Superlattice barrier varactors

SBV (Single Barrier Varactor) diodes have been proposed as alternatives to Schottky barrier diodes for harmonic multiplier applications. However, these show a higher current than expected. The excess current is due to X valley transport in the barrier. We present experimental results showing that the use of a superlattice barrier and doping spikes in the GaAs depletion regions on either side of the barrier can reduce the excess current and improve the control of the capacitance vs. voltage characteristic. The experimental results consist of data taken from two types of device structures. The first test structure was used to study the performance of AlAs/GaAs superlattice barriers. The wafer was fabricated into 90 micron diameter mesa diodes and the resulting current vs. voltage characteristics were measured. A 10 period superlattice structure with a total thickness of approximately 400 A worked well as an electron barrier. The structure had a current density of about one A/sq cm at one volt at room temperature. The capacitance variation of these structures was small because of the design of the GaAs cladding layers. The second test structure was used to study cladding layer designs. These wafers were InGaAs and InAlAs layers lattice matched to an InP substrate. The layers have n(+) doping spikes near the barrier to increase the zero bias capacitance and control the shape of the capacitance vs. voltage characteristic. These structures have a capacitance ratio of 5:1 and an abrupt change from maximum to minimum capacitance. The measurements were made at 80 K. Based on the information obtained from these two structures, we have designed a structure that combines the low current density barrier with the improved cladding layers. The capacitance and current-voltage characteristics from this structure are presented

Costs of meals and parking for parents of hospitalised children in an Australian paediatric hospital

Costs to parents of hospitalised children have been extensively explored, from financial costs to psychological, social and emotional costs. No matter what perspective is taken an admission to hospital of a child means added cost to any family’s budget. For those whose income is dependent on a low wage, or welfare, costs of such an event take up a larger proportion of an income than for families from well-to-do backgrounds. In this paper, we explore the potential impact on a family budget of costs of parking and meals incurred during a child’s admission to hospital.To determine costs, a survey was conducted at food outlets to examine types and availability of meals, opening times, proximity to wards and the cost of average types of meals on offer at different facilities. Costs of parking were determined. We took income figures for a family from the website of the Australian Bureau of Statistics (ABS). An estimate of the costs of food and parking to support one parent to remain with the child was at least 30% of the average weekly family disposable income. For one-parent families, their income is significantly proportionally depleted by covering costs of food and parking for an accompanying parent. We recommend that parents be provided with meals whilst staying with their hospitalised child; that provision be made to allow families to eat together and that free parking be made available to all parents

Calibration of the HemoCue point-of-care analyser for determining haemoglobin concentration in a lizard and a fish

Haemoglobin concentration ([Hb]) is measured for a wide variety of animal studies. The use of point-of-care devices, such as the HemoCue, is becoming increasingly common because of their portability, relative ease of use and low cost. In this study, we aimed to determine whether the [Hb] of blue-tongued skink (Tiliqua nigrolutea) blood can be determined accurately using the HemoCue and whether the HemoCue overestimates the [Hb] of reptile blood in a similar manner to fish blood. Additionally, we aimed to test whether ploidy affected [Hb] determined by the HemoCue using blood from diploid and triploid Atlantic salmon (Salmo salar). The HemoCue Hb 201⁺ systematically overestimated [Hb] in both blue-tongued skinks and Atlantic salmon, and there was no difference between calibration equations determined for diploid or triploid salmon. The overestimation was systematic in both species and, as such, [Hb] determined by the HemoCue can be corrected using appropriate calibration equations

Raman Quantum Memory with Built-In Suppression of Four-wave Mixing Noise

Quantum memories are essential for large-scale quantum information networks. Along with high efficiency, storage lifetime and optical bandwidth, it is critical that the memory add negligible noise to the recalled signal. A common source of noise in optical quantum memories is spontaneous four-wave mixing. We develop and implement a technically simple scheme to suppress this noise mechanism by means of quantum interference. Using this scheme with a Raman memory in warm atomic vapour we demonstrate over an order of magnitude improvement in noise performance. Furthermore we demonstrate a method to quantify the remaining noise contributions and present a route to enable further noise suppression. Our scheme opens the way to quantum demonstrations using a broadband memory, significantly advancing the search for scalable quantum photonic networks.Comment: 6 pages, 5 figures plus Supplementary Materia

Theory of noise suppression in {\Lambda}-type quantum memories by means of a cavity

Quantum memories, capable of storing single photons or other quantum states of light, to be retrieved on-demand, offer a route to large-scale quantum information processing with light. A promising class of memories is based on far-off-resonant Raman absorption in ensembles of $\Lambda$-type atoms. However at room temperature these systems exhibit unwanted four-wave mixing, which is prohibitive for applications at the single-photon level. Here we show how this noise can be suppressed by placing the storage medium inside a moderate-finesse optical cavity, thereby removing the main roadblock hindering this approach to quantum memory.Comment: 10 pages, 3 figures. This paper provides the theoretical background to our recent experimental demonstration of noise suppression in a cavity-enhanced Raman-type memory ( arXiv:1510.04625 ). See also the related paper arXiv:1511.05448, which describes numerical modelling of an atom-filled cavity. Comments welcom

High-speed noise-free optical quantum memory

Quantum networks promise to revolutionise computing, simulation, and communication. Light is the ideal information carrier for quantum networks, as its properties are not degraded by noise in ambient conditions, and it can support large bandwidths enabling fast operations and a large information capacity. Quantum memories, devices that store, manipulate, and release on demand quantum light, have been identified as critical components of photonic quantum networks, because they facilitate scalability. However, any noise introduced by the memory can render the device classical by destroying the quantum character of the light. Here we introduce an intrinsically noise-free memory protocol based on two-photon off-resonant cascaded absorption (ORCA). We consequently demonstrate for the first time successful storage of GHz-bandwidth heralded single photons in a warm atomic vapour with no added noise; confirmed by the unaltered photon statistics upon recall. Our ORCA memory platform meets the stringent noise-requirements for quantum memories whilst offering technical simplicity and high-speed operation, and therefore is immediately applicable to low-latency quantum networks