2,890 research outputs found
Breathing dissipative solitons in optical microresonators
Dissipative solitons are self-localized structures resulting from a double
balance between dispersion and nonlinearity as well as dissipation and a
driving force. They occur in a wide variety of fields ranging from optics,
hydrodynamics to chemistry and biology. Recently, significant interest has
focused on their temporal realization in driven optical microresonators, known
as dissipative Kerr solitons. They provide access to coherent, chip-scale
optical frequency combs, which have already been employed in optical metrology,
data communication and spectroscopy. Such Kerr resonator systems can exhibit
numerous localized intracavity patterns and provide rich insights into
nonlinear dynamics. A particular class of solutions consists of breathing
dissipative solitons, representing pulses with oscillating amplitude and
duration, for which no comprehensive understanding has been presented to date.
Here, we observe and study single and multiple breathing dissipative solitons
in two different microresonator platforms: crystalline
resonator and integrated microring. We report a
deterministic route to access the breathing state, which allowed for a detailed
exploration of the breathing dynamics. In particular, we establish the link
between the breathing frequency and two system control parameters - effective
pump laser detuning and pump power. Using a fast detection, we present a direct
observation of the spatiotemporal dynamics of individual solitons, revealing
irregular oscillations and switching. An understanding of breathing solitons is
not only of fundamental interest concerning nonlinear systems close to critical
transition, but also relevant for applications to prevent breather-induced
instabilities in soliton-based frequency combs.Comment: 10 pages, 4 figure
Analogue models of classical and semiclassical gravity
Formal analogies between gravitational and acoustic or optical phenomena have been
a subject of study for over a century, leading to interesting scenarios for testing kinematic
aspects of general relativity in terrestrial laboratories. Here, some aspects about
analog models of gravity obtained from the description of these two different kind of systems
are analysed. First, light propagation in linear magnetoeletric media is examined.
In particular, it is shown that this effect produces mixed time-space terms in the effective
metric that depend only on the antisymmetric part of the generally non-symmetric magnetoelectric
coefficient. Furthermore, the dispersion relation related to the linear effect
motivates the analysis of an idealised exact model presenting an analog event horizon.
Then, a short discussion comparing different ways of constructing analog models is provided.
Subsequently, motivated by the results obtained in the optical context, we make a
bibliographic review about those analog models obtained from moving media, establishing
an equivalence between the propagation of acoustic perturbations in such a background
and the propagation of free scalar fields near a Schwarschild black hole. This last aspect
drives us to analyse the particle production in this scenario, a result that was first addressed
by Stephen Hawking [1, 2], which yields to the the description of the so called
Hawking radiation. When treating a non-stationary spacetime, particularly those presenting
a gravitational collapse, we can extend the description of quantum fields to curved
spacetimes by splitting the metric into two asymptotically stationary regions, with that
we show that the presence of the horizon is fundamental for the creation of particles. Finally,
it is also shown that the thermal distribution of this particle emission is identical to
the Planck distribution for bosons, and because of that the Hawking temperature appears
to be very small when we consider astrophysical scenarios
Detuning-dependent Properties and Dispersion-induced Instabilities of Temporal Dissipative Kerr Solitons in Optical Microresonators
Temporal-dissipative Kerr solitons are self-localized light pulses sustained
in driven nonlinear optical resonators. Their realization in microresonators
has enabled compact sources of coherent optical frequency combs as well as the
study of dissipative solitons. A key parameter of their dynamics is the
effective-detuning of the pump laser to the thermally- and Kerr-shifted cavity
resonance. Together with the free spectral range and dispersion, it governs the
soliton-pulse duration, as predicted by an approximate analytical solution of
the Lugiato-Lefever equation. Yet, a precise experimental verification of this
relation was lacking so far. Here, by measuring and controlling the
effective-detuning, we establish a new way of stabilizing solitons in
microresonators and demonstrate that the measured relation linking soliton
width and detuning deviates by less than 1 % from the approximate expression,
validating its excellent predictive power. Furthermore, a detuning-dependent
enhancement of specific comb lines is revealed, due to linear couplings between
mode-families. They cause deviations from the predicted comb power evolution,
and induce a detuning-dependent soliton recoil that modifies the pulse
repetition-rate, explaining its unexpected dependence on laser-detuning.
Finally, we observe that detuning-dependent mode-crossings can destabilize the
soliton, leading to an unpredicted soliton breathing regime (oscillations of
the pulse) that occurs in a normally-stable regime. Our results test the
approximate analytical solutions with an unprecedented degree of accuracy and
provide new insights into dissipative-soliton dynamics.Comment: Updated funding acknowledgement
Cesiumâvaporâbased delay of single photons emitted by deterministically fabricated quantum dot microlenses
Quantum light sources are key building blocks of photonic quantum technologies. For many applications, it is of interest to control the arrival time of single photons emitted by such quantum devices, or even to store single photons in quantum memories. In situ electron beam lithography is applied to realize InGaAs quantum dot (QD)âbased singleâphoton sources, which are interfaced with cesium (Cs) vapor to control the time delay of emitted photons. Via numerical simulations of the lightâmatter interaction in realistic QDâCsâvapor configurations, the influence of the vapor temperature and spectral QDâatom detuning is explored to maximize the achievable delay in experimental studies. As a result, this hybrid quantum system allows to trigger the emission of single photons with a linewidth as low as 1.54 GHz even under nonâresonant optical excitation and to delay the emission pulses by up to (15.71 ± 0.01) ns for an effective cell length of 150 mm. This work can pave the way for scalable quantum systems relying on a wellâcontrolled delay of single photons on a time scale of up to a few tens of nanoseconds.BMBF, 03V0630TIB, Entwicklung einer Halbleiterbasierten Einzelphotonenquelle fĂŒr die QuanteninformationstechnologieBMBF, 13N14876, Quantenkommunikations-Systeme auf Basis von Einzelphotonenquellen (QuSecure)DFG, 43659573, SFB 787: Halbleiter - Nanophotonik: Materialien, Modelle, BauelementeTU Berlin, Open-Access-Mittel - 201
Experienced Well-Being and Labor Market Status: The Role of Pleasure and Meaning
This paper examines the experienced well-being of employed and unemployed workers. We use the survey-adapted Day Reconstruction Method of the Innovation Sample of the German Socio-Economic Panel Study to analyze the role of the employment status for well-being, incorporating time use. We use the novel P-index to summarize the average share of pleasurable minutes on a day and show that in contrast to evaluative life satisfaction the unemployed experiences more pleasurable minutes due to the absence of working episodes. Hence, we examine working episodes in depth. While working is among the activities with the highest propensities for an unpleasant experience, it is also among the most meaningful activities. We show that meaning is a central non-monetary determinant for pleasure at work and find that pleasure during work and job satisfaction have a comparable association with meaning
Privacy at Risk: Exploiting Similarities in Health Data for Identity Inference
Smartwatches enable the efficient collection of health data that can be used
for research and comprehensive analysis to improve the health of individuals.
In addition to the analysis capabilities, ensuring privacy when handling health
data is a critical concern as the collection and analysis of such data become
pervasive. Since health data contains sensitive information, it should be
handled with responsibility and is therefore often treated anonymously.
However, also the data itself can be exploited to reveal information and break
anonymity. We propose a novel similarity-based re-identification attack on
time-series health data and thereby unveil a significant vulnerability. Despite
privacy measures that remove identifying information, our attack demonstrates
that a brief amount of various sensor data from a target individual is adequate
to possibly identify them within a database of other samples, solely based on
sensor-level similarities. In our example scenario, where data owners leverage
health data from smartwatches, findings show that we are able to correctly link
the target data in two out of three cases. User privacy is thus already
inherently threatened by the data itself and even when removing personal
information
Effect of ligand methylation on the spin-switching properties of surface-supported spin-crossover molecules
X-ray absorption spectroscopy investigations of the spin-state switching of spin-crossover (SCO) complexes adsorbed on a highly-oriented pyrolytic graphite (HOPG) surface have shown so far that HOPG is a promising candidate to realize applications such as spintronic devices because of the stability of SCO complexes on HOPG and the possibility of highly efficient thermal and light-induced spin-state switching. Herein, we present the spin switching of several Fe(II) SCO complexes adsorbed on an HOPG surface with particular emphasis on the thermally induced spin transition behaviour with respect to different structural modifications. The complexes of the type [Fe(bpz)2(L)] (bpzââ=ââdihydrobis(pyrazolyl)borate, Lââ=ââ1,10-phenanthroline, 2,2'-bipyridine) and their methylated derivatives exhibit SCO in the solid state with some differences regarding cooperative effects. However, in the vacuum-deposited thick films on quartz, complete and more gradual spin transition behavior is observable via UV/vis spectroscopy. In contrast to that, all complexes show large differences upon direct contact with HOPG. Whereas the unmodified complexes show thermal and light-induced SCO, the addition of e.g. two or four methyl groups leads to a partial or a complete loss of the SCO on the surface. The angle-dependent measurement of the N K-edge compared to calculations indicates that the complete SCO and HS-locked molecules on the surface exhibit a similar preferential orientation, whereas complexes undergoing an incomplete SCO exhibit a random orientation on the surface. These results are discussed in the light of molecule-substrate interactions
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