propagation through epsilon-near-zero media

A.C. and C.R. acknowledge support from U.S. Army International Technology Center Atlantic for financial support (Grant No. W911NF-14-1-0315). A.D.F. acknowledges support from EPSRC (EP/I004602/1). D.F. acknowledges support from the European Research Council under the European Unions Seventh Framework Programme (FP/2007-2013)/ERC GA 306559.In recent years, unconventional metamaterial properties have triggered a revolution of electromagnetic research which has unveiled novel scenarios of wave-matter interaction. A very small dielectric permittivity is a leading example of such unusual features, since it produces an exotic static-like regime where the electromagnetic field is spatially slowly-varying over a physically large region. The so-called epsilon-near-zero metamaterials thus offer an ideal platform where to manipulate the inner details of the “stretched” field. Here we theoretically prove that a standard nonlinearity is able to operate such a manipulation to the point that even a thin slab produces a dramatic nonlinear pulse transformation, if the dielectric permittivity is very small within the field bandwidth. The predicted non-resonant releasing of full nonlinear coupling produced by the epsilon-near-zero condition does not resort to any field enhancement mechanism and opens novel routes to exploiting matter nonlinearity for steering the radiation by means of ultra-compact structures.PostprintPeer reviewe
$\mathcal{PT}$ symmetry in a fractional Schr\"odinger equation

We investigate the fractional Schr\"odinger equation with a periodic
$\mathcal{PT}$-symmetric potential. In the inverse space, the problem transfers
into a first-order nonlocal frequency-delay partial differential equation. We
show that at a critical point, the band structure becomes linear and symmetric
in the one-dimensional case, which results in a nondiffracting propagation and
conical diffraction of input beams. If only one channel in the periodic
potential is excited, adjacent channels become uniformly excited along the
propagation direction, which can be used to generate laser beams of high power
and narrow width. In the two-dimensional case, there appears conical
diffraction that depends on the competition between the fractional Laplacian
operator and the $\mathcal{PT}$-symmetric potential. This investigation may
find applications in novel on-chip optical devices.Comment: 8 pages, 4 figures; accepted by Laser & Photonics Review
Ultrafast all-optical order-to-chaos transition in silicon photonic crystal chips

ADF acknowledges support from EPSRC (EP/L017008/1).The interaction of light with nanostructured materials provides exciting new opportunities for investigating classical wave analogies of quantum phenomena. A topic of particular interest forms the interplay between wave physics and chaos in systems where a small perturbation can drive the behavior from the classical to chaotic regime. Here, we report an all-optical laser-driven transition from order to chaos in integrated chips on a silicon photonics platform. A square photonic crystal microcavity at telecom wavelengths is tuned from an ordered into a chaotic regime through a perturbation induced by ultrafast laser pulses in the ultraviolet range. The chaotic dynamics of weak probe pulses in the near infrared is characterized for different pump-probe delay times and at various positions in the cavity, with high spatial accuracy. Our experimental analysis, confirmed by numerical modelling based on random matrices, demonstrates that nonlinear optics can be used to control reversibly the chaotic behavior of light in optical resonators.PostprintPeer reviewe
Topological Phase Transitions and Thouless Pumping of Light in Photonic
  Waveguide Arrays

Photonic waveguide arrays provide an excellent platform for simulating
conventional topological systems, and they can also be employed for the study
of novel topological phases in photonics systems. However, a direct measurement
of bulk topological invariants remains a great challenge. Here we study
topological features of generalized commensurate Aubry-Andr\'{e}-Harper (AAH)
photonic waveguide arrays and construct a topological phase diagram by
calculating all bulk Chern numbers, and then explore the bulk-edge
correspondence by analyzing the topological edge states and their winding
numbers. In contrast to incommensurate AAH models, diagonal and off-diagonal
commensurate AAH models are not topologically equivalent. In particular, there
appear nontrivial topological phases with large Chern numbers and topological
phase transitions. By implementing Thouless pumping of light in photonic
waveguide arrays, we propose a simple scheme to measure the bulk Chern numbers.Comment: accepted for publication in Laser & Photonics Review
Sustained photon pulse revivals from inhomogeneously broadened spin
  ensembles

A very promising recent trend in applied quantum physics is to combine the
advantageous features of different quantum systems into what is called "hybrid
quantum technology". One of the key elements in this new field will have to be
a quantum memory enabling to store quanta over extended periods of time.
Systems that may fulfill the demands of such applications are comb-shaped spin
ensembles coupled to a cavity. Due to the decoherence induced by the
inhomogeneous ensemble broadening, the storage time of these quantum memories
is, however, still rather limited. Here we demonstrate how to overcome this
problem by burning well-placed holes into the spectral spin density leading to
spectacular performance in the multimode regime. Specifically, we show how an
initial excitation of the ensemble leads to the emission of more than a hundred
well-separated photon pulses with a decay rate significantly below the
fundamental limit of the recently proposed "cavity protection effect"
Enhancement of Terahertz Photoconductive Antennas and Photomixers
  Operation by Optical Nanoantennas

Photoconductive antennas and photomixers are very promising sources of
terahertz radiation that is widely used for spectroscopy, characterisation and
imaging of biological objects, deep space studies, scanning of surfaces and
detection of potentially hazardous substances. These antennas are compact and
allow generation of both ultrabroadband pulse and tunable continuous wave
terahertz signal at room temperatures, without a need of high-power optical
sources. However, such antennas have relatively low energy conversion
efficiency of femtosecond laser pulses or two close pump wavelengths
(photomixer) into the pulsed and continuous terahertz radiation,
correspondingly. Recently, an approach to solving this problem has been
proposed, that involves known methods of nanophotonics applied to terahertz
photoconductive antennas and photomixers. This approach comprises the use of
optical nanoantennas for enhancing the efficiency of pump laser radiation
absorption in the antenna gap, reducing the lifetime of photoexcited carriers,
and improving antenna thermal efficiency. This Review is intended to
systematise all the results obtained by researchers in this promising field of
hybrid optical-to-terahertz photoconductive antennas and photomixers
Separating Pathways in Double-Quantum Optical Spectroscopy Reveals
  Excitonic Interactions

Techniques for coherent multidimensional optical spectroscopy have been
developed and utilised to understand many different processes, including energy
transfer in photosynthesis and many-body effects in semiconductor
nanostructures. Double-quantum 2D spectroscopy is one variation that has been
particularly useful for understanding many-body effects. In condensed matter
systems, however, there are often many competing signal pathways, which can
make it difficult to isolate different contributions and retrieve quantitative
information. Here, a means of separating overlapping pathways while maintaining
the fidelity of the relevant peak/s is demonstrated. This selective approach is
used to isolate the double-quantum signal from a mixed two exciton state in a
semiconductor quantum well. The removal of overlapping peaks allows analysis of
the relevant peak-shape and thus details of interactions with the environment
and other carriers to be revealed. An alternative pulse ordering identifies a
double-quantum state associated only with GaAs defects, the signature of which
has previously been confused with other interaction induced effects. The
experimental approach described here provides access to otherwise hidden
details of excitonic interactions and demonstrates that the manner in which the
double-quantum coherence is generated can be important and provide an
additional control to help understand the many-body physics in complex systems
Optical Levitation of Nanodiamonds by Doughnut Beams in Vacuum

Optically levitated nanodiamonds with nitrogen-vacancy centers promise a
high-quality hybrid spin-optomechanical system. However, the trapped
nanodiamond absorbs energy form laser beams and causes thermal damage in
vacuum. We propose to solve the problem by trapping a composite particle (a
nanodiamond core coated with a less absorptive silica shell) at the center of
strongly focused doughnut-shaped laser beams. Systematical study on the
trapping stability, heat absorption, and oscillation frequency concludes that
the azimuthally polarized Gaussian beam and the linearly polarized
Laguerre-Gaussian beam ${\rm LG}_{03}$ are the optimal choices. With our
proposal, particles with strong absorption coefficients can be trapped without
obvious heating and, thus, the spin-optomechanical system based on levitated
nanodiamonds are made possible in high vacuum with the present experimental
techniques.Comment: 8 pages, 8 figure
Active demultiplexing of single-photons from a solid-state source

A scheme for active temporal-to-spatial demultiplexing of single-photons
generated by a solid-state source is introduced. The scheme scales
quasi-polynomially with photon number, providing a viable technological path
for routing n photons in the one temporal stream from a single emitter to n
different spatial modes. The active demultiplexing is demonstrated using a
state-of-the-art photon source---a quantum-dot deterministically coupled to a
micropillar cavity---and a custom-built demultiplexer---a network of
electro-optically reconfigurable waveguides monolithically integrated in a
lithium niobate chip. The measured demultiplexer performance can enable a
six-photon rate three orders of magnitude higher than the equivalent heralded
SPDC source, providing a platform for intermediate quantum computation
protocols.Comment: 4 pages, 2 figure
Highly tunable elastic dielectric metasurface lenses

Dielectric metasurfaces are two-dimensional structures composed of
nano-scatterers that manipulate phase and polarization of optical waves with
subwavelength spatial resolution, enabling ultra-thin components for free-space
optics. While high performance devices with various functionalities, including
some that are difficult to achieve using conventional optical setups have been
shown, most demonstrated components have a fixed functionality. Here we
demonstrate highly tunable metasurface devices based on subwavelength thick
silicon nano-posts encapsulated in a thin transparent elastic polymer. As proof
of concept, we demonstrate a metasurface microlens operating at 915 nm, with
focal distance tuning from 600 $\mu$m to 1400 $\mu$m through radial strain,
while maintaining a diffraction limited focus and a focusing efficiency above
50$\%$. The demonstrated tunable metasurface concept is highly versatile for
developing ultra-slim, multi-functional and tunable optical devices with
widespread applications ranging from consumer electronics to medical devices
and optical communications
Modulator-free coherent-one-way quantum key distribution

Time-bin encoding is an attractive method for transmitting photonic qubits
over long distances with minimal decoherence. It allows a simple receiver for
quantum key distribution (QKD) that extracts a key by measuring time of arrival
of photons and detects eavesdropping by measuring interference of pulses in
different time bins. In the past, coherent pulses have been generated using a
CW laser and an intensity modulator. A greatly simplified transmitter is
proposed and demonstrated here that works by directly modulating the laser
diode. Coherence between pulses is maintained by a weak seed laser. The
modulator-free source creates time-bin encoded pulses with a high extinction
ratio (29.4 dB) and an interference visibility above 97 %. The resulting QKD
transmitter gives estimated secure key rates up to 4.57 Mbit/s, the highest yet
reported for coherent-one-way QKD, and can be programmed for all protocols
using weak coherent pulses.Comment: 4 pages, 3 figure
Scattering invisibility with free-space field enhancement of
  all-dielectric nanoparticles

Simultaneous scattering invisibility and free-space field enhancement have
been achieved based on multipolar interferences among all-dielectric
nanoparticles. The scattering properties of all-dielectric nanowire quadrumers
are investigated and two sorts of scattering invisibilities have been
identified: the trivial invisibility where the individual nanowires are not
effectively excited; and the nontrivial invisibility with strong multipolar
excitations within each nanowire, which results in free-space field enhancement
outside the particles. It is revealed that such nontrivial invisibility
originates from not only the simultaneous excitations of both electric and
magnetic resonances, but also their significant magnetoelectric
cross-interactions. We further show that the invisibility obtained is both
polarization and direction selective, which can probably play a significant
role in various applications including non-invasive detection, sensing, and
non-disturbing medical diagnosis with high sensitivity and precision.Comment: 7 pages, 4 figures and comments are welcom
Dielectric nanoantenna as an efficient and ultracompact demultiplexer
  for surface waves

Nanoantennas for highly efficient excitation and manipulation of surface
waves at nanoscale are key elements of compact photonic circuits. However,
previously implemented designs employ plasmonic nanoantennas with high Ohmic
losses, relatively low spectral resolution, and complicated lithographically
made architectures. Here we propose an ultracompact and simple dielectric
nanoantenna (silicon nanosphere) allowing for both directional launching of
surface plasmon polaritons on a thin gold film and their demultiplexing with a
high spectral resolution. We show experimentally that mutual interference of
magnetic and electric dipole moments supported by the dielectric nanoantenna
results in opposite propagation of the excited surface waves whose wavelengths
differ by less than 50 nm in the optical range. Broadband reconfigurability of
the nanoantennas operational range is achieved simply by varying the diameter
of the silicon sphere. Moreover, despite subwavelength size ($<\lambda/3$) of
the proposed nanoantennas, they demonstrate highly efficient and directional
launching of surface waves both in the forward and backward directions with the
measured front-to-back ratio having a contrast of almost two orders of
magnitude within a 50 nm spectral band. Our lithography-free design has great
potential as highly efficient, low-cost, and ultracompact demultiplexer for
advanced photonic circuits.Comment: added relevant references; fixed typos in Supplementary eq. 8,9,1
Optical chirality from dark-field illumination of planar plasmonic
  nanostructures

Dark-field illumination is shown to make planar chiral nanoparticle
arrangements exhibit circular dichroism in extinction analogous to true chiral
scatterers. Circular dichrosim is experimentally observed at the maximum
scattering of single oligomers consisting rotationally symmetric arrangements
of gold nanorods, with strong agreement to numerical simulation. A dipole model
is developed to show that this effect is caused by a difference in the
geometric projection of a nanorod onto the handed orientation of electric
fields created by a circularly polarized dark-field that is normally incident
on a glass substrate. Owing to this geometric origin, the wavelength of the
peak chiral response is also experimentally shown to shift depending on the
separation between nanoparticles. All presented oligomers have physical
dimensions less than the operating wavelength, and the applicable extension to
closely packed planar arrays of oligomers is demonstrated to amplify the
magnitude of circular dichroism. The realization of strong chirality in these
oligomers demonstrates a new path to engineer optical chirality from planar
devices using dark-field illumination
The TRANSFoRm project: Experience and lessons learned regarding functional and interoperability requirements to support primary care

Introduction The current model of medical knowledge production, transfer, and application suffers from serious shortcomings. Learning health systems (LHS) have recently emerged as a potential solution—systems in which health information generated from patients is continuously analyzed to improve knowledge that will be transferred to patient care. Method Various approaches of data integration already exist and could be considered for the implementation of a LHS. We discuss what are the possible informatics approaches to address the functional requirements of LHS, in the specific context of primary care, and present the experience and lessons learned from the TRANSFoRm project. Result Implemented in 4 countries around 5 systems, TRANSFoRm is based on a local‐as‐view data mediation approach integrating the structural and terminological models in the same framework. It clearly demonstrated that it has the potential to address the requirements for a LHS in primary care, by dealing with data fragmented across multiple points of service. Also, it has the potential to support the generation of hypotheses from the context of clinical care, retrospective and prospective research, and decision support systems that improve the relevance of medical decisions. Conclusion The LHS approach embodies a shift from an institution‐centered to a patient‐centered perspective in knowledge production and transfer and can address important challenges in the primary care setting
Basics of EHL for practical application

10.04.15 KB. Ok to add accepted version to spiral, subject to 12 months embargo© 2014 in Wiley Online Library.Elastohydrodynamic lubrication (EHL) is present in all lubricated components whose elements roll together, including gears, rolling bearing, cams and constant velocity joints. These are characterised by having very localised and thus very high pressure contact, of order 1 to 3 GPa, between the elements. Two important practical properties of EHL contacts are the lubricant film thickness and the friction, and lubricant and machine designers and users need to be able to predict both of these. In principle, they can be determined from full numerical solution of the elastohydrodynamic problem. However, this is quite difficult and timeconsuming and requires detailed knowledge of the rheology of the lubricant film at high pressure and shear rate. This paper is aimed at practising engineers and describes alternative approaches, i.e. how EHL can be applied to predict film thickness and friction in practical applications
A combined analytical-experimental investigation of friction in cylinder liner inserts under mixed and boundary regimes of lubrication

This is an Open Access Article. It is published by Wiley under the Creative Commons Attribution 4.0 International Licence (CC BY). Full details of this licence are available at http://creativecommons.org/licenses/by/4.0It is necessary to develop an analytical solution in order to combine predictions with measured tribological parameters and fundamentally understand the mechanism of lubrication in a typical region of engine cycle, using tribometric studies. This paper deals with the development of such a representative approach. An analytical, rather than a numerical approach is expounded, as it is shown to sufﬁce for the purpose of precise time-efﬁcient predictions, which conform well to the measurements. The effect of surface topography, material and operating conditions are ascertained for the representative case of top compression ring—cylinder liner contact at the top dead centre reversal in transition from the compression to power stroke. Stainless steel uncoated surface used as press ﬁt cylinder liners for niche original equipment manufacturer applications are compared with those furnished with a Nickel-Silicon Carbide wear-resistant coating of choice in high performance motorsport