106 research outputs found
Practical fast gate rate InGaAs/InP single-photon avalanche photodiodes
We present a practical and easy-to-implement method for high-speed near
infrared single-photon detection based on InGaAs/InP single-photon avalanche
photodiodes (SPADs), combining aspects of both sine gating and
self-differencing techniques. At a gating frequency of 921 MHz and temperature
of -30 C we achieve: a detection efficiency of 9.3 %, a dark count
probability of 2.8 ns, while the afterpulse probability
is 1.6 ns, with a 10 ns "count-off time" setting. In
principle, the maximum count rate of the SPAD can approach 100 MHz, which can
significantly improve the performance for diverse applications.Comment: 3 pages and a few lines, 5 figures, 1 table. Accepted by Applied
Physics Letter
2.23 GHz gating InGaAs/InP single-photon avalanche diode for quantum key distribution
We implement an InGaAs/InP single-photon avalanche diode (SPAD) for
single-photon detection with the fastest gating frequency reported so far, of
2.23 GHz, which approaches the limit given by the bandwidth of the SPAD - 2.5
GHz. We propose a useful way to characterize the afterpulsing distribution for
rapid gating that allows for easy comparison with conventional gating regimes.
We compare the performance of this rapid gating scheme with free-running
detector and superconducting single-photon detector (SSPD) for the coherent
one-way quantum key distribution (QKD) protocol. The rapid gating system is
well suited for both high-rate and long-distance QKD applications, in which
Mbps key rates can be achieved for distances less than 40 km with 50 ns
deadtime and the maximum distance is limited to ~190km with 5 s deadtime.
These results illustrate that the afterpulsing is no longer a limiting factor
for QKD.Comment: 8 pages, 7 figures, submitted to Proceedings of SPI
Fast Single Photon Detectors and real-time Key Distillation: Enabling High Secret Key Rate QKD Systems
Quantum Key Distribution has made continuous progress over the last 20 years
and is now commercially available. However, the secret key rates (SKR) are
still limited to a few Mbps. Here, we present a custom multipixel
superconducting nanowire single-photon detectors and fast acquisition and
real-time key distillation electronics, removing two roadblocks and allowing an
increase of the SKR of more than an order of magnitude. In combination with a
simple 2.5 GHz clocked time-bin quantum key distribution system, we can
generate secret keys at a rate of 64 Mbps over a distance of 10.0 km and at a
rate of 3.0 Mbps over a distance of 102.4 km with real-time key distillation.Comment: 5 pages, 5 figures, submitted to Nature Photonic
Free Running Single Photon Detection based on a negative feedback InGaAs APD
InGaAs/InP-based semiconductor avalanche photodiode are usually employed for
single-photon counting at telecom wavelength. However they are affected by
afterpulsing which limits the diode performance. Recently, Princeton Lightwave
has commercialised a diode integrating monolithically a feedback resistor. This
solution effectively quenches the avalanche and drastically reduces
afterpulsing. Here, we report the development and characterization of a
detector module based on this diode, implementing an active hold-off circuit
which further reduces the afterpulsing and notably improves the detector
performances. We demonstrate free-running operation with 600 Hz dark count rate
at 10% detection efficiency. We also improved the standard double-window
technique for the afterpulsing characterization. Our algorithm implemented by a
FPGA allows to put the APD in a well-defined initial condition and to measure
the impact of the higher order afterpulses.Comment: 18 pages, 15 figures. Submitted to Journal of Modern Optic
Tracker fields from nonminimally coupled theory
We extend the concept of quintessence to a flat nonminimally coupled scalar -
tensor theories of gravity. By means of Noether's symmetries for the
cosmological pointlike Lagrangian L, it is possible to exhibit exact solutions
for a class of models depending on a free parameter s. This parameter comes out
in the relationship existing between the coupling F(\phi) and the potential
V(\phi) because of such a symmetry for L. When inverse power law potentials are
taken in account, a whole family of exact solutions parametrized by such an s
is proposed as a class of tracker fields, and some considerations are made
about them.Comment: 17 pages, submitted to Physical Review
Adopting sustainability competence-based education in academic disciplines : Insights from 13 higher education institutions
Higher Education Institutions (HEIs) have been incorporating sustainability into education and curricula, where recent research has focussed on sustainability competences, pedagogical approaches, and how to connect them, generally on a single HEI. The process of integrating sustainability into education based on curricula assessment has been explained using adoption of innovations; and has the potential to explain the process of developing competences through pedagogical approaches. The aim of this paper is to investigate this process at academic discipline level. An online survey was developed to investigate teaching sustainability competences in 13 HEIs, from which 678 responses from educators were obtained. The competences and pedagogical approaches from the responses were ranked, and then the connections between the competences and pedagogical approaches per discipline were analysed using a correlations-based framework, from which three disciplines groups were created. The groups were categorised using diffusion of innovations theory, which indicated that some disciplines are more innovative than others in adopting sustainability competence-based teaching. The results are used to propose two frameworks to better understand the adoption of sustainability competence-based teaching: (a) the D-RAPID framework; and (b) the Disciplinary Multi-dimensional Sustainability Influence Change for Academia (D-MuSICA) memework. The adoption of sustainability competence-base education must expand from a single HEI perspective to a disciplinary collaborative one spanning many HEIs, where academic disciplines should learn from each other's insights and mistakes and provide students with more transdisciplinary skillsets to make societies more sustainable.Peer reviewe
On Some Exponential Potentials for a Cosmological Scalar Field as Quintessence
We present general exact solutions for two classes of exponential potentials
in scalar field models for quintessence. The coupling is minimal and we
consider only dust and scalar field. To some extent, it is possible to
reproduce experimental results from supernovae.Comment: revised version. To appear Gen. Rel. Gra
Improving sustainability teaching by grouping and interrelating pedagogical approaches and sustainability competences: evidence from 15 worldwide higher education institutions
There has been increasing research on pedagogical approaches, sustainability competences, and how to connect them in Higher Education Institutions (HEIs). This paper's
aim is to provide deeper insights into the system of pedagogical approaches and sustainability competences, as well as how these interrelate. A survey was developed to investigate sustainability teaching in 15 HEIs. The survey was sent to educators of
each HEI from which 668 responses were obtained. The responses were analysed in a
five-step process: (1) descriptive statistics; (2) Pearson correlations; (3) principal component analyses (PCAs) to detect groups; (4) Pearson correlations between the groups; and
(5) regressions. The first step provided the base to carry out the PCAs, from which three
groups for the pedagogical approaches (Universal, Social, and Environmental) and three
for the sustainability competences (Extrospective-social, Introspective-personal, and
Cogitative-processual) were obtained. The correlations between the groups showed that:
(1) the competences are closely interrelated; (2) the pedagogical approaches are somehow interrelated; and (3) the pedagogical approaches are somehow interrelated to the
competences. The regressions showed that the Universal and Social groups would be
most suitable to develop all the competences' groups. The Environmental group develops
only the cogitative-processual competences' group. The results served as bases to propose the Sustainability Teaching System (STS), which provides deeper insights into the
system of pedagogical approaches and sustainability competences by grouping them, as
well as showing directionality and strength. To improve sustainability teaching, it is necessary to understand the pedagogical approaches' groups and how they can develop the
competences' groups.info:eu-repo/semantics/publishedVersio
On exact solutions for quintessential (inflationary) cosmological models with exponential potentials
We first study dark energy models with a minimally-coupled scalar field and
exponential potentials, admitting exact solutions for the cosmological
equations: actually, it turns out that for this class of potentials the
Einstein field equations exhibit alternative Lagrangians, and are completely
integrable and separable (i.e. it is possible to integrate the system
analytically, at least by quadratures). We analyze such solutions, especially
discussing when they are compatible with a late time quintessential expansion
of the universe. As a further issue, we discuss how such quintessential scalar
fields can be connected to the inflationary phase, building up, for this class
of potentials, a quintessential inflationary scenario: actually, it turns out
that the transition from inflation toward late-time exponential quintessential
tail admits a kination period, which is an indispensable ingredient of this
kind of theoretical models. All such considerations have also been done by
including radiation into the model.Comment: Revtex4, 10 figure
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