Abnormalities of the retinal cone system in retinitis pigmentosa

AbstractPatients with retinitis pigmentosa (RP) show delayed inner retinal responses as measured by the cone ERG response to a 30 Hz stimulus. To determine the extent to which this delay results from abnormalities of cone phototransduction, cone ERGs to single flashes were obtained from 21 patients with RP and a model of cone phototransduction was fitted to the leading edge of the a-waves of these ERGs. Nearly all patients showed an abnormally low sensitivity of cone phototransduction consistent with a reduction in the amplification of transduction. This abnormality can account for part of the delayed 30 Hz response. Analysis of post-receptoral potentials indicated that RP also slows the responses of the inner retina. A combination of these two factors, a sensitivity change at the receptor and a delay in the response of the inner retina, produces the delayed response of the cone flicker ERG in patients with RP

Conditional evolution in single-atom cavity QED

We consider a typical setup of cavity QED consisting of a two-level atom interacting strongly with a single resonant electromagnetic field mode inside a cavity. The cavity is resonantly driven and the output undergoes continuous homodyne measurements. We derive an explicit expression for the state of the system conditional on a discrete photocount record. This expression takes a particularly simple form if the system is initially in the steady state. As a byproduct, we derive a general formula for the steady state that had been conjectured before in the strong driving limit.Comment: 15 pages, 1 postscript figure, added discussion of mode

Coherent generation of EPR-entangled light pulses mediated by a single trapped atom

We show that a single, trapped, laser-driven atom in a high-finesse optical cavity allows for the quantum-coherent generation of entangled light pulses on demand. Schemes for generating simultaneous and temporally separated pulse pairs are proposed. The mechanical effect of the laser excitation on the quantum motion of the cold trapped atom mediates the entangling interaction between two cavity modes and between the two subsequent pulses, respectively. The entanglement is of EPR-type, and its degree can be controlled through external parameters. At the end of the generation process the atom is decorrelated from the light field. Possible experimental implementations of the proposals are discussed.Comment: 11 pages, 4 figure

On the suppression of the diffusion and the quantum nature of a cavity mode. Optical bistability; forces and friction in driven cavities

A new analytical method is presented here, offering a physical view of driven cavities where the external field cannot be neglected. We introduce a new dimensionless complex parameter, intrinsically linked to the cooperativity parameter of optical bistability, and analogous to the scaled Rabbi frequency for driven systems where the field is classical. Classes of steady states are iteratively constructed and expressions for the diffusion and friction coefficients at lowest order also derived. They have in most cases the same mathematical form as their free-space analog. The method offers a semiclassical explanation for two recent experiments of one atom trapping in a high Q cavity where the excited state is significantly saturated. Our results refute both claims of atom trapping by a quantized cavity mode, single or not. Finally, it is argued that the parameter newly constructed, as well as the groundwork of this method, are at least companions of the cooperativity parameter and its mother theory. In particular, we lay the stress on the apparently more fundamental role of our structure parameter.Comment: 24 pages, 7 figures. Submitted to J. Phys. B: At. Mol. Opt. Phy

Trapping of Single Atoms with Single Photons in Cavity QED

Two recent experiments have reported the trapping of individual atoms inside optical resonators by the mechanical forces associated with single photons [Hood et al., Science 287, 1447 (2000) and Pinkse et al., Nature 404, 365 (2000)]. Here we analyze the trapping dynamics in these settings, focusing on two points of interest. Firstly, we investigate the extent to which light-induced forces in these experiments are distinct from their free-space counterparts. Secondly, we explore the quantitative features of the resulting atomic motion and how these dynamics are mapped onto variations of the intracavity field. Not surprisingly, qualitatively distinct atomic dynamics arise as the coupling and dissipative rates are varied. For the experiment of Hood et al., we show that atomic motion is largely conservative and is predominantly in radial orbits transverse to the cavity axis. A comparison with the free-space theory demonstrates that the fluctuations of the dipole force are suppressed by an order of magnitude. This effect is based upon the Jaynes-Cummings eigenstates of the atom-cavity system and represents qualitatively new physics for optical forces at the single-photon level. By contrast, even in a regime of strong coupling in the experiment of Pinkse et al., there are only small quantitative distinctions between the free-space theory and the quantum theory, so it is not clear that description of this experiment as a novel single-quantum trapping effect is necessary. The atomic motion is strongly diffusive, leading to an average localization time comparable to the time for an atom to transit freely through the cavity and to a reduction in the ability to infer aspects of the atomic motion from the intracavity photon number.Comment: 19 pages, 22 figure files, REVTEX, corrected spelling, LaTeX now produces postscript which includes figures, minor changes to figures. Final version to be published in Physical Review A, expanded summary of results in introduction, minor changes to figures and tex

A Comparison of Domestic Water Heating Options in the Austin Electric Service Area

This report examines the energy, demand, and economic effects of three alternative electric water heating systems from the perspective of both the City of Austin Electric Utility and its ratepayers. An hourly computer simulation was used to model the operation of (1) a conventional electric resistance water heater (ERWH), (2) a heat pump water heater (HPWH), and (3) a heat recovery water heater (HRWH). Data from a previously conducted field test of solar water heaters (SWH) in the Austin area was used to compare this fourth water heating option. In the base case, the SWH was found to save the most energy relative to a conventional ERWH followed by the HPWH and the HRWH, respectively. However, under most economic assumptions thought to be reasonable for the Austin area, the heat recovery water heater appeared to be the best choice for the Austin all-electric ratepayer. From the Utility's perspective, it was determined that: (1) widespread ratepayer use of heat recovery water heater systems would be beneficial to the Utility; (2) ratepayer use of solar water heater systems would be marginally beneficial to the Utility; and (3) ratepayer use of heat pump water heater systems would not be beneficial to the Utility

Collective Sideband Cooling in an Optical Ring Cavity

We propose a cavity based laser cooling and trapping scheme, providing tight confinement and cooling to very low temperatures, without degradation at high particle densities. A bidirectionally pumped ring cavity builds up a resonantly enhanced optical standing wave which acts to confine polarizable particles in deep potential wells. The particle localization yields a coupling of the degenerate travelling wave modes via coherent photon redistribution. This induces a splitting of the cavity resonances with a high frequency component, that is tuned to the anti-Stokes Raman sideband of the particles oscillating in the potential wells, yielding cooling due to excess anti-Stokes scattering. Tight confinement in the optical lattice together with the prediction, that more than 50% of the trapped particles can be cooled into the motional ground state, promise high phase space densities.Comment: 4 pages, 1 figur

Two-atom dark states in electromagnetic cavities

The center-of-mass motion of two two-level atoms coupled to a single damped mode of an electromagnetic resonator is investigated. For the case of one atom being initially excited and the cavity mode in the vacuum state it is shown that the atomic time evolution is dominated by the appearance of dark states. These states, in which the initial excitation is stored in the internal atomic degrees of freedom and the atoms become quantum mechanically entangled, are almost immune against photon loss from the cavity. Various properties of the dark states within and beyond the Raman-Nath approximation of atom optics are worked out.Comment: 8 pages, 4 figure