Spin squeezing: transforming one-axis-twisting into two-axis-twisting

Squeezed spin states possess unique quantum correlation or entanglement that are of significant promises for advancing quantum information processing and quantum metrology. In recent back to back publications [C. Gross \textit{et al, Nature} \textbf{464}, 1165 (2010) and Max F. Riedel \textit{et al, Nature} \textbf{464}, 1170 (2010)], reduced spin fluctuations are observed leading to spin squeezing at -8.2dB and -2.5dB respectively in two-component atomic condensates exhibiting one-axis-twisting interactions (OAT). The noise reduction limit for the OAT interaction scales as $\propto 1/{N^{2/3}}$, which for a condensate with $N\sim 10^3$ atoms, is about 100 times below standard quantum limit. We present a scheme using repeated Rabi pulses capable of transforming the OAT spin squeezing into the two-axis-twisting type, leading to Heisenberg limited noise reduction $\propto 1/N$, or an extra 10-fold improvement for $N\sim 10^3$.Comment: 4 pages, 3 figure

Semi-Inclusive B\to K(K^*) X Decays with Initial Bound State Effects

The effects of initial $b$ quark bound state for the semi-inclusive decays $B\to K(K^*) X$ are studied using light cone expansion and heavy quark effective theory methods. We find that the initial bound state effects on the branching ratios and CP asymmetries are small. In the light cone expansion approach, the CP-averaged branching ratios are increased by about 2% with respect to the free $b$-quark decay. For $\bar B^0 \to K^- (K^{*-}) X$, the CP-averaged branching ratios are sensitive to the phase $\gamma$ and the CP asymmetry can be as large as 7% (14%), whereas for $B^-\to \bar K^0 (\bar K^{*0})X$ the CP-averaged branching ratios are not sensitive to $\gamma$ and the CP asymmetries are small ($< 1$). The CP-averaged branching ratios are predicted to be in the ranges $(0.53 \sim 1.5)\times 10^{-4}$ [$(0.25 \sim 2.0)\times 10^{-4}$] for $\bar B^0 \to K^- (K^{*-})X$ and $(0.77 \sim 0.84)\times 10^{-4}$ [$(0.67 \sim 0.74)\times 10^{-4}$] for $B^-\to \bar K^0 (\bar K^{*0}) X$, depending on the value of the CP violating phase $\gamma$. In the heavy quark effective theory approach, we find that the branching ratios are decreased by about 10% and the CP asymmetries are not affected. These predictions can be tested in the near future.Comment: 29 pages, 12 ps figure