2,243 research outputs found
Four-photon orbital angular momentum entanglement
Quantum entanglement shared between more than two particles is essential to
foundational questions in quantum mechanics, and upcoming quantum information
technologies. So far, up to 14 two-dimensional qubits have been entangled, and
an open question remains if one can also demonstrate entanglement of
higher-dimensional discrete properties of more than two particles. A promising
route is the use of the photon orbital angular momentum (OAM), which enables
implementation of novel quantum information protocols, and the study of
fundamentally new quantum states. To date, only two of such multidimensional
particles have been entangled albeit with ever increasing dimensionality. Here
we use pulsed spontaneous parametric downconversion (SPDC) to produce photon
quadruplets that are entangled in their OAM, or transverse-mode degrees of
freedom; and witness genuine multipartite Dicke-type entanglement. Apart from
addressing foundational questions, this could find applications in quantum
metrology, imaging, and secret sharing.Comment: 5 pages, 4 figure
Sub-nanometer free electrons with topological charge
The holographic mask technique is used to create freely moving electrons with
quantized angular momentum. With electron optical elements they can be focused
to vortices with diameters below the nanometer range. The understanding of
these vortex beams is important for many applications. Here we present a theory
of focused free electron vortices. The agreement with experimental data is
excellent. As an immediate application, fundamental experimental parameters
like spherical aberration and partial coherence are determined.Comment: 4 pages, 5 figure
Dephasing of Mollow Triplet Sideband Emission of a Resonantly Driven Quantum Dot in a Microcavity
Detailed properties of resonance fluorescence from a single quantum dot in a
micropillar cavity are investigated, with particular focus on emission
coherence in dependence on optical driving field power and detuning.
Power-dependent series over a wide range could trace characteristic Mollow
triplet spectra with large Rabi splittings of GHz. In
particular, the effect of dephasing in terms of systematic spectral broadening
of the Mollow sidebands is observed as a strong fingerprint
of excitation-induced dephasing. Our results are in excellent agreement with
predictions of a recently presented model on phonon-dressed QD Mollow triplet
emission in the cavity-QED regime
Indistinguishable photons from the resonance fluorescence of a single quantum dot in a microcavity
We demonstrate purely resonant continuous-wave optical laser excitation to
coherently prepare an excitonic state of a single semiconductor quantum dot
(QDs) inside a high quality pillar microcavity. As a direct proof of QD
resonance fluorescence, the evolution from a single emission line to the
characteristic Mollow triplet10 is observed under increasing pump power. By
controlled utilization of weak coupling between the emitter and the fundamental
cavity mode through Purcell-enhancement of the radiative decay, a strong
suppression of pure dephasing is achieved, which reflects in close to Fourier
transform-limited and highly indistinguishable photons with a visibility
contrast of 90%. Our experiments reveal the model-like character of the coupled
QD-microcavity system as a promising source for the generation of ideal photons
at the quantum limit. From a technological perspective, the vertical cavity
symmetry -- with optional dynamic tunability -- provides strongly directed
light emission which appears very desirable for future integrated emitter
devices.Comment: 24 pages, 6 figure
Multi-dimensional laser spectroscopy of exciton-polaritons with spatial light modulators
We describe an experimental system that allows one to easily access the
dispersion curve of exciton-polaritons in a microcavity. Our approach is based
on two spatial light modulators (SLM), one for changing the excitation angles
(momenta), and the other for tuning the excitation wavelength. We show that
with this setup, an arbitrary number of states can be excited accurately and
that re-configuration of the excitation scheme can be done at high speed.Comment: 4 pages, 5 figure
Magnetic thermodynamics as proxy for chemical inhomogeneity in hemo-ilmenite solid solutions: A dynamic ac susceptibility study
In this study, we present ac susceptibility measurements for a synthetic and a natural hemo-ilmenite (HI) solid solution (x)FeTiO3-(1âx)Fe2O3 with compositions x=0.87(1) and 0.88(8), respectively. The focus of the investigation is the magnetic ordering at the Curie temperature T C and the spin-glass-like freezing at the freezing temperature T f. The sharpness of T C for the synthetic solid solution with well-defined structure indicates the chemical homogeneity of the solution, whereas the disperse magnetic ordering of the natural solid solution reveals inhomogeneities described as spin glass system ofvariations in composition x. The frequency dispersion of T f was determined between 10Hz and 10kHz and was found to obey a dynamic scaling power law. The relaxation rates deviate by five orders of magnitude where the synthetic solid solution exhibits Ï0=3(1)Ă104Hz and the natural one 5.5Ă109Hz. The strong deviation is attributed to the difference in the ordered state above T f. These findings provide an insight into the cooling-rate effects of natural solid solutions and how magnetic thermodynamics can be used to probe the chemical homogeneity of such system
Convective Excitation of Inertial Modes in Binary Neutron Star Mergers
We present the first very long-term simulations (extending up to ~140 ms
after merger) of binary neutron star mergers with piecewise polytropic
equations of state and in full general relativity. Our simulations reveal that
at a time of 30-50 ms after merger, parts of the star become convectively
unstable, which triggers the excitation of inertial modes. The excited inertial
modes are sustained up to several tens of milliseconds and are potentially
observable by the planned third-generation gravitational-wave detectors at
frequencies of a few kilohertz. Since inertial modes depend on the rotation
rate of the star and they are triggered by a convective instability in the
postmerger remnant, their detection in gravitational waves will provide a
unique opportunity to probe the rotational and thermal state of the merger
remnant. In addition, our findings have implications for the long-term
evolution and stability of binary neutron star remnantsComment: 6 pages, 4 figure
Collective Total Synthesis of Casbane Diterpenes: One Strategy, Multiple Targets
Of the more than 100 casbane diterpenes known to date, only the eponymous parent hydrocarbon casbene itself has ever been targeted by chemical synthesis. Outlined herein is a conceptually new approach that brings not a single but a variety of casbane derivatives into reach, especially the more highly oxygenated and arguably more relevant members of this family. The key design elements are a catalystâcontrolled intramolecular cyclopropanation with or without subsequent equilibration, chain extension of the resulting stereoisomeric cyclopropane building blocks by chemoselective hydroboration/crossâcoupling, and the efficient closure of the strained macrobicyclic framework by ringâclosing alkyne metathesis. A hydroxyâdirected catalytic transâhydrostannation allows for lateâstage diversity. These virtues are manifested in the concise total syntheses of depressin, yuexiandajisuâ
A, and entâpekineninâ
C. The last compound turned out to be identical to euphorhylonalâ
A, the structure of which had clearly been misassigned
Spontaneously Localized Photonic Modes Due to Disorder in the Dielectric Constant
We present the first experimental evidence for the existence of strongly
localized photonic modes due to random two dimensional fluctuations in the
dielectric constant. In one direction, the modes are trapped by ordered Bragg
reflecting mirrors of a planar, one wavelength long, microcavity. In the cavity
plane, they are localized by disorder, which is due to randomness in the
position, composition and sizes of quantum dots located in the anti-node of the
cavity. We extend the theory of disorder induced strong localization of
electron states to optical modes and obtain quantitative agreement with the
main experimental observations.Comment: 6 page
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