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Aufsatz
Extreme Ultraviolet to Visible Dispersed Single Photon Detection for Highly Sensitive Sensing of Fundamental Processes in Diverse Samples
(2018-05-23)
The detection of a single photon is the most sensitive method for sensing of photon emission. A common technique for single photon detection uses microchannel plate arrays combined with photocathodes and position sensitive anodes. Here, we report on the combination of such detectors with grating diffraction spectrometers, constituting a low-noise wavelength resolving photon spectroscopy apparatus with versatile applicability. We recapitulate the operation principle of such detectors and present the details of the ...
Dissertation
A new perspective to strongly-interacting lattice fermions in the framework of density functional theory
(2020)
Die in dieser Arbeit formulierte Theorie betrachtet das Vielteilchenproblem wechselwirkender Fermionen auf einem Gitter aus einem neuen Blickwinkel.
Dissertation
High temperature-stable InGaAs QDs for the monolithic integration in external-cavity surface-emitting lasers
(2021)
Optically pumped vertical external-cavity surface-emitting lasers (VECSELs), also called semiconductor disk lasers (SDLs), benefit from the flexibility and versatility of the semiconductor material. With a simple cavity layout, fundamental transverse mode operation with a circular output beam and high beam quality is possible. They have excellent heat-sink properties and only require inexpensive multimode diode lasers for pumping. The complete VECSEL structure is only a few micrometers thick which leads to a strong ...
Aufsatz
Beating the limits with initial correlations
(2017-11-28)
Fast and reliable reset of a qubit is a key prerequisite for any quantum technology. For real world open quantum systems undergoing non-Markovian dynamics, reset implies not only purification, but in particular erasure of initial correlations between qubit and environment. Here, we derive optimal reset protocols using a combination of geometric and numerical control theory. For factorizing initial states, we find a lower limit for the entropy reduction of the qubit as well as a speed limit. The time-optimal solution ...
Dissertation
High-Speed 1.55 µm Quantum Dot Lasers with Electronically Coupled Quantum Well - Dot Active Regions
(2019-07-31)
The expansion of long-distance data communication at a wavelength of 1.55 µm calls for larger data transfer rates. Consequently, an improvement of emission and modulation properties of lasers emitting in this wavelength region is of high interest. The utilization of so-called tunnel-injection (TI) structures in InP-based quantum dot (QD) lasers is promising to fulfill this task. The aim of this thesis was the realization and analysis of TI structures in the lattice matched InP material system and incorporation into ...
Dissertation
Fabrication and characterization of diamond nanopillars, waveguides and AFM tips with incorporated color centers
(2020-06)
Diamond is a unique material with outstanding properties and the perfect host for different crystal defects in its lattice, so-called color centers, which provide exceptional spin properties, rendering them a promising platform for the development of novel devices and components in quantum information technologies (QIT) and quantum sensing applications. To overcome diamond's high internal reflection due to its high refractive index, color centers need to be incorporated in photonic diamond structures, leading to ...
Dissertation
Analysis of near-substrate magnetic particle transport for Lab-on-a-chip applications: stray field modulations, influence of particle properties and three-dimensional trajectories
(2022)
Die Entwicklung schneller und zuverlässiger Diagnostik ist ein wichtiges Ziel für die Früherkennung von Krankheiten. Standardisierte Labormethoden sind heutzutage meist langsam und mit hohen Kosten verbunden. Innerhalb der Lab-on-a-chip (LOC)-Technologie kann der Nachweis eines pathogenen Organismus auf die Größe eines kleinen Chips miniaturisiert werden, indem magnetische Partikel als Fängerobjekte integriert werden. Die Kombination einer statischen Magnetfeldlandschaft (MFL) mit zeitlich variierenden externen ...
Dissertation
Magnetic Textures and Magnetization Reversal Processes in Arrays of Ferromagnetic and Exchange-Biased Hollow Hemispheres
(2022)
The main objective of this thesis is to investigate hemispherical caps prepared by thin film deposition of magnetic material compositions on top of nano- and micrometer sized silica spheres. When compared to flat magnetic discs, these microcaps differ in their magnetic properties due to the curved and therefore three-dimensional shape. However, under certain conditions, both microstructures have previously been proven to express the famous magnetic vortex texture because of the confinement into a circular shape. ...
Dissertation
Electronic Theory of the Magnetic Order, Anisotropy and Reversal Processes in Rolled-Up Stripes and Thin Films
(2022)
A comprehensive multiscale approach consisting of a combination of state of the art, first principles quantum theory and the flexible statistical methodologies of complex systems is applied in order to achieve a detailed microscopic understanding of the magnetic properties of rolled-up transition-metal [TM] ultrathin films and stripes. A quantum electronic investigations of the effective interactions between the local magnetic moments is performed as a function of composition and rolling radius R including the limit ...
Dissertation
Investigations on Diamond Thin Films as Implant Coating and Biosensing Platform
(2021)
Diamond is researched in biological context for decades. Fundamental research has established diamond as a material that combines a pronounced compatibility with biological entities and resilience against even the harshest chemical and physical conditions. The present dissertation strives to improve the abilities of diamond in this matter even further by utilizing methods of nanostructuring and biochemical functionalization. Numerous characterization methods are used to monitor each step in detail and to evaluate the ...