Bulletin of the American Physical Society
2005 36th Meeting of the Division of Atomic, Molecular and Optical Physics
Tuesday–Saturday, May 17–21, 2005; Lincoln, Nebraska
Session B1: Matter Optics and Atom Chips |
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Chair: Herman Batelaan, University of Nebraska Room: Burnham Yates Conference Center Ballroom I |
Wednesday, May 18, 2005 10:30AM - 11:06AM |
B1.00001: Quantum Optics of Ultracold Molecular Dimers Invited Speaker: A remarkable outcome of the availability of ultracold, quantum degenerate atomic samples is the coherent formation of molecular dimers by means of Feshbach resonances and by two-photon Raman photoassociation. These processes are formally closely related to the optical three-wave mixing mechanisms of second-harmonic generation and sum-frequency generation, with however the important difference that the atoms and molecules involved can be either bosonic or fermionic. The talk will discuss the dependence of the quantum statistics of the molecular field on the initial state of the atomic source, considering the cases of an atomic Bose condensate, a quantum-degenerate gas of atomic fermions, and a BCS-type superfluid Fermi gas. For short enough times, BEC atomic states are found to give rise to an essentially coherent molecular field, while a normal Fermi gas results in a a molecular field with `chaotic' molecule statistics, analogous to the photon statistics of a classical light source. The BCS situation is intermediate between the two. We also discuss the impact of quantum fluctuations on the early stages of molecule formation by means of the so-called ``passage time statistics'' familiar from studies of superradiance. In collaboration with D. Meiser and H. Uys, University of Arizona, and C. P. Search, Stevens Institute of Technology [Preview Abstract] |
Wednesday, May 18, 2005 11:06AM - 11:42AM |
B1.00002: An Atom Michelson Interferometer on a Chip Invited Speaker: An atom Michelson interferometer is implemented on an ``atom chip.'' The chip uses lithographically patterned conductors and external magnetic fields to produce and guide a Bose-Einstein condensate. Splitting, retroreflecting, and recombining of condensate atoms are achieved within the magnetic waveguide by a standing-wave light field having a wave vector aligned along the guide. Splitting and recombining are achieved with a pair of standing light field pulses each 20 $\mu $s in duration and separated by 63 $\mu $s. This pair of pulses is such that an a single BEC cloud initially at rest is converted into a pair of oppositely directed clouds having momentum $p=\pm 2\hbar k$ with essentially no atoms remaining stationary or in higher diffracted orders. Retroreflection of the two clouds is achieved by a longer (150 $\mu $s) pulse of the standing wave. When the atoms have returned to their starting position, the recombining pulse pair leaves the atoms in three clouds representing two different states: one cloud with zero momentum, $\left| {p=0} \right\rangle $ and a pair of clouds representing the state $\left| {p=\pm 2\hbar k} \right\rangle $. The population of these two states corresponds to the intensity of light from the two output ports of the beamsplitter in an optical Michelson interferometer. A differential phase shift between the two arms of the atom interferometer is introduced either with a magnetic-field gradient or with an initial condensate velocity. The populations of the two states is seen to vary sinusoidally and in anti-phase with the path difference as expected. We find that the interference contrast decays with propagation time in the waveguides: 20{\%} contrast is observed with an atom propagation time of 10 ms. [Preview Abstract] |
Wednesday, May 18, 2005 11:42AM - 12:18PM |
B1.00003: Biprism interferometry with electrons and ions, a valuable tool to study the fundamentals of quantum mechanics and quantum statistics Invited Speaker: Our miniaturized electron biprism interferometer $[1]$ proved to be many orders of magnitude less sensitive to mechanical and electromagnetic disturbances than conventional interferometers (modified electron microscopes). Experiments so far inconceivable with electron waves, e.g., to rotate an electron interferometer on a turntable and to prove the Sagnac phase shift $[2,3]$ or to realize biprism interferences with He-ions $[4]$ with wavelengths as small as 0.3 pm became reality. A crossed-field analyzer (Wien filter) in the beam path of our electron interferometer allows to introduce electric and magnetic Aharonov-Bohm phase differences and transit time differences between the interfering wave packets $[5]$. For wave packet shifts introduced by the Wien filter which exceed the coherence length, which-path information is available in principle, leading to vanishing fringe contrast. Since which-path information is not read out in this experiment, fringe contrast can be restored by compensating the longitudinal shift in a second shifting device. Only recently we succeeded to demonstrate that electrons arrive at two coherently illuminated detectors `antibunched' $[6]$, i.e., according to the demands of Fermi statistics. At present, our intertest is focused on decoherence. Coherently split electron waves propagate over a resistive plate. Which-path information of the electrons decreases with increasing height of flight. In turn the contrast of the fringes increases $[7,8]$.\\ $[1]$ F. Hasselbach, Z. Phys. B -- Condensed Matter {\bf{71}}(1988), 443-449.\\ $[2]$ F. Hasselbach, M. Nicklaus, Phys. Rev. A {\bf{48}}(1993), 143-151.\\ $[3]$ R. Neutze, F. Hasselbach, Phys. Rev. A {\bf{58}}(1998), 557-565.\\ $[4]$ F. Hasselbach, U. Maier, in {\it{Quantum Coherence and Decoherence: Proc. ISQM-Tokyo`98}} p. 299-302, eds. Y.Y. Ono and K. Fujikawa, Amsterdam, Elsevier, 1999.\\ $[5]$ M. Nicklaus, F. Hasselbach, Phys. Rev. A {\bf{48}}(1993), 152-160.\\ $[6]$ Harald Kiesel, Andreas Renz \& F. Hasselbach, Nature {\bf{418}}(2002), 392-394.\\ $[7]$ H.D. Zeh, Found. Phys. {\bf{1}}(1970), 69-76.\\ $[8]$ J.R. Anglin, J.P. Paz, W.H. Zurek, Phys. Rev. A {\bf{55}}(1997), 4041-4053. [Preview Abstract] |
Wednesday, May 18, 2005 12:18PM - 12:54PM |
B1.00004: Novel methods for matter interferometry with nanosized objects Invited Speaker: We discuss the current status and prospects for novel experimental methods for coherence$^{1,2}$ and decoherence$^{3}$ experiments with large molecules. Quantum interferometry with nanosized objects is interesting for the exploration of the quantum-classical transition. The same experimental setup is also promising for metrology applications and molecular nanolithography. Our coherence experiments with macromolecules employ a Talbot-Lau interferometer. We discuss some modifications to this scheme, which are required to extend it to particles with masses in excess of several thousand mass units. In particular, the detection in all previous interference experiments with large clusters and molecules, was based on either laser ionization$^{1}$ (e.g. Fullerenes) or electron impact ionization$^{2}$ (e.g. Porphyrins etc.). However, most ionization schemes run into efficiency limits when the mass and complexity of the target particle increases. Here we present experimental results for an interference detector which is truly scalable, i.e. one which will even improve with increasing particle size and complexity. ``Mechanically magnified fluorescence imaging'' (MMFI), combines the high spatial resolution, which is intrinsic to Talbot Lau interferometry with the high detection efficiency of fluorophores adsorbed onto a substrate. In the Talbot Lau setup a molecular interference pattern is revealed by scanning the 3$^{rd}$ grating across the molecular beam$^{1}$. The number of transmitted molecules is a function of the relative position between the mask and the molecular density pattern. Both the particle interference pattern and the mechanical mask structure may be far smaller than any optical resolution limit. After mechanical magnification by an arbitrary factor, in our case a factor 5000, the interference pattern can still be inspected in fluorescence microscopy. The fluorescent molecules are collected on a surface which is scanned collinearly and synchronously behind the 3rd grating. The resulting image of the interference pattern is by far large enough to be easily seen by the unaided eye. High contrast interference fringes could be recorded with dyes molecules. $^{1}$B. Brezger et al. , Phys. Rev. Lett. \textbf{88}, 100404 (2002). $^{2}$L. Hackerm\"{u}ller et al. Phys. Rev. Lett \textbf{91}, 90408 (2003). $^{3}$L. Hackerm\"{u}ller et al. Nature 427, 711 (2004). [Preview Abstract] |
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