Finite time decoherence could be suppressed efficiently in photonic crystal

The decoherence of two initially entangled qubits in anisotropic band gap photonic crystal has been studied analytically without Born or Markovian approximation. It is shown that the decoherence dynamics of two qubits in photonic crystal is greatly different from that of two qubits in vacuum or subjected to usual non-Markovian reservoir. The results also show that the finite time decoherence invoked by spontaneous emission could be suppressed efficiently and the entanglement of the Bell state possesses odd parity is more easily preserved in photonic crystal than that of the Bell state possesses even parity under the same condition. A store scheme for entangled particle pair is proposed.Comment: 4 pages, 7 figure

Revisiting the new-physics interpretation of the b→cτνb\to c\tau\nu data

We revisit the status of the new-physics interpretations of the anomalies in semileptonic $B$ decays in light of the new data reported by Belle on the lepton-universality ratios $R_{D^{(*)}}$ using the semileptonic tag and on the longitudinal polarization of the $D^*$ in $B\to D^*\tau\nu$, $F_L^{D^*}$. The preferred solutions involve new left-handed currents or tensor contributions. Interpretations with pure right-handed currents are disfavored by the LHC data, while pure scalar models are disfavored by the upper limits derived either from the LHC or from the $B_c$ lifetime. The observable $F_L^{D^*}$ also gives an important constraint leading to the exclusion of large regions of parameter space. Finally, we investigate the sensitivity of different observables to the various scenarios and conclude that a measurement of the tau polarization in the decay mode $B\to D\tau\nu$ would effectively discriminate among them.Comment: matches publised versio