A theoretical model with experimental verification is presented to enhance the quantum efficiency of a superconducting single-photon detector without increasing the length or thickness of the active element. The basic enhancement framework is based on: (1) Utilizing the plasmonic nature of a superconducting layer to increase the surface absorption of the input optical signal. (2) Enhancing the critical current of the nanowires by reducing the current crowding at the bend areas through optimally rounded-bend implementation. The experimental system quantum efficiency and fluctuation rates per second are assessed and compared to the proposed theoretical model. The model originated from an accurate description of the different liberation mechanisms of the nano-patterned superconducting films (vortex hopping and vortex-antivortex pairing). It is built complimentary to the existing, well-established models by considering the effects of quantum confinement on the singularities' energy states. The proposed model explains the dynamics of singularities for a wide range of temperatures and widths and describe an accurate count rate behavior for the structure. Furthermore, it explains the abnormal behaviors of the measured fluctuation rates occurring in wide nano-patterned superconducting structures below the critical temperature. In accordance to this model, it has been shown that for a typical strip width, not only is the vortex-antivortex liberation higher than the predicted rate, but also quantum tunneling is significant in certain conditions, and cannot be neglected as it has been in previous models. Also it is concluded that to satisfy both optical guiding and photon detection considerations of the design, the width and the thickness of the superconducting wires should be carefully determined in order to maintain the device sensitivity while crossing over from the current crowding to vortex-based detection mechanisms.

Die vorliegende Doktorarbeit beschäftigt sich mit der experimentellen Studie zweier miteinander verbundener Phänomene: Dem intrinsischen Timing-Jitter in einem supraleitendenden Nanodraht-Einzelphotonen-Detektor (SNSPD) und der Relaxation der Elektronenenergie in supraleitenden Filmen. Supraleitende Nanodrähte auf einem dielektrischen Substrat als mikroskopische Grundbausteine jeglicher SNSPDs stellen sowohl für theoretische als auch für experimentelle Studien komplexe Objekte dar. Die Komplexität ergibt sich aus der Tatsache, dass SNSPDs in der Praxis stark ungeordnete und ultradünne supraleitende Filme verwenden, die eine akustische Fehlanpassung zu dem zugrundeliegenden Substrat aufweisen und einen Nichtgleichgewichts-Zustand implizieren. Die Arbeit untersucht die Komplexität des am weitesten in der SNSPD Technologie verbreiteten Materials, Niobnitrid (NbN), indem verschiedene experimentelle Methoden angewandt werden. Als eine mögliche Anwendung der SNSPD-Technologie wird ein Prototyp eines dispersiven Raman-Spektrometers mit Einzelphotonen-Sensitivität demonstriert. / This Ph.D. thesis is based on the experimental study of two mutually interconnected phenomena: intrinsic timing jitter in superconducting nanowire single-photon detectors (SNSPDs) and relaxation of the electron energy in superconducting films. Microscopically, a building element of any SNSPD device, a superconducting nanowire on top of a dielectric substrate, represents a complex object for both experimental and theoretical studies. The complexity arises because, in practice, the SNSPD utilizes strongly disordered and ultrathin superconducting films, which acoustically mismatch with the underlying substrate, and implies a non-equilibrium state. This thesis addresses the complexity of the most conventional superconducting material used in SNSPD technology, niobium nitride (NbN), by applying several distinct experimental techniques. As an emerging application of the SNSPD technology, we demonstrate a prototype of the dispersive Raman spectrometer with single-photon sensitivity.