Effect of phase noise on quantum correlations in Bose-Josephson junctions

Abstract

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.

Mesoscopic quantum superpositions in bimodal Bose-Einstein condensates: Decoherence and strategies to counteract it

“…Equation (7) agrees with Eq. (19) in Ref. [19] up to a global phase factor but it disagrees with Ref.…”

“…(8), supplemented by a dephasing environment. This kind of model was already used in the context of spin squeezing [19,64] in particular to predict the optimum spin squeezing at finite temperature [64]. Contrarily to Refs.…”

“…Hamiltonian [19] and by including the effect of the additional N -dependent drift termhχNŜ z in the Hamiltonian, we obtain at the cat-state time:…”

“…The stationary condensate wave functions φ and the Gross-Pitaevskii energy E GP have been computed numerically for different pairs (N a , N b ) (in practice a few thousands) to construct the Hamiltonian (22). In order to find the optimal conditions, we were scanning the experimental parameters space, each time performing the evolution starting from the initial condition (19), optimizing entanglement witnesses that are sensitive to the presence of a Schrödinger cat. To avoid extreme parameters that would make the experimental realization more difficult, we have restricted the search to trapping frequencies ratios smaller than 20.…”

Parameter estimation in memory-assisted noisy quantum interferometry

“…Basing on recent experimental results [12,13], we assumed that the two-body interactions, which are essential for the state preparation [4,7,17], are absent during the phase imprint. In the next step, one should specify the Hamiltonian of the environmentĤ E , and determine how it interacts with the system viaĤ int .…”