arXiv subjects

Falk Eilenberger

Publications and source records attributed to Falk Eilenberger.

At least 55 records · Page 3Linked to original sources

arXiv2023

Approaching optimal entangling collective measurements on quantum computing platforms

Entanglement is a fundamental feature of quantum mechanics and holds great promise for enhancing metrology and communications. Much of the focus of quantum metrology so far has been on generating highly entangled quantum states that offer better sensitivity, per resource, than what can be achieved classically. However, to reach the ultimate limits in multi-parameter quantum metrology and quantum information processing tasks, collective measurements, which generate entanglement between multiple copies of the quantum state, are necessary. Here, we experimentally demonstrate theoretically optimal single- and two-copy collective measurements for simultaneously estimating two non-commuting qubit rotations. This allows us to implement quantum-enhanced sensing, for which the metrological gain persists for high levels of decoherence, and to draw fundamental insights about the interpretation of the uncertainty principle. We implement our optimal measurements on superconducting, trapped-ion and photonic systems, providing an indication of how future quantum-enhanced sensing networks may look.

quant-ph↗

arXiv2023

Localized creation of yellow single photon emitting carbon complexes in hexagonal boron nitride

Single photon emitters in solid-state crystals have received a lot of attention as building blocks for numerous quantum technology applications. Fluorescent defects in hexagonal boron nitride (hBN) stand out due to their high luminosity and robust operation at room temperature. The identical emitter fabrication at pre-defined sites is still challenging, which hampers the integration of these defects in optical systems and electro-optical devices. Here, we demonstrate the localized fabrication of hBN emitter arrays by electron beam irradiation using a standard scanning electron microscope with deep sub-micron lateral precision. The emitters are created with a high yield and a reproducible spectrum peaking at 575 nm. Our measurements of optically detected magnetic resonance have not revealed any addressable spin states. Using density functional theory, we attribute the experimentally observed emission lines to carbon-related defects, which are activated by the electron beam. Our scalable approach provides a promising pathway for fabricating room temperature single photon emitters in integrated quantum devices.

quant-ph↗

arXiv2023

Ultra-bright single photon source based on an atomically thin material

Solid-state single photon sources are central building blocks in quantum communication networks and on-chip quantum information processing. Atomically thin crystals were established as possible candidates to emit non-classical states of light, however, the performance of monolayer-based single photon sources has so far been lacking behind state-of-the-art devices based on volume crystals. Here, we implement a single photon source based on an atomically thin sheet of WSe2 coupled to a spectrally tunable optical cavity. It is characterized by a high single photon purity with a $g^{(2)}(0)$ value as low as $4.7 \pm 0.7 \%$ and a record-high first lens brightness of linearly polarized photons as large as $65 \pm 4 \%$. Interestingly, the high performance of our devices allows us to observe genuine quantum interference phenomena in a Hong-Ou-Mandel experiment. Our results demonstrate that open cavities and two-dimensional materials constitute an excellent platform for ultra-bright quantum light sources: the unique properties of such two-dimensional materials and the versatility of open cavities open an inspiring avenue for novel quantum optoelectronic devices.

quant-ph↗

arXiv2023

Enhanced Surface Second Harmonic Generation in Nanolaminates

Second-harmonic generation (SHG) is a second-order nonlinear optical process that is not allowed in media with inversion sym-metry. However, due to the broken symmetry at the surface, surface SHG still occurs, but is generally small. We experimentally investi-gate the surface SHG in periodic stacks of alternating, subwave-length dielectric layers, which have a large number of surfaces, thus enhancing surface SHG considerably. To this end, multilayer stacks of SiO2/TiO2 were grown by Plasma Enhanced Atomic Layer Deposition (PEALD) on fused silica substrates. With this technique individual layers of a thickness of less than 2 nm can be fabricated. We experimentally show that under large angles of incidence (> 20 degrees) there is substantial SHG, well beyond the level, which can be observed from simple interfaces. We perform this experiment for samples with different periods and thickness of SiO2/TiO2 and our results are in agreement with theoretical calculations.

physics.optics↗

arXiv2022

Direct Growth of Monolayer MoS$_2$ on Nanostructured Silicon Waveguides

We report for the first time the direct growth of Molybdenum disulfide (MoS$_2$) monolayers on nanostructured silicon-on-insulator waveguides. Our results indicate the possibility of utilizing the Chemical Vapour Deposition (CVD) on nanostructured photonic devices in a scalable process. Direct growth of 2D material on nanostructures rectifies many drawbacks of the transfer-based approaches. We show that the van der Waals materials grow conformally across the curves, edges, and the silicon-SiO$_2$ interface of the waveguide structure. Here, the waveguide structure used as a growth substrate is complex not just in terms of its geometry but also due to the two materials (Si and SiO$_2$) involved. A transfer-free method like this yields a novel approach for functionalizing nanostructured, integrated optical architectures with an optically active direct semiconductor.

physics.app-ph↗

arXiv2022

Brightening of a dark monolayer semiconductor via strong light-matter coupling in a cavity

Engineering the properties of quantum materials via strong light-matter coupling is a compelling research direction with a multiplicity of modern applications. Those range from modifying charge transport in organic molecules, steering particle correlation and interactions, and even controlling chemical reactions. Here, we study the modification of the material properties via strong coupling and demonstrate an effective inversion of the excitonic band-ordering in a monolayer of WSe2 with spin-forbidden, optically dark ground state. In our experiments, we harness the strong light-matter coupling between cavity photon and the high energy, spin-allowed bright exciton, and thus creating two bright polaritonic modes in the optical bandgap with the lower polariton mode pushed below the WSe2 dark state. We demonstrate that in this regime the commonly observed luminescence quenching stemming from the fast relaxation to the dark ground state is prevented, which results in the brightening of this intrinsically dark material. We probe this effective brightening by temperature-dependent photoluminescence, and we find an excellent agreement with a theoretical model accounting for the inversion of the band ordering and phonon-assisted polariton relaxation.

cond-mat.mes-hall↗

arXiv2022

Picosecond Hyperspectral Fringe Pattern Projection for 3D Surface Measurement

Active stereovision systems for the 3D measurement of surfaces rely on the sequential projection of different fringe patterns onto the scene to robustly and accurately generate 3D surface data. This limits the temporal resolution to the time by which a sufficiently high number of patterns can be projected and recorded. By encoding patterns spectrally and recording them with a hyperspectral imager, it is possible to record several patterns in a single image, limiting the temporal resolution to only the duration of the illumination. A picosecond 3D surface measurement was demonstrated using a high pulse energy femtosecond Ti:Sa laser, spectrally broadened in a hollow core fiber, and two hyperspectral cameras recording the patterns generated by diffraction at an Echelle grating.

physics.optics↗

arXiv2021

Spatial coherence of room-temperature monolayer WSe$_2$ exciton-polaritons in a trap

The emergence of spatial and temporal coherence of light emitted from solid-state systems is a fundamental phenomenon, rooting in a plethora of microscopic processes. It is intrinsically aligned with the control of light-matter coupling, and canonical for laser oscillation. However, it also emerges in the superradiance of multiple, phase-locked emitters, and more recently, coherence and long-range order have been investigated in bosonic condensates of thermalized light, as well as in exciton-polaritons driven to a ground state via stimulated scattering. Here, we experimentally show that the interaction between photons in a Fabry-Perot microcavity and excitons in an atomically thin WSe$_2$ layer is sufficient such that the system enters the hybridized regime of strong light-matter coupling at ambient conditions. Via Michelson interferometry, we capture clear evidence of increased spatial and temporal coherence of the emitted light from the spatially confined system ground-state. The coherence build-up is accompanied by a threshold-like behaviour of the emitted light intensity, which is a fingerprint of a polariton laser effect. Valley-physics is manifested in the presence of an external magnetic field, which allows us to manipulate K and K' polaritons via the Valley-Zeeman-effect. Our findings are of high application relevance, as they confirm the possibility to use atomically thin crystals as simple and versatile components of coherent light-sources, and in valleytronic applications at room temperature.

cond-mat.mes-hall↗

arXiv2021

In-fiber second-harmonic generation with embedded two-dimensional materials

Silica-based optical fibers are a workhorse of nonlinear optics. They have been used to demonstrate nonlinear phenomena such as solitons and self-phase modulation. Since the introduction of the photonic crystal fiber, they have found many exciting applications, such as supercontinuum white light sources and third-harmonic generation, among others. They stand out by their low loss, large interaction length, and the ability to engineer its dispersive properties, which compensate for the small chi(3) nonlinear coefficient. However, they have one fundamental limitation: due to the amorphous nature of silica, they do not exhibit second-order nonlinearity, except for minor contributions from surfaces. Here, we demonstrate significant second-harmonic generation in functionalized optical fibers with a monolayer of highly nonlinear MoS2 deposited on the fiber guiding core. The demonstration is carried out in a 3.5 mm short piece of exposed core fiber, which was functionalized in a scalable process CVD-based process, without a manual transfer step. This approach is scalable and can be generalized to other transition metal dichalcogenides and other waveguide systems. We achieve an enhancement of more than 1000x over a reference sample of equal length. Our simple proof-of-principle demonstration does not rely on either phase matching to fundamental modes, or ordered growth of monolayer crystals, suggesting that pathways for further improvement are within reach. Our results do not just demonstrate a new path towards efficient in-fiber SHG-sources, instead, they establish a platform with a new route to chi(2)-based nonlinear fiber optics, optoelectronics, and photonics platforms, integrated optical architectures, and active fiber networks.

physics.optics↗

arXiv2021

Sensitive single-photon test of extended quantum theory with 2D hexagonal boron nitride

Quantum theory is the foundation of modern physics. Some of its basic principles, such as Born's rule, however, are based on postulates which require experimental testing. Any deviation from Born's rule would result in higher-order interference and can thus be tested in an experiment. Here, we report on such a test with a quantum light source based on a color center in hexagonal boron nitride (hBN) coupled to a microcavity. Our room temperature photon source features a narrow linewidth, high efficiency, high purity, and on-demand single-photon generation. With the single-photon source we can increase the interferometric sensitivity of our three-path interferometer compared to conventional laser-based light sources by fully suppressing the detector nonlinearity. We thereby obtain a tight bound on the third-order interference term of $3.96(523)\times 10^{-4}$. We also measure an interference visibility of 98.58% for our single-photons emitted from hBN at room temperature, which provides a promising route for using the hBN platform as light source for phase-encoding schemes in quantum key distribution.

quant-ph↗

arXiv2021

Fully tunable exciton-polaritons emerging from WS$_{2}$ monolayer excitons in an optical lattice at room temperature

Engineering non-linear hybrid light-matter states in tailored optical lattices is a central research strategy for the simulation of complex Hamiltonians. Excitons in atomically thin crystals are an ideal active medium for such purposes, since they couple strongly with light and bear the potential to harness giant non-linearities and interactions while presenting a simple sample-processing and room temperature operability. We demonstrate lattice polaritons, based on an open, high-quality optical cavity, with an imprinted photonic lattice strongly coupled to excitons in a WS$_{2}$ monolayer. We experimentally observe the emergence of the canonical band-structure of particles in a one-dimensional lattice at room temperature, and demonstrate frequency reconfigurability over a spectral window exceeding 12 meV, as well as the systematic variation of the nearest neighbour coupling, reflected by a tuneability in the bandwidth of the p-band polaritons by 7 meV. The technology presented in this work is a critical demonstration towards reconfigurable photonic emulators operated with non-linear photonic fluids, offering a simple experimental implementation and working at ambient conditions.

cond-mat.mes-hall↗

arXiv2020

Scalable functionalization of optical fibers using atomically thin semiconductors

Atomically thin transition metal dichalcogenides are highly promising for integrated optoelectronic and photonic systems due to their exciton-driven linear and nonlinear interaction with light. Integrating them into optical fibers yields novel opportunities in optical communication, remote sensing, and all-fiber optoelectronics. However, scalable and reproducible deposition of high quality monolayers on optical fibers is a challenge. Here, we report the chemical vapor deposition of monolayer MoS2 and WS2 crystals on the core of microstructured exposed core optical fibers and their interaction with the fibers' guided modes. We demonstrate two distinct application possibilities of 2D-functionalized waveguides to exemplify their potential. First, we simultaneously excite and collect excitonic 2D material photoluminescence with the fiber modes, opening a novel route to remote sensing. Then we show that third harmonic generation is modified by the highly localized nonlinear polarization of the monolayers, yielding a new avenue to tailor nonlinear optical processes in fibers. We anticipate that our results may lead to significant advances in optical fiber based technologies.

physics.app-ph↗

arXiv2020

Nanostructure-modulated planar high spectral resolution spectro-polarimeter

We present a planar spectro-polarimeter based on Fabry-P{é}rot cavities with embedded polarization-sensitive high-index nanostructures. A $7~μ$m-thick spectro-polarimetric system for 3 spectral bands and 2 linear polarization states is experimentally demonstrated. Furthermore, an optimal design is theoretically proposed, estimating that a system with a bandwidth of 127~nm and a spectral resolution of 1~nm is able to reconstruct the first three Stokes parameters \textcolor{black}{with a signal-to-noise ratio of -13.14~dB with respect to the the shot noise limited SNR}. The pixelated spectro-polarimetric system can be directly integrated on a sensor, thus enabling applicability in a variety of miniaturized optical devices, including but not limited to satellites for Earth observation.

physics.optics↗

arXiv2020

Discrete dispersion scan setup for measuring few-cycle laser pulses in the mid-infrared

In this work, we demonstrate a discrete dispersion scan scheme using a low number of flat windows to vary the dispersion of laser pulses in discrete steps. Monte Carlo simulations indicate that the pulse duration can be retrieved accurately with less than 10 dispersion steps, which we verify experimentally by measuring few-cycle pulses and material dispersion curves at 3 and 10 micrometer wavelength. This minimal measuring scheme using only five optical components without the need for high-precision positioners and interferometric alignment can be readily implemented in many wavelength ranges and situations.

physics.optics↗

arXiv2019

Magnetic field induced splitting and polarization of monolayer-based valley exciton-polaritons

Atomically thin crystals of transition metal dichalcogenides are ideally suited to study the interplay of light-matter coupling, polarization and magnetic field effects. In this work, we investiagte the formation of exciton-polaritons in a MoSe2 monolayer, which is integrated in a fully-grown, monolithic microcavity. Due to the narrow linewidth of the polaritonic resonances, we are able to directly investigate the emerging valley Zeeman splitting of the hybrid light-matter resonances in the presence of a magnetic field. At a detuning of -54.5 meV (13.5 % matter constituent of the lower polariton branch), we find a Zeeman splitting of the lower polariton branch of 0.36 meV, which can be directly associated with an excitonic g factor of 3.94\pm0.13. Remarkably, we find that a magnetic field of 6T is sufficient to induce a notable valley polarization of 15 % in our polariton system, which approaches 30% at 9T. Strikingly, this circular polarization degree of the polariton (ground) state exceeds the polarization of the exciton reservoir for equal magnetic field magnitudes by approximately 50%, as a consequence of enhanced relaxation of bosons in our monolayer-based system.

cond-mat.mes-hall↗

arXiv2018

Integration of atomically thin layers of transition metal dichalcogenides into high-Q, monolithic Bragg-cavities - an experimental platform for the enhancement of optical interaction in 2D-materials

We demonstrate a new approach to integrate single layer MoSeR2R and WSeR2R flakes into monolithic all-dielectric planar high-quality micro-cavities. These distributed-Bragg-reflector (DBR) cavities may e.g. be tuned to match the exciton resonance of the 2D-materials. They are highly robust and compatible with cryogenic and room-temperature operation. The integration is achieved by a customized ion-assisted physical vapor deposition technique, which does not degrade the optical properties of the 2D-materials. The monolithic 2D resonator is shown to have a high Q-factor in excess of 4500. We use photoluminescence (PL) experiments to demonstrate that the coating procedure with an SiO2 coating on a prepared surface does not significantly alter the electrooptical properties of the 2D-materials. Moreover, we observe a resonance induced modification of the PL-spectrum for the DBR embedded flake. Our system thus represents a versatile platform to resonantly enhance and tailor light-matter-interaction in 2D-materials. The gentle processing conditions would also allow the integration of other sensitive materials into these highly resonant structures.

physics.optics↗

arXiv2018

Common pulse retrieval algorithm: a fast and universal method to retrieve ultrashort pulses

We present a common pulse retrieval algorithm (COPRA) that can be used for a broad category of ultrashort laser pulse measurement schemes including frequency-resolved optical gating (FROG), interferometric FROG, dispersion scan, time domain ptychography, and pulse shaper assisted techniques such as multiphoton intrapulse interference phase scan (MIIPS). We demonstrate its properties in comprehensive numerical tests and show that it is fast, reliable and accurate in the presence of Gaussian noise. For FROG it outperforms retrieval algorithms based on generalized projections and ptychography. Furthermore, we discuss the pulse retrieval problem as a nonlinear least-squares problem and demonstrate the importance of obtaining a least-squares solution for noisy data. These results improve and extend the possibilities of numerical pulse retrieval. COPRA is faster and provides more accurate results in comparison to existing retrieval algorithms. Furthermore, it enables full pulse retrieval from measurements for which no retrieval algorithm was known before, e.g., MIIPS measurements.

physics.ins-det↗

arXiv2018

Dynamics of liquid crystal on hexagonal lattice

Nematic liquid crystal (LC) molecules adsorbed on two dimensional materials are aligned along the crystal directions of the hexagonal lattice. It was demonstrated that short electric pulses can reorient the aligned LC molecules in the preferred armchair direction of hexagonal boron nitride (h-BN). Several states with a variety of colors were obtained by changing the direction and strength of the electric pulses. The ab initio calculations based on density functional theory was carried out to determine the favorable adsorption configurations of the LC molecules on the h-BN surface. A non-volatile display, in which pixel resolution can be determined by grains of hexagonal surface, is proposed, which can offer a pathway towards dynamic high-quality pixels with low power consumption, and could define a new paradigm for all non-volatile display applications.

cond-mat.soft↗