Electronic structure calculations were performed using DFT and high-level ab initio methods to understand the role of atomic halogens in the transformation of gaseous mercury in the Arctic atmosphere. The latter methods were found to be superior in reproducing the reaction enthalpies as well as the geometrical parameters and vibrational frequencies, and therefore they were employed to calculate the energy potentials for the capture-deactivation approach to study the kinetics of halogen-mercury atomic recombination. Using the calculated rate constants and inferred concentrations of halogen atoms in the Arctic troposphere, we found that atomic bromine might be responsible for the mercury depletion episodes

A second-order nonlinearity has been proposed as a way to perform a conditional phase gate between two photons. The process involves combining the two photons into a single one (parametric up-conversion) and subsequently splitting that one into two photons identical to the original ones (parametric down-conversion), except for an overall phase shift. We show here that, when the multimode nature of the initial photon wavepackets is considered, this approach suffers from the same difficulties as the third-order (Kerr-based) methods: specifically, the final state of the photons is inevitably spectrally distorted and entangled. The maximum fidelity appears to be limited to F < 0.4 for a free-space configuration, but we find that this could theoretically be pushed to F ≃ 0.6 if the nonlinear medium is placed in an optical cavity. We show analytically that this latter result is identical to what one would obtain from a third-order nonlinear medium in the same arrangement.

Theory Theory C 1000 A Theoretical Study on the Reactions of Hg with Halogens: Atmospheric Implications. -(KHALIZOV*, A. F.; VISWANATHAN, B.; LARREGARAY, P.; ARIYA, P. A.; J. Phys. Chem. A 107 (2003) 33, 6360-6365; Dep. Chem., McGill Univ., Montreal, Que. H3A 2K6, Can.; Eng.) -Schramke 43-005

It has been suggested that second-order nonlinearities could be used for quantum logic at the single-photon level. Specifically, successive two-photon processes in principle could accomplish the phase shift (conditioned on the presence of two photons in the low frequency modes) |011 −→ |100 −→ −|011 . We have analyzed a recent scheme proposed by Xia et al. to induce such a conditional phase shift between two single-photon pulses propagating at different speeds through a nonlinear medium with a nonlocal response. We present here an analytical solution for the most general case, i.e. for an arbitrary response function, initial state, and pulse velocity, which supports their numerical observation that a π phase shift with unit fidelity is possible, in principle, in an appropriate limit. We also discuss why this is possible in this system, despite the theoretical objections to the possibility of conditional phase shifts on single photons that were raised some time ago by Shapiro and by one of us. II. OBSTACLES TO HIGH-FIDELITY SINGLE-PHOTON NONLINEAR OPTICSThe main obstacles to achieving high-fidelity in nonlinear optical processes at the single-photon level identified in refs.[3] and [6] are:

Quantum imaging with undetected photons (QIUP) is a unique method of image acquisition where the photons illuminating the object are not detected. This method relies on quantum interference and spatial correlations between the twin photons to form an image. Here we present a detailed study of the resolution limits of position correlation enabled QIUP. We establish a quantitative relation between the spatial resolution and the twin-photon position correlation. Furthermore, we also quantitatively establish the roles that the wavelength of the undetected illumination field and the wavelength of the detected field play in the resolution. Like ghost imaging and unlike conventional imaging, the resolution limit imposed by the spatial correlation between the twin photons in QIUP cannot be further improved by conventional optical techniques.

Quantum imaging with undetected photons (QIUP) is a unique imaging technique that does not require the detection of the light used for illuminating the object. This technique requires a correlated pair of photons. In the existing implementations of QIUP, the imaging is enabled by the momentum correlation between the twin photons. We investigate the complementary scenario in which the imaging is instead enabled by the position correlation between the two photons. We present a general theory and show that the properties of the images obtained in these two cases are significantly distinct.

High-resolution Fourier transform spectrometer sunspot umbral spectra obtained at the National Solar Observatory/Kitt Peak were used to identify molecular rotational lines arising from the infrared band systems of CrH and CrD molecules. Measurement of the equivalent width used the Gaussian-profile approximation method, which is suitable especially for faint lines. Equivalent widths are measured for an adequate number of best lines of the A -X (0, 0) band of CrH and the A -X (0, 0; 1, 0) bands of CrD and, thereby, the effective rotational temperatures are estimated.

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