Summary form only given. Our new Rb BEC apparatus features a magnetic transport scheme, good optical access and maximum flexibility. This allows for new experiments which investigate the interaction of a BEC in various environments. Our first experiments will study BEC in a 1D optical lattice. We construct and characterize a coherent accelerator for a condensate which consists of a far detuned standing light wave. We load the BEC adiabatically into the lattice ground state and accelerate the lattice by frequency chirping the lattice laser beams. In simple words the accelerated lattice drags the condensate with it. Coherent acceleration to velocities corresponding to 10 photon recoils has been demonstrated recently in a similar setup. We test whether this scheme can be extended to transport BEC over distances of tens of centimeters. In order to represent a valuable new tool the accelerator has to be able to coherently transfer about 1000 photon recoils (recoil velocity of /sup 87/Rb = 5.85 mm/s) to the atoms in less than 100 ms. We test the efficiency of the transport and study atomic loss, heating and phase corrugation of the condensate wavefunction. In the near future we will extend our work to 3D optical lattices where we will use a Mott insulator state to study molecule formation out of atom number states.
Summary form only given. Our new Rb BEC apparatus features a magnetic transport scheme, good optical access and maximum flexibility. This allows for new experiments which investigate the interaction of a BEC in various environments. Our first experiments will study BEC in a 1D optical lattice. We construct and characterize a coherent accelerator for a condensate which consists of a far detuned standing light wave. We load the BEC adiabatically into the lattice ground state and accelerate the lattice by frequency chirping the lattice laser beams. In simple words the accelerated lattice drags the condensate with it. Coherent acceleration to velocities corresponding to 10 photon recoils has been demonstrated recently in a similar setup. We test whether this scheme can be extended to transport BEC over distances of tens of centimeters. In order to represent a valuable new tool the accelerator has to be able to coherently transfer about 1000 photon recoils (recoil velocity of /sup 87/Rb = 5.85 mm/s) to the atoms in less than 100 ms. We test the efficiency of the transport and study atomic loss, heating and phase corrugation of the condensate wavefunction. In the near future we will extend our work to 3D optical lattices where we will use a Mott insulator state to study molecule formation out of atom number states.
Since the experimental achievement of Bose-Einstein condensation (BEC) in dilute gases, ultra-cold atom systems have proven to be an unparalleled test bed for condensed matter phenomena. With this in mind, our laboratory set out to build an apparatus for the study of the effects of disorder on condensed matter phase transitions using a BEC loaded into one, two, and three-dimensional lattices. My thesis is divided into two main sections. In the first section I describe in detail the design and construction of our apparatus. Our system is designed to form <super>87<\super>Rb condensates of approximately 10<super>5<\super> atoms. We have three possible experimental science chambers. 1. One can perform 1D lattice experiments in the chamber where the condensate is formed. There is a mirror located in vacuum, which is suitable for this purpose. 2. In a glass chamber one can do 1D, 2D, or 3D lattice experiments. Atoms are loaded into a dipole trap (optical tweezer) prior to condensation and transported approximately 20 cm to the glass cell where optical evaporation is performed to form a BEC. 3. One can transfer, using the same techniques as (2), to a chamber with a multi-channel plate detector for Rydberg atom experiments. The experimental results described in my thesis pertain to situation (1). However, I describe some details of (2) in the construction section. The first experiment presented in my thesis demonstrates the effect of disorder on the time-dependent dynamics of lattice systems. We observe that a small perturbation produces a dramatic change in the adiabaticity criteria for loading a BEC into one-dimensional optical lattice. I conclude with experiments that we expect to perform on this apparatus.
We have performed a number of experiments with a Bose-Einstein condensate (BEC) in a one-dimensional optical lattice. Making use of the small momentum spread of a BEC and standard atom optics techniques, a high level of coherent control over an artificial solid-state system is demonstrated. We are able to load the BEC into the lattice ground state with a very high efficiency by adiabatically turning on the optical lattice. We coherently transfer population between lattice states and observe their evolution. Methods are developed and used to perform band spectroscopy. We use these techniques to build a BEC accelerator and a novel, coherent, large-momentum-transfer beam-splitter.
We study the horizontal transport of ultracold atoms over macroscopic distances of up to 20 cm with a moving 1D optical lattice. By using an optical Bessel beam to form the optical lattice, we can achieve nearly homogeneous trapping conditions over the full transport length, which is crucial in order to hold the atoms against gravity for such a wide range. Fast transport velocities of up to 6 m s −1 (corresponding to about 1100 photon recoils) and accelerations of up to 2600 m s −2 are reached. Even at high velocities the momentum of the atoms is precisely defined with an uncertainty of less than one photon recoil. This allows for construction of an atom catapult with high kinetic energy resolution, which might have applications in novel collision experiments.
I have been one of the main responsible for building a new laboratory for Bose-Einstein condensation with 87Rb. In particular, the experimental setup has been designed for performing experiments with Bose-Einstein condensates load into optical lattices of variable geometries. All parts essential for Bose-Einstein condensation are in place. Atoms are collected in a magneto-optical trap, transferred to another vacuum chamber, with better vacuum, and trapped in another magneto-optical trap. Atoms are successfully transferred to a dark magnetic trap, and system for diagnostics with absorption imaging has been realized. We have not yet been able to form a Bose-Einstein condensate, due to a range of technical difficulties. Equipment for alignment of optical lattices with flexible geometry has been designed, built, and tested. This tool has been proven to work as desired, and there is a great potential for a range of unique experiments with Bose-Einstein condensates in optical lattices of various geometries, including superlattices and quasi-periodic lattices. Numerical studies have been made on anisotropic optical lattices, and the existence of a transition between a 2D superfluid phase and a 1D Mott-insulating phase has been confirmed. We have shown that the transition is of Berezinskii-Kosterlitz-Thouless type. In another numerical study it has been shown that using stimulated Raman transitions is a practical method for transferring atoms between states in a double optical lattice. Thus, it will be possible to transfer populations between the lattices, with further applications in qubit read/write operations.
87Rb Bose Einstein Condensate in 3D optical lattice was studied in the regime of weak interaction(the superfluid phase) and strong interaction(the Mott insulating phase). The stability of superfluid currents was studied using a moving optical lattice. The critical momentum for stable superfluid current varies from 0.5 recoil momentum (shallow lattice) to 0 (the Mott insulator) as the system reaches the Mott insulator transition. The phase diagram for the disappearance of superfluidity was studied as a function of momentum and lattice depth. Our phase diagram boundary ex-trapolates to the critical lattice depth for the superfluid-to-MI transition. When a one-dimensional gas was loaded into a moving optical lattice a sudden broadening of the transition between stable and unstable phases was observed. A new auxiliary vacuum chamber, which is called the science chamber, was de-signed and installed to improve optical lattice experimental performance and imaging resolution power. Atoms are transported from the main chamber to the science cham-ber. By further evaporation cooling, BECs with N- 2-3 x 104 atoms are produced
A Bose-Einstein condensate (BEC) is a macroscopic ensemble of atoms that collectively behaves as a single quantum-mechanical object. In this thesis I describe an apparatus built to create and study a BEC, as well as initial experiments carried out using a one-dimensional optical standing wave (optical lattice) to manipulate the BEC. In the first experiment, a weak optical lattice Bragg-reflects a BEC moving in a nearly harmonic trap. The Bragg reflection combined with the harmonic trapping potential cause the BEC to oscillate, much as light oscillates in an optical cavity. In the second experiment, a deep optical lattice applied to an atom cloud for a short duration is used to split and recombine the atomic wavefunction. By doing this we can create two different types of atom interferometer: a small-separation atom interferometer which works with either a BEC or a thermal gas, and a large-separation atom interferometer which works only with a BEC and whose interferometric arms are, in principle, separately addressable. In the third experiment, an optical lattice potential is slowly turned on. Under the influence of this lattice potential, the BEC loses its superfluid properties, but fully regains them when the lattice is turned back off. This behavior is consistent both with a reversible transition to a 1-D Mott insulator state and with mean-field effects in a deep lattice; both interpretations are discussed. In the latter part of this thesis I describe an apparatus designed to accommodate experiments involving both a BEC and an ion. The interactions between an ion and a BEC have never before been experimentally investigated. Our apparatus includes both the means to localize an ion by actively shielding against stray electric fields and to spatially image ions. This should allow future experiments in which a single ion is embedded in a BEC. In addition to imaging ions, the apparatus provides the capability to create high-resolution images of distributions of neutral atoms by photoionizing them and then quickly imaging them. I conclude the thesis with a discussion of future experiments exploring ion-BEC interactions.