Development threshold, capital flows, and financial turbulence

We study capital flows in a panel of 130 countries, and derive the implications for the observed patterns of capital flows and capital controls before and into the crisis of 2008–11. We find that the size of capital flows is positively correlated with country's income level. In addition, capital flight has a non-linear relationship with the income level. Using the Hansen threshold estimation, we identify a three-stage threshold effect: for low-income countries (GDP per capita below US$3,000), capital flight increases as the income level rises; and only after the economy passes a threshold level (GDP per capita above US$ 5,000), capital flight declines with income. We conclude with a case study of Brazil and Korea, observing that the decisions to implement capital control measures tend to be pushed around by the feedbacks among economic growth, currency appreciation, and the global financial conditions

Sensing Coherent Phonons with Two-photon Interference

Detecting coherent phonons pose different challenges compared to coherent photons due to the much stronger interaction between phonons and matter. This is especially true for high frequency heat carrying phonons, which are intrinsic lattice vibrations experiencing many decoherence events with the environment, and are thus generally assumed to be incoherent. Two photon interference techniques, especially coherent population trapping (CPT) and electromagnetically induced transparency (EIT), have led to extremely sensitive detection, spectroscopy and metrology. Here, we propose the use of two photon interference in a three level system to sense coherent phonons. Unlike prior works which have treated phonon coupling as damping, we account for coherent phonon coupling using a full quantum-mechanical treatment. We observe strong asymmetry in absorption spectrum in CPT and negative dispersion in EIT susceptibility in the presence of coherent phonon coupling which cannot be accounted for if only pure phonon damping is considered. Our proposal has application in sensing heat carrying coherent phonons effects and understanding coherent bosonic multi-pathway interference effects in three coupled oscillator systems

Coherent Exciton Lasing in ZnSe/ZnCdSe Quantum Wells?

A new mechanism for exciton lasing in ZnSe/ZnCdSe quantum wells is proposed. Lasing, occurring below the lowest exciton line, may be associated with a BCS-like condensed (coherent) exciton state. This state is most stable at low temperatures for densities in the transition region separating the exciton Bose gas and the coherent exciton state. Calculations show the gain region to lie below the exciton line and to be separated from the absorption regime by a transparency region of width, for example, about 80 meV for a 90 Angstrom ZnSe/Zn_(0.75)Cd_(0.25)Se quantum well. Experimental observation of the transparency region using differential spectroscopy would confirm this picture.Comment: 9 pages + 3 figs contained in 4 postscript files to appear Appl. Phys. Lett. March 13, 199