Field Quantization, Photons and Non-Hermitean Modes

Field quantization in three dimensional unstable optical systems is treated by expanding the vector potential in terms of non-Hermitean (Fox-Li) modes in both the cavity and external regions. The cavity non-Hermitean modes (NHM) are treated using the paraxial and monochromaticity approximations. The NHM bi-orthogonality relationships are used in a standard canonical quantization procedure based on introducing generalised coordinates and momenta for the electromagnetic (EM) field. The quantum EM field is equivalent to a set of quantum harmonic oscillators (QHO), associated with either the cavity or the external region NHM. This confirms the validity of the photon model in unstable optical systems, though the annihilation and creation operators for each QHO are not Hermitean adjoints. The quantum Hamiltonian for the EM field is the sum of non-commuting cavity and external region contributions, each of which is sum of independent QHO Hamiltonians for each NHM, but the external field Hamiltonian also includes a coupling term responsible for external NHM photon exchange processes. Cavity energy gain and loss processes is associated with the non-commutativity of cavity and external region operators, given in terms of surface integrals involving cavity and external region NHM functions on the cavity-external region boundary. The spontaneous decay of a two-level atom inside an unstable cavity is treated using the essential states approach and the rotating wave approximation. Atomic transitions leading to cavity NHM photon absorption have a different coupling constant to those leading to photon emission, a feature resulting from the use of NHM functions. Under certain conditions the decay rate is enhanced by the Petermann factor.Comment: 38 pages, tex, 2 figures, ps. General expression for decay rate added. To be published in Journal of Modern Optic

Decay of highly-correlated spin states in a dipolar-coupled solid

We have measured the decay of NMR multiple quantum coherence intensities both under the internal dipolar Hamiltonian as well as when this interaction is effectively averaged to zero, in the cubic calcium fluoride (CaF2) spin system and the pseudo one-dimensional system of fluoroapatite. In calcium fluoride the decay rates depend both on the number of correlated spins in the cluster, as well as on the coherence number. For smaller clusters, the decays depend strongly on coherence number, but this dependence weakens as the size of the cluster increases. The same scaling was observed when the coherence distribution was measured in both the usual Zeeman or z basis and the x basis. The coherence decay in the one dimensional fluoroapatite system did not change significantly as a function of the multiple quantum growth time, in contrast to the calcium fluoride case. While the growth of coherence orders is severely restricted in this case, the number of correlated spins should continue to grow, albeit more slowly. All coherence intensities were observed to decay as Gaussian functions in time. In all cases the standard deviation of the observed decay appeared to scale linearly with coherence number.Comment: 7 pages, 9 figures. submitted to PR

Radio Galaxy Clustering at z~0.3

Radio galaxies are uniquely useful as probes of large-scale structure as their uniform identification with giant elliptical galaxies out to high redshift means that the evolution of their bias factor can be predicted. As the initial stage in a project to study large-scale structure with radio galaxies we have performed a small redshift survey, selecting 29 radio galaxies in the range 0.19<z<0.45 from a contiguous 40 square degree area of sky. We detect significant clustering within this sample. The amplitude of the two-point correlation function we measure is consistent with no evolution from the local (z<0.1) value. This is as expected in a model in which radio galaxy hosts form at high redshift and thereafter obey a continuity equation, although the signal:noise of the detection is too low to rule out other models. Larger surveys out to z~1 should reveal the structures of superclusters at intermediate redshifts and strongly constrain models for the evolution of large-scale structure.Comment: 7 pages, 3 figures, accepted by ApJ Letter

Atmospheric and Oceanographic Information Processing System (AOIPS) system description

The development of hardware and software for an interactive, minicomputer based processing and display system for atmospheric and oceanographic information extraction and image data analysis is described. The major applications of the system are discussed as well as enhancements planned for the future

Single-shot optical conductivity measurement of dense aluminum plasmas

The optical conductivity of a dense femtosecond laser-heated aluminum plasma heated to 0.1-1.5 eV was measured using frequency-domain interferometry with chirped pulses, permitting simultaneous observation of optical probe reflectivity and probe pulse phase shift. Coupled with published models of bound-electron contributions to the conductivity, these two independent experimental data yielded a direct measurement of both real and imaginary components of the plasma conductivity.DOE National Nuclear Security Administration DE-FC52-03NA00156Physic

Decoherence Rates in Large Scale Quantum Computers and Macroscopic Systems

Markovian regime decoherence effects in quantum computers are studied in terms of the fidelity for the situation where the number of qubits N becomes large. A general expression giving the decoherence time scale in terms of Markovian relaxation elements and expectation values of products of system fluctuation operators is obtained, which could also be applied to study decoherence in other macroscopic systems such as Bose condensates and superconductors. A standard circuit model quantum computer involving three-state lambda system ionic qubits is considered, with qubits localised around well-separated positions via trapping potentials. The centre of mass vibrations of the qubits act as a reservoir. Coherent one and two qubit gating processes are controlled by time dependent localised classical electromagnetic fields that address specific qubits, the two qubit gating processes being facilitated by a cavity mode ancilla, which permits state interchange between qubits. With a suitable choice of parameters, it is found that the decoherence time can be made essentially independent of N.Comment: Minor revisions. To be published in J Mod Opt. One figur

The Effect of Hot Gas in WMAP's First Year Data

By cross-correlating templates constructed from the 2 Micron All Sky Survey (2MASS) Extended Source (XSC) catalogue with WMAP's first year data, we search for the thermal Sunyaev-Zel'dovich signature induced by hot gas in the local Universe. Assuming that galaxies trace the distribution of hot gas, we select regions on the sky with the largest projected density of galaxies. Under conservative assumptions on the amplitude of foreground residuals, we find a temperature decrement of -35 $\pm$ 7 $\mu$K ($\sim 5\sigma$ detection level, the highest reported so far) in the $\sim$ 26 square degrees of the sky containing the largest number of galaxies per solid angle. We show that most of the reported signal is caused by known galaxy clusters which, when convolved with the average beam of the WMAP W band channel, subtend a typical angular size of 20--30 arcmins. Finally, after removing from our analyses all pixels associated with known optical and X-ray galaxy clusters, we still find a tSZ decrement of -96 $\pm$ 37 $\mu$K in pixels subtending about $\sim$ 0.8 square degrees on the sky. Most of this signal is coming from five different cluster candidates in the Zone of Avoidance (ZoA), present in the Clusters In the ZoA (CIZA) catalogue. We found no evidence that structures less bound than clusters contribute to the tSZ signal present in the WMAP data.Comment: 10 pages, 4 figures, matches accepted version in ApJ Letter

Asymmetric double-well potential for single atom interferometry

We consider the evolution of a single-atom wavefunction in a time-dependent double-well interferometer in the presence of a spatially asymmetric potential. We examine a case where a single trapping potential is split into an asymmetric double well and then recombined again. The interferometer involves a measurement of the first excited state population as a sensitive measure of the asymmetric potential. Based on a two-mode approximation a Bloch vector model provides a simple and satisfactory description of the dynamical evolution. We discuss the roles of adiabaticity and asymmetry in the double-well interferometer. The Bloch model allows us to account for the effects of asymmetry on the excited state population throughout the interferometric process and to choose the appropriate splitting, holding and recombination periods in order to maximize the output signal. We also compare the outcomes of the Bloch vector model with the results of numerical simulations of the multi-state time-dependent Schroedinger equation.Comment: 9 pages, 6 figure

Theory of Pseudomodes in Quantum Optical Processes

This paper deals with non-Markovian behaviour in atomic systems coupled to a structured reservoir of quantum EM field modes, with particular relevance to atoms interacting with the field in high Q cavities or photonic band gap materials. In cases such as the former, we show that the pseudo mode theory for single quantum reservoir excitations can be obtained by applying the Fano diagonalisation method to a system in which the atomic transitions are coupled to a discrete set of (cavity) quasimodes, which in turn are coupled to a continuum set of (external) quasimodes with slowly varying coupling constants and continuum mode density. Each pseudomode can be identified with a discrete quasimode, which gives structure to the actual reservoir of true modes via the expressions for the equivalent atom-true mode coupling constants. The quasimode theory enables cases of multiple excitation of the reservoir to now be treated via Markovian master equations for the atom-discrete quasimode system. Applications of the theory to one, two and many discrete quasimodes are made. For a simple photonic band gap model, where the reservoir structure is associated with the true mode density rather than the coupling constants, the single quantum excitation case appears to be equivalent to a case with two discrete quasimodes