One-step error correction for multipartite polarization entanglement

We present two economical one-step error-correction protocols for multipartite polarization-entangled systems in a Greenberger-Horne-Zeilinger state. One uses spatial entanglement to correct errors in the polarization entanglement of an N-photon system, resorting to linear optical elements. The other uses frequency entanglement to correct errors in the polarization entanglement of an N-photon system. The parties in quantum communication can obtain a maximally entangled state from each N-photon system transmitted with one step in these two protocols, and both of their success probabilities are 100%, in principle. That is, they both work in a deterministic way, and they do not largely consume the less-entangled photon systems, which is far different from conventional multipartite entanglement purification schemes. These features may make these two protocols more useful for practical applications in long-distance quantum communication.Comment: 8 pages, 2 figure

Assessing the Effects of NAFTA ON Canada/US Agricultural Trade

While there seems to be an agreement that Canada-US Free Trade Agreement (CUSTA)/North American Free Trade Agreement (NAFTA) have benefited member countries, some analysts have argued that the agreements had little effect on the bilateral Canada/US agricultural trade as many other factors have contributed to the increased trade flows. Results from this study reveal that the aggregate bilateral agricultural trade flows have generally experienced a steady growth since the implementation of NAFTA with trade flows seemingly favoring Canada more than the US since 1992. At the industry level, the impacts of NAFTA on Canada/US agricultural trade were varied with the sub-sectors analyzed responding differently to the bilateral trade liberalization.CUSTA/NAFTA, agricultural trade, liberalization, integration, trade flows, International Relations/Trade,

Quantum non-demolition measurement of microwave photons using engineered quadratic interactions

We present a quantum electrical circuit with Josephson junctions formed of two anharmonic oscillators coupled with an interaction $g\gamma_{1}^{2}\gamma_{2}^{2}$ where $\gamma_{1}$ and $\gamma_{2}$ are position-like coordinates. This type of coupling allows the quantum non-demolition measurement of the energy of one oscillator by monitoring the frequency of the second oscillator. Despite the fundamental tradeoff between the coupling strength $g$ and maximum photon storage capacity of the oscillators, it is possible to achieve high fidelity detection of up to 10 photons over time scale of the order of microseconds. We discuss the possibility of observing quantum jumps in the number of photons and related applications.Comment: 5 pages, 3 figure

Yuan Real Exchange Rate Undervaluation, 1997-2006. How Much, How Often? Not Much, Not Often

Yuan real effective exchange rate misalignment is esitimated in a behavioral equilibrium exchange rate (BEER) model for the period 1997 to third quarter 2007. Using the Beveridge-Nelson decomposition a vector error correction model (VECM) of the exchange rate as a function of macroeconomic fundamentals, including government expenditures, economic openness, the balance of trade surplus, and net foreign assets, is estimated. We find that the Chinese Yuan has been fluctuating moderately around its long run equilibrium value with undervaluation up to 4% and overvaluation up to 6% at various points in time since 1997. This result is consistent with findings of many of the most recent studies employing alternative econometric methodologies to determine the equilibrium exchange rate. While the Yuan real effective exchange rate has deviated from equilibrium, and it is sticky, taking over five years to correct 50% of the short run misalignment, it does not appear to have been consistently undervalued as has been widely argued.http://deepblue.lib.umich.edu/bitstream/2027.42/64348/1/wp934.pd

Leaf-excluded percolation in two and three dimensions

We introduce the \emph{leaf-excluded} percolation model, which corresponds to independent bond percolation conditioned on the absence of leaves (vertices of degree one). We study the leaf-excluded model on the square and simple-cubic lattices via Monte Carlo simulation, using a worm-like algorithm. By studying wrapping probabilities, we precisely estimate the critical thresholds to be $0.355\,247\,5(8)$ (square) and $0.185\,022(3)$ (simple-cubic). Our estimates for the thermal and magnetic exponents are consistent with those for percolation, implying that the phase transition of the leaf-excluded model belongs to the standard percolation universality class.Comment: 5 pages, 7 figure

Entanglement production due to quench dynamics of an anisotropic XY chain in a transverse field

We compute concurrence and negativity as measures of two-site entanglement generated by a power-law quench (characterized by a rate 1/tau and an exponent alpha) which takes an anisotropic XY chain in a transverse field through a quantum critical point (QCP). We show that only the even-neighbor pairs of sites get entangled in such a process. Moreover, there is a critical rate of quench, 1/tau_c, above which no two-site entanglement is generated; the entire entanglement is multipartite. The ratio of the two-site entanglements between consecutive even neighbors can be tuned by changing the quench rate. We also show that for large tau, the concurrence (negativity) scales as sqrt{alpha/tau} (alpha/tau), and we relate this scaling behavior to defect production by the quench through a QCP.Comment: 5 pages including 4 figures; added a figure on multipartite entanglement and some references -- this is the published versio