Bulletin of the American Physical Society
38th Annual Meeting of the Division of Atomic, Molecular, and Optical Physics
Volume 52, Number 7
Tuesday–Saturday, June 5–9, 2007; Calgary, Alberta, Canada
Session C2: Focus Session: Matter Wave Interferometry |
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Chair: E. Demler, Harvard University Room: TELUS Convention Centre Macleod D |
Wednesday, June 6, 2007 1:30PM - 2:06PM |
C2.00001: Interference and Coherence in 1-d Bose-Einstein-Condensates Invited Speaker: Employing RF induced adiabatic potentials [1] on AtomChips [2] enables coherent manipulation of trapped matter waves with high precision. Using our exceptionally smooth AtomChip potentials [3] we study 1d condensates at strong transversal confinement ($>$10kHz) and extreme aspect ratio up to 10000, which can be coherently split along their long axis [4]. Bringing the two split clouds together we observe interference between the two ensembles. The interference pattern itself is sensitive probe of the order parameter in the 1d quantum gas and allows detailed studies of its coherence properties: \begin{itemize} \item It allows precise separation between 'condensed' and 'thermal' component \item Adjusting the barrier between the separated ensembles we can study tunnel coupling and phase locking between two 1d condensates and employ phase noise thermometry to measure the local temperature. \item Coherently splitting into two isolated systems with an initially fixed phase relation, we investigate the dynamics of the phase fluctuations of a 1d quantum gas, and their influence on the statistics of the interferences. \item The evolution of the interference of coherently split quantum gas can be compared to completely separated, independently created 1d condensates. \end{itemize} Furthermore the RF coupling allows many \textit{different} potential shapes to be realized, including a 2d cylinder shaped trap. The later allows to create a 2d condensate with periodic boundary conditions which exhibits peculiar interference. In addition combining the AtomChip with a 1d optical lattice of 2d planes we observe coherent Blochoszillations close to the AtomChip surface [5], which gives us a new tool for coherent manipulation of 2d mesoscopic quantum gases. \newline \newline [1] I. Lesanovsky \textit{et al.}, Phys. Rev. A \textbf{73}, 033619 (2006); Phys. Rev. A \textbf{74}, 033619(2006). \newline [2] R. Folman, \textit{et al. }, Adv. At. Mol. Opt. Phys. \textbf{48,} 263 (2002). \newline [3] S. Groth \textit{et al.}, Appl. Phys. Lett. \textbf{85}, 2980 (2004). P. Kruger,. \textit{et al.}, cond-mat/0504686 (2005). \newline [4] T. Schumm \textit{et al.}, Nature Physics \textbf{1}, 57 (2005); S. Hofferberth et al. Nature Physics \textbf{2}, 710 (2006). \newline [5] D. Gallego, Diplomarbeit Univ. Heidelberg (2005). [Preview Abstract] |
Wednesday, June 6, 2007 2:06PM - 2:18PM |
C2.00002: On-chip Bose-Einstein condensate interferometer with 0.5 mm arm length Stephen R. Segal, Quentin Diot, Eric A. Cornell, Mara Prentiss, Alex A. Zozulya, Dana Z. Anderson We demonstrate a chip-based Michelson interferometer for Bose-Einstein condensates in which a harmonic trap reflects the atoms. The condensate is split by diffraction from momentary exposure to an off-resonant standing light field. The two clouds propagate in opposite directions along a waveguide having a weak (6 Hz) harmonic axial confinement. The condensates reflect from the axial potential at classical turning points separated by about 0.5 mm. Upon returning to the trap center, the two clouds are recombined by a second exposure to the standing light field. The resulting three clouds are allowed to remain in the guide for a brief time. The atoms are then released from the guide and imaged after 15 ms of ballistic expansion. The total propagation time can be set to 80 or 160 ms. We use principal component analysis of a series of many images to study the coherence of the recombined atoms. [Preview Abstract] |
Wednesday, June 6, 2007 2:18PM - 2:30PM |
C2.00003: Phase Sensitive Recombination of two Bose-Einstein Condensates on an Atom Chip G.-B. Jo, J.-H. Choi, C. Christensen, Y.R. Lee, T.A. Pasquini, W. Ketterle, D.E. Pritchard We report on the relative phase sensitive recombination of two split Bose-Einstein condensates on an atom chip. By merging two separate condensates with well-defined relative phase and by measuring the atom loss due to the recombination, we read out the relative phase of two phase coherent condensates. The strong dependence of the atom loss of the merged condensate on the relative phase is attributed to development of a dark soliton which increases the temperature of the merged condensate through the dissipation. In addition, we study the dependence of the atom loss on the time scale of the merge. [Preview Abstract] |
Wednesday, June 6, 2007 2:30PM - 2:42PM |
C2.00004: Matter wave interferometry with phase fluctuating condensates J.-H. Choi, G.-B. Jo, T.A. Pasquini, C.A. Christensen, Y.R. Lee, W. Ketterle, D.E. Pritchard We report on the thermal phase fluctuations in condensates trapped on atom chips and address the question of robustness of chip-based BEC interferometry against phase fluctuations. Since quasi-1D condensates created on atom chips are typically in the phase fluctuating regime with a phase coherence length shorter than the spatial extent of the cloud, the presence of the fluctuation may degrade interference fringes and, consequently, erase the relative phase information in the fringes. In the experiment, we produce a double-well potential in the plane parallel to {\bf g} by deforming a single well using adiabatic rf-induced splitting. We observe a decrease in the fringe contrast as the temperature increases, indicating that fringes become wavier at higher temperature. We also discuss the effect of fluctuations on the phase coherence of the split condensates. [Preview Abstract] |
Wednesday, June 6, 2007 2:42PM - 3:18PM |
C2.00005: Two Weakly-Coupled Condensates Invited Speaker: The recent realization of a single weak link for an atomic Bose-Einstein condensate in an optical double-well potential allows for the first time observation of coherent Josephson oscillations directly on the level of populations on either side of the junction. Furthermore it opens up the way to fully characterize the tunneling dynamics since not only the dynamics of the population difference can be measured but even the time evolution of the relative phase is detectable. How the residual interaction of the atoms can lead to a new dynamical regime, which is characterized by an inhibition of tunneling, will be discussed in detail. The well controlled experimental setup of the atomic system allows for a quantitative study of thermally induced fluctuations of the relative phase between the weakly linked condensates. The experimentally observed fluctuations are in quantitative agreement with the theoretical predictions and give insight into the coherence of two weakly coupled condensates. Since the thermal fluctuations exist for any non-zero temperature their measurement can be employed as a new type of primary thermometer for atomic Bose-Einstein condensates working in a regime were standard methods such as time of flight fail. Our recent results on the heat capacity of a quantum gas at ultra low temperatures using this new noise-thermometer will be presented. [Preview Abstract] |
Wednesday, June 6, 2007 3:18PM - 3:30PM |
C2.00006: An experiment to measure the electric polarizability of $^{87}$Rb using a condensate interferometer Benjamin Deissler, K. Jeramy Hughes, John H.T. Burke, Cass Sackett Atom interferometry using Bose-Einstein condensates has developed to a point at which intersting measurements are now feasible. We have demonstrated a condensate interferometer with coherence time over 70 ms and arm separations over $200 \mu$m. This allows each packet to be individually accessible. We plan to use this device to measure the electric polarizability of $^{87}$Rb by applying a precise electric field to one packet and not the other. By observing the resulting phase shift, we expect to be able to extract the polarizability with a relative accuracy better than $10^{-3}$. We will report on the experimental developments. [Preview Abstract] |
Wednesday, June 6, 2007 3:30PM - 3:42PM |
C2.00007: Obtaining a high-visibility Bose-Einstein condensate interferometer K. Jeramy Hughes, Benjamin Deissler, John H.T. Burke, Cass Sackett We have previously reported on an atom interferometer based on Bose-Einstein condensates of $^{87}$Rb in a weakly confining magnetic trap [1]. Previous results were limited to interference visibilities of about 1/2 and coherence times of about 45ms. We have identified several effects that limited these figures, including motional excitation of the condensate, spatial noise in the coupling laser beams, and noise in the magnetic trap currents. Resulting improvements to the apparatus have increased the interferometer visibility to near unity for short times, and have permitted operation at times over 70ms. We will report on our current performance. \newline \newline [1] Garcia et al., Phys. Rev. A 74, 031601(R) (2006) [Preview Abstract] |
Wednesday, June 6, 2007 3:42PM - 3:54PM |
C2.00008: Theoretical analysis of cold atom interferometers with optical control of dynamics James Stickney, Dana Z. Anderson, Alex Zozulya Atom interferometers using Bose-Einstein condensate that is confined in a waveguide and manipulated by optical pulses have been limited by their short coherence times. We present a theoretical model that offers a physically simple explanation for the loss of contrast for both a single-pass and double-pass interferometers. For the case of a singles-pass device, we propose the method for increasing the fringe contrast by recombining the atoms at a different time. A simple, quantitatively accurate, analytical expression for the optimized recombination time is presented and used to place limits on the physical parameters for which the contrast may be recovered. For the case of a double-pass interferometer, we place an upper limit on the device's coherence time. [Preview Abstract] |
Wednesday, June 6, 2007 3:54PM - 4:06PM |
C2.00009: Gold coated nano gratings for atom optics Vincent Lonij, John Perreault, Oleg Kornilov, Alex Cronin The Van der Waals (VdW) interaction between neutral atoms is important to the dynamics of mechanical systems on nanometer scales. We used diffraction of sodium atoms from nano gratings to measure the Van der Waals potentials for atoms and different surfaces with improved precision. Atoms passing through the grating acquire an additional phase shift due to the attractive potential between the atoms and the grating bars, causing the diffraction pattern to be modified [1]. Previous measurements reported the VdW coefficient for sodium atoms and a silicon-nitride(SiNx) surface [2]. In our experiment we used a SiNx grating coated with a 2 nm layer of gold and we were able to measure a 40\% increase in the VdW coefficient due to the gold. We also improved precision by combing results from the sodium diffraction experiment with results from a diffraction experiment with helium atoms on the same gratings. \newline \newline [1] R. E. Grisenti, W. Schollkopf, J. P. Toennies, G. C. Hegerfeldt, and T. Kohler. Phys. Rev. Lett., 83(9):1755, 1999. \newline [2] J. D. Perreault, A. D. Cronin, and T. A. Savas. Phys. Rev. A, 71(5):053612, 2005. [Preview Abstract] |
Wednesday, June 6, 2007 4:06PM - 4:18PM |
C2.00010: Modifying atom-surface vdW interactions with light Alex Cronin, Vincent Lonij, John Perreault Electromagnetic radiation can modify van der Waals interactions. We predict how the atom-surface interaction potentials should depend on light frequency, intensity, and polarization. We also present progress towards observing this effect with an experiment based on atom diffraction from a nanograting that is illuminated by a laser. [Preview Abstract] |
Wednesday, June 6, 2007 4:18PM - 4:30PM |
C2.00011: Electron Interferometry with Nanogratings Ben McMorran, Alex Cronin We present an electron interferometer based on near-field diffraction from two nanostructure gratings. Lau fringes are observed with an imaging detector, and revivals in the fringe visibility occur as the separation between gratings is increased from 0.2 to 2.7 mm. The oscillations in visibility depend predictably on the wavelength of incident electrons. This verifies that 5 keV electrons diffracted by nanostructures remain coherent after propagating farther than the Talbot length, and proves that a Talbot-Lau interferometer for electrons can be built with nanostructure gratings. Distorted fringes due to a phase object are used to demonstrate an application for this new type of electron interferometer. [Preview Abstract] |
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