Decoherence and entanglement in a bosonic Josephson junction: Bose-enhanced quantum-Zeno control of phase-diffusion

摘要

We study the effect of decoherence on dynamical phase diffusion in thetwo-site Bose-Hubbard model. Starting with an odd parity excited coherentstate, the initial loss of single particle coherence varies from small boundoscillations in the Rabi regime, through hyperbolic depletion in the Josephsonregime, to a Gaussian decay in the Fock regime. The inclusion of local-sitenoise, measuring the relative number difference between the modes, is shown toenhance phase-diffusion. In comparison, site-indiscriminate noise measuring thepopulation imbalance between the two quasi-momentum modes, slows down the lossof single-particle coherence. Decoherence thus either enhances or suppressesphase-diffusion, depending on the details of system-bath coupling and theoverlap of decoherence pointer states with collisional-entanglement pointerstates. The deceleration of phase-diffusion due to the coupling with theenvironment may be viewed as a many-body quantum-Zeno effect. The extendedeffective decay times in the presence of projective measurement, are furtherenhanced with increasing number of particles $N$, by a bosonic factor of$\sqrt{N}$ in the Fock regime and $N/\log{N}$ in the Josephson regime.