The effects of water impinging on thermally controlled surfaces under space conditions

Analysis of monochromatic reflectance changes due to impinging water spray from sharp-edge nozzles on thermally-controlled paints under space condition

Signatures of the collapse and revival of a spin Schr\"{o}dinger cat state in a continuously monitored field mode

We study the effects of continuous measurement of the field mode during the collapse and revival of spin Schr\"{o}dinger cat states in the Tavis-Cummings model of N qubits (two-level quantum systems) coupled to a field mode. We show that a compromise between relatively weak and relatively strong continuous measurement will not completely destroy the collapse and revival dynamics while still providing enough signal-to-noise resolution to identify the signatures of the process in the measurement record. This type of measurement would in principle allow the verification of the occurrence of the collapse and revival of a spin Schr\"{o}dinger cat state.Comment: 5 pages, 2 figure

Cool for Cats

The iconic Schr\"odinger's cat state describes a system that may be in a superposition of two macroscopically distinct states, for example two clearly separated oscillator coherent states. Quite apart from their role in understanding the quantum classical boundary, such states have been suggested as offering a quantum advantage for quantum metrology, quantum communication and quantum computation. As is well known these applications have to face the difficulty that the irreversible interaction with an environment causes the superposition to rapidly evolve to a mixture of the component states in the case that the environment is not monitored. Here we show that by engineering the interaction with the environment there exists a large class of systems that can evolve irreversibly to a cat state. To be precise we show that it is possible to engineer an irreversible process so that the steady state is close to a pure Schr\"odinger's cat state by using double well systems and an environment comprising two-photon (or phonon) absorbers. We also show that it should be possible to prolong the lifetime of a Schr\"odinger's cat state exposed to the destructive effects of a conventional single-photon decohering environment. Our protocol should make it easier to prepare and maintain Schr\"odinger cat states which would be useful in applications of quantum metrology and information processing as well as being of interest to those probing the quantum to classical transition.Comment: 10 pages, 7 figures. Significantly updated version with supplementary informatio

Estimating the Welfare Effects of Digital Infrastructure

While much economic policy presumes that more information infrastructure yields higher economic returns, little empirical work measures the magnitudes of these returns. We examine investment by local exchange telephone companies in fiber optic cable, ISDN lines and signal seven software, infrastructure which plays an essential role in bringing digital technology to local telephone networks. We estimate the elasticity of the derived demand for infrastructure investment faced by local exchange companies, controlling for factors such as local economic activity and the political disposition of state regulators. Our model postulates a regulated profit maximizing local exchange firm and a regulatory agency with predetermined political leanings in favor of consumer prices or firm profits. The model accounts for variation in state regulation and local economic conditions. In all our estimates we find that consumer demand is sensitive to investment in modern infrastructure, particularly as represented by fiber optic cable. Our estimates imply that infrastructure investment is responsible for a substantial fraction of the recent growth in consumer surplus and business revenue in local telecommunication services.

The quantum-classical crossover of a field mode

We explore the quantum-classical crossover in the behaviour of a quantum field mode. The quantum behaviour of a two-state system - a qubit - coupled to the field is used as a probe. Collapse and revival of the qubit inversion form the signature for quantum behaviour of the field and continuous Rabi oscillations form the signature for classical behaviour of the field. We demonstrate both limits in a single model for the full coupled system, for states with the same average field strength, and so for qubits with the same Rabi frequency.Comment: 6 pages, 3 figures (in this version the figures, text and references have all been expanded

Overcoming decoherence in the collapse and revival of spin Schr\"odinger cats

In addition to being a very interesting quantum phenomenon, Schr\"odinger cat swapping has the potential for application in the preparation of quantum states that could be used in metrology and other quantum processing. We study in detail the effects of field decoherence on a cat-swapping system comprising a set of identical qubits, or spins, all coupled to a field mode. We demonstrate that increasing the number of spins actually mitigates the effects of field decoherence on the collapse and revival of a spin Schr\"odinger cat, which could be of significant utility in quantum metrology and other quantum processing.Comment: 4 pages, 2 figure

Towards a complete, continuous, Wigner function for an ensemble of spins or qubits

We present a new quasi-probability distribution function for ensembles of spin-half particles or qubits that has many properties in common with Wigner's original function for systems of continuous variables. We show that this function provides clear and intuitive graphical representation of a wide variety of states, including Fock states, spin-coherent states, squeezed states, superpositions and statistical mixtures. Unlike previous attempts to represent ensembles of spins/qubits, this distribution is capable of simultaneously representing several angular momentum shells.Comment: 11 pages, 6 figures. If viewed in adobe reader all figures except Fig 2 are interactive. For the non-interactive figures corresponding to those of the published version of this work please see version one of this preprint (which is also a much smaller file

From quantum trajectories to classical orbits

Recently it has been shown that the evolution of open quantum systems may be ``unraveled'' into individual ``trajectories,'' providing powerful numerical and conceptual tools. In this letter we use quantum trajectories to study mesoscopic systems and their classical limit. We show that in this limit, Quantum Jump (QJ) trajectories approach a diffusive limit very similar to the Quantum State Diffusion (QSD) unraveling. The latter follows classical trajectories in the classical limit. Hence, both unravelings show the rise of classical orbits. This is true for both regular and chaotic systems (which exhibit strange attractors).Comment: 7 pages RevTeX 3.0 + 2 figures (postscript). Submitted to Physical Review Letter