Cavity optomagnonics with magnetic textures: coupling a magnetic vortex to light

Optomagnonic systems, where light couples coherently to collective excitations in magnetically ordered solids, are currently of high interest due to their potential for quantum information processing platforms at the nanoscale. Efforts so far, both at the experimental and theoretical level, have focused on systems with a homogeneous magnetic background. A unique feature in optomagnonics is however the possibility of coupling light to spin excitations on top of magnetic textures. We propose a cavity-optomagnonic system with a non homogeneous magnetic ground state, namely a vortex in a magnetic microdisk. In particular we study the coupling between optical whispering gallery modes to magnon modes localized at the vortex. We show that the optomagnonic coupling has a rich spatial structure and that it can be tuned by an externally applied magnetic field. Our results predict cooperativities at maximum photon density of the order of $\mathcal{C}\approx10^{-2}$ by proper engineering of these structures.Comment: 16 pages, 11 figures, published versio

Method-based caching in multi-tiered server applications

Abstract In recent years, application server technology has become very popular for building complex but mission-critical systems such as Web-based E-Commerce applications. However, the resulting solutions tend to suffer from serious performance and scalability bottlenecks, because of their distributed nature and their various software layers. This paper deals with the problem by presenting an approach about transparently caching results of a service interface\u27s read-only methods on the client side. Cache consistency is provided by a descriptive cache invalidation model which may be specified by an application programmer. As the cache layer is transparent to the server as well as to the client code, it can be integrated with relatively low effort even in systems that have already been implemented. Experimental results show that the approach is very effective in improving a server\u27s response times and its transactional throughput. Roughly speaking, the overhead for cache maintenance is small when compared to the cost for method invocations on the server side. The cache\u27s performance improvements are dominated by the fraction of read method invocations and the cache hit rate. Our experiments are based on a realistic E-commerce Web site scenario and site user behaviour is emulated in an authentic way. By inserting our cache, the maximum user request throughput of the web application could be more than doubled while its response time (such as perceived by a web client) was kept at a very low level. Moreover, the cache can be smoothly integrated with traditional caching strategies acting on other system tiers (e.g. caching of dynamic Web pages on a Web server). The presented approach as well as the related implementation are not restricted to application server scenarios but may be applied to any kind of interface-based software layers

Generation and subwavelength focusing of longitudinal magnetic fields in a metallized fiber tip

We demonstrate experimentally and numerically that in fiber tips as they are used in NSOMs azimuthally polarized electrical fields (|E$_{\text{azi}}$|$^2$/|E$_{\text{tot}}$|$^2$ $\approx$ 55% $\pm$ 5% for 1.4\mu m tip aperture diameter and \lambda$_0$ = 1550nm), respectively subwavelength confined (FWHM $\approx$ 450nm $\approx$ \lambda$_0$/3.5) magnetic fields, are generated for a certain tip aperture diameter (d = 1.4\mu m). We attribute the generation of this field distribution in metal-coated fiber tips to symmetry breaking in the bend and subsequent plasmonic mode filtering in the truncated conical taper.Comment: 11 pages, 6 figure

Position-squared coupling in a tunable photonic crystal optomechanical cavity

We present the design, fabrication, and characterization of a planar silicon photonic crystal cavity in which large position-squared optomechanical coupling is realized. The device consists of a double-slotted photonic crystal structure in which motion of a central beam mode couples to two high-Q optical modes localized around each slot. Electrostatic tuning of the structure is used to controllably hybridize the optical modes into supermodes which couple in a quadratic fashion to the motion of the beam. From independent measurements of the anti-crossing of the optical modes and of the optical spring effect, the position-squared vacuum coupling rate is measured to be as large as 245 Hz to the fundamental in-plane mechanical resonance of the structure at 8.7MHz, which in displacement units corresponds to a coupling coefficient of 1 THz/nm$^2$. This level of position-squared coupling is approximately five orders of magnitude larger than in conventional Fabry-Perot cavity systems.Comment: 11 pages, 6 figure

Design of tunable GHz-frequency optomechanical crystal resonators

We present a silicon optomechanical nanobeam design with a dynamically tunable acoustic mode at 10.2 GHz. The resonance frequency can be shifted by 90 kHz/V^2 with an on-chip capacitor that was optimized to exert forces up to 1 µN at 10 V operation voltage. Optical resonance frequencies around 190 THz with Q-factors up to 2.2 × 10^6 place the structure in the well-resolved sideband regime with vacuum optomechanical coupling rates up to g_0/2π = 353 kHz. Tuning can be used, for instance, to overcome variation in the device-to-device acoustic resonance frequency due to fabrication errors, paving the way for optomechanical circuits consisting of arrays of optomechanical cavities

Direct laser-written optomechanical membranes in fiber Fabry-Perot cavities

Integrated micro and nanophotonic optomechanical experiments enable the manipulation of mechanical resonators on the single phonon level. Interfacing these structures requires elaborate techniques limited in tunability, flexibility, and scaling towards multi-mode systems. Here, we demonstrate a cavity optomechanical experiment using 3D-laser-written polymer membranes inside fiber Fabry-Perot cavities. Vacuum coupling strengths of ~ 30 kHz to the fundamental megahertz mechanical mode are reached. We observe optomechanical spring tuning of the mechanical resonator by tens of kHz exceeding its linewidth at cryogenic temperatures. The extreme flexibility of the laser writing process allows for a direct integration of the membrane into the microscopic cavity. The direct fiber coupling, its scaling capabilities to coupled resonator systems, and the potential implementation of dissipation dilution structures and integration of electrodes make it a promising platform for fiber-tip integrated accelerometers, optomechanically tunable multi-mode mechanical systems, or directly fiber-coupled systems for microwave to optics conversion.Comment: 10 pages, 5 figure

Functionalization of Graphite Electrodes with Aryl Diazonium Salts for Lithium‐Ion Batteries

The functionalization of electrode surfaces is a useful approach to gain a better understanding of solid–electrolyte interphase formation and battery performance in lithium-ion batteries (LIBs). Electrografting and deprotection of alkyl silyl protected ethynyl aryl diazonium salts on graphite electrodes were performed. Furthermore, electrografting of aryl diazonium salts carrying functional groups such as amino, carboxy and nitro, and their influence on the electrochemical performance in LIBs were investigated. The drawbacks of electrografted and especially deprotected samples were evaluated and compared to corresponding in situ grafted samples. While electrografted samples tend to lower the delithiation capacities, in situ grafted samples, except amino groups, reveal higher capacities. Ethynyl (TMS) shows improved capacities at 1 C and better capacity retention compared to the pristine graphite electrode. Additionally, the Coulombic efficiency of the first cycle was enhanced for in situ grafted samples