Effects of depolarizing quantum channels on BB84 and SARG04 quantum cryptography protocols

We report experimental studies on the effect of the depolarizing quantum channel on weak-pulse BB84 and SARG04 quantum cryptography. The experimental results show that, in real world conditions in which channel depolarization cannot be ignored, BB84 should perform better than SARG04.Comment: 4 pages, 4 figure

Purchasing Power Parity and Country Characteristics: Evidence from Time Series Analysis

This paper investigates the relationships between country characteristics and the validity of PPP. We use three alternative time series methods to test for the stationarity of real exchange rates for each of the 72 countries over the period from 1976 to 2005. Our result shows that the evidence of PPP exhibits geographic difference. It is most likely to find stationary real exchange rates for European countries, whereas it is least likely to obtain the result of supporting PPP for Asian countries. We then use a probit regression model to examine if county characteristics are related to the validity of PPP. The probit regression result reveals that the validity of PPP decreases with inflation rate and increases with nominal exchange rate volatility.Purchasing power parity, Country characteristics, Unit root tests

Analysis of DNA-binding Proteins in Yeast Saccharomyces Cerevisiae

Gene expression is an elaborate and finely tuned process involving the regulated interactions of multiple proteins with promoter and enhancer elements. A variety of approaches are currently used to study these interactions in vivo, in vitro as well as in silico. With the genome sequences of many organisms now readily available, a plethora of DNA functional elements have been predicted, but the process of identifying the proteins that bind to them in vivo remains a bottleneck. I developed two high-throughput assays to address this issue. The first is a modification of the yeast one-hybrid assay. The second is probing protein microarrays with DNA sequence elements. Using these methods, I identified two proteins, Sef1 and Yjl103c, that bind to the same DNA sequence element. Sef1 and Yjl103c are little-characterized members of the zinc cluster family of transcription factors of S. cerevisiae. Characterization of their mechanism of action as well as identification of some of their target genes leads to the conclusion that they play a pivotal role in the transcriptional regulation of utilization of nonfermentable carbon sources by budding yeast

Enhancing quantum entanglement for continuous variables by a coherent superposition of photon subtraction and addition

We investigate how the entanglement properties of a two-mode state can be improved by performing a coherent superposition operation of photon subtraction and addition, proposed by Lee and Nha [Phys. Rev. A 82, 053812 (2010)], on each mode. We show that the degree of entanglement, the EPR-type correlation, and the performance of quantum teleportation can be all enhanced for the output state when the coherent operation is applied to a two-mode squeezed state. The effects of the coherent operation are more prominent than those of the mere photon subtraction and the addition particularly in the small squeezing regime, whereas the optimal operation becomes the photon subtraction in the large-squeezing regime.Comment: 6 pages, 6 figures, published versio

Experimental verification of the commutation relation for Pauli spin operators using single-photon quantum interference

We report experimental verification of the commutation relation for Pauli spin operators using quantum interference of the single-photon polarization state. By superposing the quantum operations $\sigma_z \sigma_x$ and $\sigma_x \sigma_z$ on a single-photon polarization state, we have experimentally implemented the commutator, $[\sigma_{z}, \sigma_{x}]$, and the anticommutator, $\{\sigma_{z}, \sigma_{x}\}$, and have demonstrated the relative phase factor of $\pi$ between $\sigma_z \sigma_x$ and $\sigma_x \sigma_z$ operations. The experimental quantum operation corresponding to the commutator, $[\sigma_{z}, \sigma_{x}]=k\sigma_y$, showed process fidelity of 0.94 compared to the ideal $\sigma_y$ operation and $|k|$ is determined to be $2.12\pm0.18$.Comment: 4pages, 3 figure

Reversing the Weak Quantum Measurement for a Photonic Qubit

We demonstrate the conditional reversal of a weak (partial-collapse) quantum measurement on a photonic qubit. The weak quantum measurement causes a nonunitary transformation of a qubit which is subsequently reversed to the original state after a successful reversing operation. Both the weak measurement and the reversal operation are implemented linear optically. The state recovery fidelity, determined by quantum process tomography, is shown to be over 94% for partial-collapse strength up to 0.9. We also experimentally study information gain due to the weak measurement and discuss the role of the reversing operation as an information erasure

The Extremely High-Velocity Outflow from the Luminous Young Stellar Object G5.89-0.39

We have imaged the extremely high-velocity outflowing gas in CO (2-1) and (3-2) associated with the shell-like ultracompact HII region G5.89-0.39 at a resolution of ~3" (corresponding to ~4000 AU) with the Submillimeter Array. The integrated high-velocity (>45 km/s) CO emission reveals at least three blueshifted lobes and two redshifted lobes. These lobes belong to two outflows, one oriented N-S, the other NW-SE. The NW-SE outflow is likely identical to the previously detected Br_gamma outflow. Furthermore, these outflow lobes all clearly show a Hubble-like kinematic structure. For the first time, we estimate the temperature of the outflowing gas as a function of velocity with the large velocity gradient calculations. Our results reveal a clear increasing trend of temperature with gas velocity. The observational features of the extremely high-velocity gas associated with G5.89-0.39 qualitatively favor the jet-driven bow shock model.Comment: 14 pages, 4 figures, accepted for publication in ApJ Letter