Integrated quantum optical networks based on quantum dots and photonic crystals

Single solid-state optical emitters have quantum mechanical properties that make them suitable for applications in information processing and sensing. Most of these quantum technologies rely on the capability to integrate the emitters in reliable solid-state optical networks. In this paper, we present integrated devices based on GaAs photonic crystals and InAs self-assembled quantum dots. These quantum networks are well suited to future optoelectronic devices operating at ultralow power levels, single-photon logic devices and quantum information processing

Exploring High Resolution Test Pattern To Improve The Cache Failure Analysis

Typically, only pass/fail basis test algorithm is being used to test the cache array in silicon devices. But the pass/fail basis test algorithm is insufficient to identify the failing characteristic of the cache array when it comes to the failure analysis (FA) and debug stage to find out the root cause of the failing mechanism. The resolution of test algorithm plays an important role in helping FA process to identify every single failing bits in cache array. In this dissertation, the concept of bringing up the Memory Build in Self-Test (MBIST) high resolution test pattern is discussed. The utilization of MBIST engine by insertion of the Capture Test Vector (CTV) element into the test algorithm is the main concept in increasing the resolution test pattern. At the same time, the importance of high resolution test pattern in FA process is being shown in a real case study. The generated high resolution test pattern is integrated for Automated Test Equipment (ATE) usage so that the test pattern can be applied in real silicon device testing. Then, a silicon device is edited using Focused Ion Beam (FIB) to destroy the memory bits in cache array for proving the test pattern is functioning properly. Finally, the high resolution test pattern is being used in real case application for proving the high resolution test pattern have the capability in improving FA efficiency in identifying the failing bits. The FA technique and application of using high resolution test pattern in debugging the cache failure are shown from the testing stage until the destructive FA stage. The finding in real case FA proved the concept of bring up the MBIST high resolution test pattern is working properly. It is able to increase the effectiveness of failure analysis and failure isolation process which indirectly increase the success rate for finding the root cause

Hot Electrons Regain Coherence in Semiconducting Nanowires

The higher the energy of a particle is above equilibrium the faster it relaxes due to the growing phase-space of available electronic states it can interact with. In the relaxation process phase coherence is lost, thus limiting high energy quantum control and manipulation. In one-dimensional systems high relaxation rates are expected to destabilize electronic quasiparticles. We show here that the decoherence induced by relaxation of hot electrons in one-dimensional semiconducting nanowires evolves non-monotonically with energy such that above a certain threshold hot-electrons regain stability with increasing energy. We directly observe this phenomenon by visualizing for the first time the interference patterns of the quasi-one-dimensional electrons using scanning tunneling microscopy. We visualize both the phase coherence length of the one-dimensional electrons, as well as their phase coherence time, captured by crystallographic Fabry-Perot resonators. A remarkable agreement with a theoretical model reveals that the non-monotonic behavior is driven by the unique manner in which one dimensional hot-electrons interact with the cold electrons occupying the Fermi-sea. This newly discovered relaxation profile suggests a high-energy regime for operating quantum applications that necessitate extended coherence or long thermalization times, and may stabilize electronic quasiparticles in one dimension

Emergent Phenomena in Spatially Confined Manganites

Rare earth manganites exhibit colossal magnetoresistance (CMR). There is evidence that alloyed single crystal materials in this class can display electronic inhomogeneity in which areas with vastly different electronic and magnetic properties can form and coexist in phase separated domains ranging in size from a few nanometers to micrometers. This phase separation (PS) is of particular interest, as it has been suggested that it is the central feature that leads to CMR in manganites, the Mott transition in VO2 and may play a role in high-TC superconductivity in cuprates. However there is debate as to its precise role. The purpose of my research is to answer fundamental questions about the specific role of PS in complex oxides. I reduce single crystal thin films of an electronically phase separated manganite to the scale of their inherent electronic phase domains near the metal-insulator transition. Unlike transport measurements done on bulk or thin films where the electrons follow only the metallic path of least resistance, this configuration forces electrons to travel through both the metallic and insulating regions residing in the material. This has led to observations of several new phenomena such as a reemergent metal-insulator transition, ultra-sharp jumps in resistivity at the metal-insulator transition, and the first high resolution observation of single domain electronic phase transitions in the time domain. While the manganites will be the primary focus throughout this dissertation, the spatial confinement techniques presented here are not limited to only these materials. They can be applied to any phase separated system to probe regions resistively hidden to transport measurements

Towards understanding two-level-systems in amorphous solids -- Insights from quantum circuits

Amorphous solids show surprisingly universal behaviour at low temperatures. The prevailing wisdom is that this can be explained by the existence of two-state defects within the material. The so-called standard tunneling model has become the established framework to explain these results, yet it still leaves the central question essentially unanswered -- what are these two-level defects? This question has recently taken on a new urgency with the rise of superconducting circuits in quantum computing, circuit quantum electrodynamics, magnetometry, electrometry and metrology. Superconducting circuits made from aluminium or niobium are fundamentally limited by losses due to two-level defects within the amorphous oxide layers encasing them. On the other hand, these circuits also provide a novel and effective method for studying the very defects which limit their operation. We can now go beyond ensemble measurements and probe individual defects -- observing the quantum nature of their dynamics and studying their formation, their behaviour as a function of applied field, strain, temperature and other properties. This article reviews the plethora of recent experimental results in this area and discusses the various theoretical models which have been used to describe the observations. In doing so, it summarises the current approaches to solving this fundamentally important problem in solid-state physics.Comment: 34 pages, 7 figures, 1 tabl

Current Challenges and Opportunities in Microstructure-Related Properties of Advanced High-Strength Steels

This is a viewpoint paper on recent progress in the understanding of the microstructure–property relations of advanced high-strength steels (AHSS). These alloys constitute a class of high-strength, formable steels that are designed mainly as sheet products for the transportation sector. AHSS have often very complex and hierarchical microstructures consisting of ferrite, austenite, bainite, or martensite matrix or of duplex or even multiphase mixtures of these constituents, sometimes enriched with precipitates. This complexity makes it challenging to establish reliable and mechanism-based microstructure–property relationships. A number of excellent studies already exist about the different types of AHSS (such as dual-phase steels, complex phase steels, transformation-induced plasticity steels, twinning-induced plasticity steels, bainitic steels, quenching and partitioning steels, press hardening steels, etc.) and several overviews appeared in which their engineering features related to mechanical properties and forming were discussed. This article reviews recent progress in the understanding of microstructures and alloy design in this field, placing particular attention on the deformation and strain hardening mechanisms of Mn-containing steels that utilize complex dislocation substructures, nanoscale precipitation patterns, deformation-driven transformation, and twinning effects. Recent developments on microalloyed nanoprecipitation hardened and press hardening steels are also reviewed. Besides providing a critical discussion of their microstructures and properties, vital features such as their resistance to hydrogen embrittlement and damage formation are also evaluated. We also present latest progress in advanced characterization and modeling techniques applied to AHSS. Finally, emerging topics such as machine learning, through-process simulation, and additive manufacturing of AHSS are discussed. The aim of this viewpoint is to identify similarities in the deformation and damage mechanisms among these various types of advanced steels and to use these observations for their further development and maturation.</p