arXiv subjects

C. Schneider

Publications and source records attributed to C. Schneider.

At least 55 records · Page 3Linked to original sources

arXiv2021

Quantum interference between independent solid-state single-photon sources separated by 300 km fiber

In the quest to realize a scalable quantum network, semiconductor quantum dots (QDs) offer distinct advantages including high single-photon efficiency and indistinguishability, high repetition rate (tens of GHz with Purcell enhancement), interconnectivity with spin qubits, and a scalable on-chip platform. However, in the past two decades, the visibility of quantum interference between independent QDs rarely went beyond the classical limit of 50$\%$ and the distances were limited from a few meters to kilometers. Here, we report quantum interference between two single photons from independent QDs separated by 302 km optical fiber. The single photons are generated from resonantly driven single QDs deterministically coupled to microcavities. Quantum frequency conversions are used to eliminate the QD inhomogeneity and shift the emission wavelength to the telecommunication band. The observed interference visibility is 0.67$\pm$0.02 (0.93$\pm$0.04) without (with) temporal filtering. Feasible improvements can further extend the distance to 600 km. Our work represents a key step to long-distance solid-state quantum networks.

quant-ph↗

arXiv2021

The corona -- chromosphere connection studied with simultaneous eROSITA and TIGRE observations

Stellar activity is inherently time variable, therefore simultaneous measurements are necessary to study the correlation between different activity indicators. In this study we compare X-ray fluxes measured within the first all-sky survey conducted by the extended ROentgen Survey with an Imaging Telescope Array (eROSITA) instrument on board the Spectrum-Roentgen-Gamma (SRG) observatory to Ca II H & K, excess flux measurements R+, using observations made with the robotic TIGRE telescope. We created the largest sample of simultaneous X-ray and spectroscopic Ca II H & K observations of late-type stars obtained so far, and in addition, previous measurements of Ca II H & K for all sample stars were obtained. We find the expected correlation between our log(L_X/L_bol) to log(R+) measurements, but when the whole stellar ensemble is considered, the correlation between coronal and chromospheric activity indicators does not improve when the simultaneously measured data are used. A more detailed analysis shows that the correlation of log(L_X/L_bol) to log(R+) measurements of the pseudo-simultaneous data still has a high probability of being better than that of a random set of non-simultaneous measurements with a long time baseline between the observations. Cyclic variations on longer timescales are therefore far more important for the activity flux-flux relations than short-term variations in the form of rotational modulation or flares, regarding the addition of "noise" to the activity flux-flux correlations. Finally, regarding the question of predictability of necessarily space-based log(L_X/L_bol) measurements by using ground-based chromospheric indices, we present a relation for estimating log(L_X/L_bol) from R+ values and show that the expected error in the calculated minus observed (C-O) log(L_X/L_bol) values is 0.35 dex.

astro-ph.SR↗

arXiv2021

Intrinsic circularly-polarized exciton emission in a twisted van-der-Waals heterostructure

The investigation of excitons in van-der-Waals heterostructures has led to profound insights into the interplay of crystal symmetries and fundamental effects of light-matter coupling. In particular, the polarization selection rules in undistorted, slightly twisted heterostructures of MoSe$_2$/WSe$_2$ were found to be connected with the Moiré superlattice. Here, we report the emergence of a significant degree of circular polarization of excitons in such a hetero-structure upon non-resonant driving with a linearly polarized laser. The effect is present at zero magnetic field, and sensibly reacts on perpendicularly applied magnetic field. The giant magnitude of polarization, which cannot be explained by conventional birefringence or optical activity of the twisted lattice, suggests a kinematic origin arising from an emergent pyromagnetic symmetry in our structure, which we exploit to gain insight into the microscopic processes of our device.

cond-mat.mes-hall↗

arXiv2021

The Logarithmic Contributions to the Polarized and Operator Matrix Elements in Deeply Inelastic Scattering

We compute the logarithmic contributions to the polarized massive Wilson coefficients for deep-inelastic scattering in the asymptotic region $Q^2 \gg m^2$ to 3-loop order in the fixed-flavor number scheme and present the corresponding expressions for the polarized massive operator matrix elements needed in the variable flavor number scheme. The calculation is performed in the Larin scheme. For the massive operator matrix elements $A_{qq,Q}^{(3),\rm PS}$ and $A_{qg,Q}^{(3),\rm S}$ the complete results are presented. The expressions are given in Mellin-$N$ space and in momentum fraction $z$-space.

hep-ph↗

arXiv2021

A Two-Kind-Boson Mixture Honeycomb Hamiltonian of Bloch Exciton-Polaritons

The electronic bandstructure of a solid is a collection of allowed bands separated by forbidden bands, revealing the geometric symmetry of the crystal structures. Comprehensive knowledge of the bandstructure with band parameters explains intrinsic physical, chemical and mechanical properties of the solid. Here we report the artificial polaritonic bandstructures of two-dimensional honeycomb lattices for microcavity exciton-polaritons using GaAs semiconductors in the wide-range detuning values, from cavity-photon-like (red-detuned) to exciton-like (blue-detuned) regimes. In order to understand the experimental bandstructures and their band parameters, such as gap energies, bandwidths, hopping integrals and density of states, we originally establish a polariton band theory within an augmented plane wave method with two-kind-bosons, cavity photons trapped at the lattice sites and freely moving excitons. In particular, this two-kind-band theory is absolutely essential to elucidate the exciton effect in the bandstructures of blue-detuned exciton-polaritons, where the flattened exciton-like dispersion appears at larger in-plane momentum values captured in our experimental access window. We reach an excellent agreement between theory and experiments in all detuning values.

cond-mat.mes-hall↗

arXiv2021

Motional narrowing, ballistic transport, and trapping of room-temperature exciton polaritons in an atomically-thin semiconductor

Atomically-thin transition metal dichalcogenide crystals (TMDCs) hold great promise for future semiconductor optoelectronics due to their unique electronic and optical properties. In particular, electron-hole pairs (excitons) in TMDCs are stable at room temperature and interact strongly with light. When TMDCs are embedded in an optical microcavity, the excitons can hybridise with cavity photons to form exciton polaritons (polaritons herein), which display both ultrafast velocities and strong interactions. The ability to manipulate and trap polaritons on a microchip is critical for future applications. Here, we create a potential landscape for room-temperature polaritons in monolayer WS$_2$, and demonstrate their free propagation and trapping. We show that the effect of dielectric disorder, which restricts the diffusion of WS$_2$ excitons and broadens their spectral resonance, is dramatically reduced in the strong exciton-photon coupling regime leading to motional narrowing. This enables the ballistic transport of WS$_2$ polaritons across tens of micrometers with an extended range of partial first-order coherence. Moreover, the dephasing of trapped polaritons is dramatically suppressed compared to both WS$_2$ excitons and free polaritons. Our results demonstrate the possibility of long-range transport and efficient trapping of TMDC polaritons in ambient conditions.

cond-mat.mes-hall↗

arXiv2021

Iterated integrals over letters induced by quadratic forms

An automated treatment of iterated integrals based on letters induced by real-valued quadratic forms and Kummer--Poincaré letters is presented. These quantities emerge in analytic single and multi--scale Feynman diagram calculations. To compactify representations, one wishes to apply general properties of these quantities in computer-algebraic implementations. We provide the reduction to basis representations, expansions, analytic continuation and numerical evaluation of these quantities.

hep-th↗

arXiv2021

Polariton Lasing in Micropillars With One Micrometer Diameter and Position-Dependent Spectroscopy of Polaritonic Molecules

Microcavity polaritons are bosonic light-matter particles that can emit coherent radiation without electronic population inversion via bosonic scattering. This phenomenon, known as polariton lasing, strongly depends on the polaritons' confinement. Shrinking the polaritons' mode volume increases the interactions mediated by their excitonic part, and thereby the density-dependent blueshift of the polariton to a higher energy is enhanced. Previously, polariton lasing has been demonstrated in micropillars with diameters larger than three microns, in grating based cavities, fiber cavities and photonic crystal cavities. Here we show polariton lasing in a micropillar with one micron diameter operating in a single transverse mode that can be optimally coupled to a singlemode fiber. We geometrically decouple the excitation with an angle from the collection. From the number of collected photons we calculate the number of polaritons and observe a blueshift large enough to qualify our device for novel schemes of quantum light generation such as the unconventional photon blockade. To that end, we also apply angled excitation to polaritonic molecules and show site-selective excitation and collection of modes with various symmetries.

physics.optics↗

arXiv2021

Purcell-enhanced single photon source based on a deterministically placed WSe$_{2}$ monolayer quantum dot in a circular Bragg grating cavity

We demonstrate a deterministic Purcell-enhanced single-photon source realized by integrating an atomically thin WSe$_{2}$ layer with a circular Bragg grating cavity. The cavity significantly enhances the photoluminescence from the atomically thin layer, and supports single-photon generation with $g^{(2)}(0)<0.25$. We observe a consistent increase of the spontaneous emission rate for WSe$_{2}$ emitters located in the center of the Bragg grating cavity. These WSe$_{2}$ emitters are self-aligned and deterministically coupled to such a broadband cavity, configuring a new generation of deterministic single-photon sources, characterized by their simple and low-cost production and intrinsic scalability.

quant-ph↗

arXiv2021

The Polarized Transition Matrix Element $A_{gq}(N)$ of the Variable Flavor Number Scheme at $O(α_s^3)$

We calculate the polarized massive operator matrix element $A_{gq}^{(3)}(N)$ to 3-loop order in Quantum Chromodynamics analytically at general values of the Mellin variable $N$ both in the single- and double-mass case in the Larin scheme. It is a transition function required in the variable flavor number scheme at $O(α_s^3)$. We also present the results in momentum fraction space.

hep-ph↗

arXiv2020

Observation of intensity squeezing in resonance fluorescence from a solid-state device

Intensity squeezing, i.e., photon number fluctuations below the shot noise limit, is a fundamental aspect of quantum optics and has wide applications in quantum metrology. It was predicted in 1979 that the intensity squeezing could be observed in resonance fluorescence from a two-level quantum system. Yet, its experimental observation in solid states was hindered by inefficiencies in generating, collecting and detecting resonance fluorescence. Here, we report the intensity squeezing in a single-mode fibre-coupled resonance fluorescence single-photon source based on a quantum dot-micropillar system. We detect pulsed single-photon streams with 22.6% system efficiency, which show subshot-noise intensity fluctuation with an intensity squeezing of 0.59 dB. We estimate a corrected squeezing of 3.29 dB at the first lens. The observed intensity squeezing provides the last piece of the fundamental picture of resonance fluorescence; which can be used as a new standard for optical radiation and in scalable quantum metrology with indistinguishable single photons.

quant-ph↗

arXiv2020

Demonstration of a polariton step potential by local variation of light-matter coupling in a van-der-Waals heterostructure

The large oscillator strength of excitons in transition metal dichalcogenide layers facilitates the formation of exciton-polariton resonances for monolayers and van-der-Waals heterostructures embedded in optical microcavities. Here, we show, that locally changing the number of layers in a WSe2/hBN/WSe2 van-der-Waals heterostructure embedded in a monolithic, high-quality-factor cavity gives rise to a local variation of the coupling strength. This effect yields a polaritonic stair case potential, which we demonstrate at room temperature. Our result paves the way towards engineering local polaritonic potentials at length scales down to atomically sharp interfaces, based on purely modifying its real part contribution via the coherent light-matter coupling strength g.

cond-mat.mes-hall↗

arXiv2020

Propagative oscillations in co-directional polariton waveguide couplers

We report on novel exciton-polariton routing devices created to study and purposely guide light-matter particles in their condensate phase. In a co-directional coupling device, two waveguides are connected by a partially etched section which facilitates tunable coupling of the adjacent channels. This evanescent coupling of the two macroscopic wavefunctions in each waveguide reveals itself in real space oscillations of the condensate. This Josephson-like oscillation has only been observed in coupled polariton traps so far. Here, we report on a similar coupling behavior in a controllable, propagative waveguide-based design. By controlling the gap width, channel length or the propagation energy, the exit port of the polariton flow can be chosen. This co-directional polariton device is a passive and scalable coupler element that can serve in compact, next generation logic architectures.

cond-mat.mes-hall↗

arXiv2020

Accurate photon echo timing by optical freezing of exciton dephasing and rephasing in quantum dots

Semiconductor quantum dots are excellent candidates for ultrafast coherent manipulation of qubits by laser pulses on picosecond timescales or even faster. In inhomogeneous ensembles a macroscopic optical polarization decays rapidly due to dephasing, which, however, is reversible in photon echoes carrying complete information about the coherent ensemble dynamics. Control of the echo emission time is mandatory for applications. Here, we propose a novel concept to reach this goal. In a two-pulse photon echo sequence, we apply an additional resonant control pulse with multiple of 2pi area. Depending on its arrival time, the control slows down dephasing or rephasing of the exciton ensemble during its action. We demonstrate for self-assembled (In,Ga)As quantum dots that the photon echo emission time can be retarded or advanced by 5 ps relative to its nominal appearance time without control. This versatile protocol may be used to obtain significantly longer temporal shifts for suitably tailored control pulses.

cond-mat.mes-hall↗

arXiv2020

Impact of the energetic landscape on polariton condensates propagation along a coupler

Polariton condensates propagation is strongly dependent on the particular energy landscape the particles are moving upon, in which the geometry of the pathway laid for their movement plays a crucial role. Bends in the circuits trajectories affect the condensates speed and oblique geometries introduce an additional discretization of the polaritons momenta due to the mixing of short and long axis wavevectors on the propagating eigenvalues. In this work, we study the nature of the propagation of condensates along the arms of a polariton coupler, by a combination of time-resolved micro-tomography measurements and a theoretical model based on a mean field approximation where condensed polaritons are described by an equation for the slow varying amplitude of the polariton field coupled to an equation for the density of incoherent excitons.

cond-mat.mes-hall↗

arXiv2020

The Two-mass Contribution to the Three-Loop Polarized Operator Matrix Element $A_{gg,Q}^{(3)}$

We compute the two-mass contributions to the polarized massive operator matrix element $A_{gg,Q}^{(3)}$ at third order in the strong coupling constant $α_s$ in Quantum Chromodynamics analytically. These corrections are important ingredients for the matching relations in the variable flavor number scheme and for the calculation of Wilson coefficients in deep--inelastic scattering in the asymptotic regime $Q^2 \gg m_c^2, m_b^2$. The analytic result is expressed in terms of nested harmonic, generalized harmonic, cyclotomic and binomial sums in $N$-space and by iterated integrals involving square-root valued arguments in $z$ space, as functions of the mass ratio. Numerical results are presented. New two--scale iterative integrals are calculated.

hep-ph↗

arXiv2019

The three-loop single mass polarized pure singlet operator matrix element

We calculate the massive polarized three-loop pure singlet operator matrix element $A_{Qq}^{(3), \rm PS}$ in the single mass case in the Larin scheme. This operator matrix element contributes to the massive polarized three-loop Wilson coefficient $H_{Qq}^{(3),\rm PS}$ in deep-inelastic scattering and constitutes a three-loop transition matrix element in the variable flavor number scheme. We provide analytic results in Mellin $N$ and in $x$ space and study the behaviour of this operator matrix element in the region of small and large values of the Bjorken variable $x$.

hep-ph↗

arXiv2019

The three-loop polarized pure singlet operator matrix element with two different masses

We present the two-mass QCD contributions to the polarized pure singlet operator matrix element at three loop order in $x$-space. These terms are relevant for calculating the polarized structure function $g_1(x,Q^2)$ at $O(α_s^3)$ as well as for the matching relations in the variable flavor number scheme and the polarized heavy quark distribution functions at the same order. The result for the operator matrix element is given in terms of generalized iterated integrals. These integrals depend on the mass ratio through the main argument, and the alphabet includes square--root valued letters.

hep-ph↗