[show abstract][hide abstract] ABSTRACT: Coherence properties of Bose-Einstein condensates offer the potential for improved interferometric phase contrast. However, decoherence effects due to the mean-field interaction shorten the coherence time, thus limiting potential sensitivity. In this work, we demonstrate increased coherence times with number squeezed states in an optical lattice using the decay of Bloch oscillations to probe the coherence time. We extend coherence times by a factor of 2 over those expected with coherent state Bose-Einstein condensate interferometry. We observe quantitative agreement with theory both for the degree of initial number squeezing as well as for prolonged coherence times.
[show abstract][hide abstract] ABSTRACT: We study the response of BEC+optical lattice system to sudden frustration of Josephson tunneling between adjacent lattice sites in the large filling factor (soft) regime. We introduce a new experimental method which effectively discriminates between homogeneous (on-site) phase diffusion and inhomogeneous (site-to-site) dephasing mechanisms. With this method, we observe quantitative agreement between the predicted and measured phase diffusion times. In particular, we demonstrate that the phase diffusion time can be increased by reducing the number fluctuations associated with the initial lattice states. This work extends the work of Greiner, et al. to the large filling factor regime. Finally, we describe and demonstrate a technique for retrieval of long range phase coherence from this system. Surprisingly, coherence can be suddenly regained by abruptly allowing Josephson tunneling. We discuss the implications of these observations for envisioned superfluid de Broglie wave interferometers and in the study of non-adiabatic effects in superfluid/Mott-insulating systems.  Orzel, C., Tuchman, A. K., Fenselau, M. L., Yasuda, M. & Kasevich, M. A. Science 291, 2386-2389 (2001).  A. Imamoglu, M. Lewenstein & L. You. Phys. Rev. Lett. 78, 2511(1997).  M. Greiner, O. Mandel, T. Esslinger, T. W. H"ansch & I. Bloch. Nature 415, 39 (2002)