Effect of phase noise on useful quantum correlations in Bose Josephson   junctions
  In a two-mode Bose Josephson junction the dynamics induced by a sudden quench of the tunnel amplitude leads to the periodic formation of entangled states. For instance, squeezed states are formed at short times and macroscopic superpositions of phase states at later times. The two modes of the junction can be viewed as the two arms of an interferometer; use of entangled states allows to perform atom interferometry beyond the classical limit. Decoherence due to the presence of noise degrades the quantum correlations between the atoms, thus reducing phase sensitivity of the interferometer. We consider the noise induced by stochastic fluctuations of the energies of the two modes of the junction. We analyze its effect on squeezed states and macroscopic superpositions and study quantitatively the amount of quantum correlations which can be used to enhance the phase sensitivity with respect to the classical limit. To this aim we compute the squeezing parameter and the quantum Fisher information during the quenched dynamics. For moderate noise intensities we show that these useful quantum correlations increase on time scales beyond the squeezing regime. This suggests multicomponent superpositions as interesting candidates for high-precision atom interferometry. 
Giulia Ferrini, Dominique Spehner, Anna Minguzzi and F.W.J. Hekking
quant-ph