Polarization squeezing by optical Faraday rotation

We show that it is possible to generate continuous-wave fields and pulses of polarization squeezed light by sending classical, linearly polarized laser light twice through an atomic sample which causes an optical Faraday rotation of the field polarization. We characterize the performance of the process, and we show that an appreciable degree of squeezing can be obtained under realistic physical assumptions.Comment: 4 pages, 4 figure

The impact of contextual factors on the predicted bulk water pipe repair times in Wellington City : a thesis presented in partial fulfilment of the requirements for the degree of Master in Emergency Management at Massey University, Wellington, New Zealand

Lifelines, like the water supply, are essential for the survival of people, communities, and businesses. In the event of a significant natural disaster, like an earthquake, it can be expected that these regional lifelines will be severely damaged. Wellington, the capital of New Zealand, contains many lifelines that are highly vulnerable to failure. The water supply is especially susceptible, as it crosses the Wellington Fault multiple times and carries water through landslide prone corridors. Because of the risk, and potential impact on people, several predictive models have been created to calculate the likely downtimes so individuals and organisations can prepare for the loss. Many of these predictive models are comprehensive in what they calculate. However, they require improvement as they do not include local and contextual factors or the influence of other lifelines. For example, they do not include the impact of staff logistics, assume access to required equipment is a given, and ignore interdependencies between lifelines, such as the loss of access to repair sites because of damage to the transportation network. This research aims to improve these current models by investigating the magnitude of these site-specific and interdependency factors. Following a sequential mixed methods approach and using a pragmatic viewpoint, experts directly involved in the repair and maintenance of lifelines were selected for interviews. In total 20 professionals were contacted using a snowball and convenience sampling technique. Out of these 20, five were available for in-depth semi-structured phone interviews. From these interviews, anything stated to affect the repair times was highlighted, the most prominent of which were incorporated into current predictive models and their influence on repair times calculated. In total 12 different issues were discussed, 4 of which were examined further. These factors were: staff logistical problems; the slope of the land affecting damage inspection processes; the impact of uncommon pipe diameters on the repair process; and access problems. Once identified, these factors were incorporated into current predictive models, and the impact on repair times calculated. By including these contextual influences, it was found that they increased repair times by between 3 and 13 days depending on the water source and 31 and 111 days when incorporating the influence of landslides. Thus, proving contextual influences have a significant impact on repair times. Overall this study 1) revealed the importance of including contextual factors into predictive calculations and 2) created more accurate downtime predictions for the water supply in Wellington City, allowing for people, organisations, and planners to better prepare for the potential risk

Deterministic atom-light quantum interface

The notion of an atom-light quantum interface has been developed in the past decade, to a large extent due to demands within the new field of quantum information processing and communication. A promising type of such interface using large atomic ensembles has emerged in the past several years. In this article we review this area of research with a special emphasis on deterministic high fidelity quantum information protocols. Two recent experiments, entanglement of distant atomic objects and quantum memory for light are described in detail.Comment: 50 pages (bookstyle) 15 graphs, to be published in "Advances in Atomic, Molecular, and Optical Physics" Vol. 54. (2006)(Some of the graphs here have lower resolution than in the version to be published

Distant Entanglement of Macroscopic Gas Samples

One of the main ingredients in most quantum information protocols is a reliable source of two entangled systems. Such systems have been generated experimentally several years ago for light but has only in the past few years been demonstrated for atomic systems. None of these approaches however involve two atomic systems situated in separate environments. This is necessary for the creation of entanglement over arbitrary distances which is required for many quantum information protocols such as atomic teleportation. We present an experimental realization of such distant entanglement based on an adaptation of the entanglement of macroscopic gas samples containing about 10^11 cesium atoms shown previously by our group. The entanglement is generated via the off-resonant Kerr interaction between the atomic samples and a pulse of light. The achieved entanglement distance is 0.35m but can be scaled arbitrarily. The feasibility of an implementation of various quantum information protocols using macroscopic samples of atoms has therefore been greatly increased. We also present a theoretical modeling in terms of canonical position and momentum operators X and P describing the entanglement generation and verification in presence of decoherence mechanisms.Comment: 20 pages book-style, 3 figure

Dynamical effects of exchange symmetry breaking in mixtures of interacting bosons

In a double-well potential, a Bose-Einstein condensate exhibits Josephson oscillations or self-trapping, depending on its initial preparation and on the ratio of inter-particle interaction to inter-well tunneling. Here, we elucidate the role of the exchange symmetry for the dynamics with a mixture of two distinguishable species with identical physical properties, i.e. which are governed by an isospecific interaction and external potential. In the mean-field limit, the spatial population imbalance of the mixture can be described by the dynamics of a single species in an effective potential with modified properties or, equivalently, with an effective total particle number. The oscillation behavior can be tuned by populating the second species while maintaining the spatial population imbalance and all other parameters constant. In the corresponding many-body approach, the single-species description approximates the full counting statistics well also outside the realm of spin-coherent states. The method is extended to general Bose-Hubbard systems and to their classical mean-field limits, which suggests an effective single-species description of multicomponent Bose gases with weakly an-isospecific interactions.Comment: amended and expanded, accepted for Phys. Rev. A, 14 pages, 7 figure