Overlapping Resonances Interference-induced Transparency: The S0→S2/S1S_0 \to S_2/S_1 Photoexcitation Spectrum of Pyrazine

The phenomenon of "overlapping resonances interference-induced transparency" (ORIT) is introduced and studied in detail for the $S_0 \to S_2/S_1$ photoexcitation of cold pyrazine (C$_4$H$_4$N$_2$). In ORIT a molecule becomes transparent at specific wavelengths due to interferences between envelopes of spectral lines displaying overlapping resonances. An example is the $S_2\leftrightarrow S_1$ internal conversion in pyrazine where destructive interference between overlapping resonances causes the $S_0 \to S_2/S_1$ light absorption to disappear at certain wavelengths. ORIT may be of practical importance in multi-component mixtures where it would allow for the selective excitation of some molecules in preference to others. Interference induced cross section enhancement is also shown.Comment: 13 pages, 7 figure

Photoassociation adiabatic passage of ultracold Rb atoms to form ultracold Rb_2 molecules

We theoretically explore photoassociation by Adiabatic Passage of two colliding cold ^{85}Rb atoms in an atomic trap to form an ultracold Rb_2 molecule. We consider the incoherent thermal nature of the scattering process in a trap and show that coherent manipulations of the atomic ensemble, such as adiabatic passage, are feasible if performed within the coherence time window dictated by the temperature, which is relatively long for cold atoms. We show that a sequence of ~2*10^7 pulses of moderate intensities, each lasting ~750 ns, can photoassociate a large fraction of the atomic ensemble at temperature of 100 microkelvin and density of 10^{11} atoms/cm^3. Use of multiple pulse sequences makes it possible to populate the ground vibrational state. Employing spontaneous decay from a selected excited state, one can accumulate the molecules in a narrow distribution of vibrational states in the ground electronic potential. Alternatively, by removing the created molecules from the beam path between pulse sets, one can create a low-density ensemble of molecules in their ground ro-vibrational state.Comment: RevTex, 23 pages, 9 figure

Attacking quantum key distribution with single-photon two-qubit quantum logic

The Fuchs-Peres-Brandt (FPB) probe realizes the most powerful individual attack on Bennett-Brassard 1984 quantum key distribution (BB84 QKD) by means of a single controlled-NOT (CNOT) gate. This paper describes a complete physical simulation of the FPB-probe attack on polarization-based BB84 QKD using a deterministic CNOT constructed from single-photon two-qubit quantum logic. Adding polarization-preserving quantum nondemolition measurements of photon number to this configuration converts the physical simulation into a true deterministic realization of the FPB attack.Comment: 8 pages, 9 figures; references added, 1 new figure, appendix expanded; accepted for publication in Phys. Rev.

Piecewise adiabatic population transfer in a molecule via a wave packet

We propose a class of schemes for robust population transfer between quantum states that utilize trains of coherent pulses and represent a generalized adiabatic passage via a wave packet. We study piecewise Stimulated Raman Adiabatic Passage with pulse-to-pulse amplitude variation, and piecewise chirped Raman passage with pulse-to-pulse phase variation, implemented with an optical frequency comb. In the context of production of ultracold ground-state molecules, we show that with almost no knowledge of the excited potential, robust high-efficiency transfer is possibleComment: 4 pages, 5 figures. Submitted to Phys. Rev. Let

Risk and Return: Consumption versus Market Beta

The interaction between the macroeconomy and asset markets is central to a variety of modern theories of the business cycle. Much recentwork emphasizes the joint nature of the consumption decision and the portfolio allocation decision. In this paper, we compare two formulations of the Capital Asset Pricing Model. The traditional CAPM suggests that the appropriate measure of an asset's risk is the covariance of the asset's return with the market return. The consumption CAPM, on the other hand, implies that a better measure of risk is the covariance with aggregate consumption growth. We examine a cross section of 464 stocks and find that the beta measured with respect to a stock market index outperforms the beta measured with respect to consumption growth.

News or Noise? An Analysis of GNP Revisions

This paper studies the nature of the errors in preliminary GNP data, It first documents that these errors are large. For example, suppose the prelimimary estimate indicates that real GNP did not change over the recent quarter; then one can be only 80 percent confident that the final estimate (annual rate) will be in the range from -2.8 percent to +2.8 percent. The paper also documents that the revisions in GNP data are not forecastable, This finding implies that the preliminary estimates are the efficient given available information. Hence, the Bureau of Economic Analysis appears to follow efficient statistical procedures, in making its preliminary estimates.

Cosmologies with variable parameters and dynamical cosmon: implications on the cosmic coincidence problem

Dynamical dark energy (DE) has been proposed to explain various aspects of the cosmological constant (CC) problem(s). For example, it is very difficult to accept that a strictly constant Lambda-term constitutes the ultimate explanation for the DE in our Universe. It is also hard to acquiesce in the idea that we accidentally happen to live in an epoch where the CC contributes an energy density value right in the ballpark of the rapidly diluting matter density. It should perhaps be more plausible to conceive that the vacuum energy, is actually a dynamical quantity as the Universe itself. More generally, we could even entertain the possibility that the total DE is in fact a mixture of vacuum energy and other dynamical components (e.g. fields, higher order terms in the effective action etc) which can be represented collectively by an effective entity X (dubbed the ``cosmon''). The ``cosmon'', therefore, acts as a dynamical DE component different from the vacuum energy. While it can actually behave phantom-like by itself, the overall DE fluid may effectively appear as standard quintessence, or even mimic at present an almost exact CC behavior. Thanks to the versatility of such cosmic fluid we can show that a composite DE system of this sort (``LXCDM'') may have a key to resolving the mysterious coincidence problem.Comment: LaTeX, 13 pages, 5 figure