Scientific Results

Coherence and entanglement in the ground state of a bosonic Josephson junction: From macroscopic Schrodinger cat states to separable Fock states

Year: 2011

Authors: Mazzarella G., Salasnich L., Parola A., Toigo F.

Autors Affiliation: Dipartimento di Fisica “Galileo Galilei” and Consorzio Nazionale Interuniversitario per la Scienze Fisiche della Materia (CNISM), Università di Padova, Via Marzolo 8, I-35122 Padova, Italy;
Istituto Nazionale di Ottica (INO) del Consiglio Nazionale delle Ricerche (CNR), via G. Sansone 1, I-50019 Sesto Fiorentino, Italy;
Dipartimento di Fisica e Matematica and CNISM,Universit`a dell’Insubria, Via Valleggio 11, I-22100 Como, Italy

Abstract: We consider a bosonic Josephson junction made of N ultracold and dilute atoms confined by a quasi-one-dimensional double-well potential within the two-site Bose-Hubbard model framework. The behavior of the system is investigated at zero temperature by varying the interatomic interaction from the strongly attractive regime to the repulsive one. We show that the ground state exhibits a crossover from a macroscopic Schrodinger-cat state to a separable Fock state through an atomic coherent regime. By diagonalizing the Bose-Hubbard Hamiltonian we characterize the emergence of the macroscopic cat states by calculating the Fisher information F, the coherence by means of the visibility a of the interference fringes in the momentum distribution, and the quantum correlations by using the entanglement entropy S. Both Fisher information and visibility are shown to be related to the ground-state energy by employing the Hellmann-Feynman theorem. This result, together with a perturbative calculation of the ground-state energy, allows simple analytical formulas for F and a to be obtained over a range of interactions, in excellent agreement with the exact diagonalization of the Bose-Hubbard Hamiltonian. In the attractive regime the entanglement entropy attains values very close to its upper limit for a specific interaction strength lying in the region where coherence is lost and self-trapping sets in.

Journal/Review: PHYSICAL REVIEW A

Volume: 83 (5)      Pages from: 053607  to: 053607

KeyWords: BEC
DOI: 10.1103/PhysRevA.83.053607

Citations: 39
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English