Search

We propose and demonstrate a new approach for realizing spin-orbit coupling with ultracold atoms. We use orbital levels in a double-well potential as pseudospin states. Two-photon Raman transitions between left and right wells induce spin-orbit coupling. This scheme does not require near resonant light, features adjustable interactions by shaping the double-well potential, and does not depend on special properties of the atoms. A pseudospinor Bose-Einstein condensate spontaneously acquires an antiferromagnetic pseudospin texture, which breaks the lattice symmetry similar to a supersolid., National Science Foundation (U.S.) (1506369), United States. Army Research Office (W911NF-14-1-0003), United States. Air Force Office of Scientific Research (FA9550-14-1-0035)

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Physics, 2016., Cataloged from PDF version of thesis., Includes bibliographical references (pages 173-176)., Quantum simulation is emerging as an exciting and active frontier in atomic physics. It allows us not only to verify existing models with high precision, but also to engineer novel systems with strong correlations and exotic topologies. Recent efforts have been made to include synthetic gauge fields and spin-orbit couplings into ultracold quantum gas experiments, which would enable us to study the quantum Hall effect, topological insulators as well as topological superfluids. This thesis will describe the experimental implementation of a new spin-orbit coupled system using pseudospin-1/2 in an optical superlattices, as well as progress towards detecting the stripe phase in this system. The first part of this thesis describes the development of a new apparatus for performing quantum simulations with sodium and lithium in optical lattices. A quantum simulation program is challenging itself, therefore having a stable platform for preparing quantum gases is essential for this task. We'll describe our development in reliable and efficient production of sodium Bose-Einstein condensates and lithium degenerate Fermi gases, as well as the characterization of our optical lattice system in a superfluid to a Mott-insulator quantum phase transition. The dynamics of a Bloch oscillation in a tilted lattice has also been studied as an important step towards the implementation of synthetic magnetic fields in our system. The second part of this thesis describes the experimental realization of spin-orbit coupling in a pseudospin-1/2 system using an optical superlattice. This new scheme uses orbital states in a tilted double-well as the pseudospins, therefore does not require near-resonant Raman light to flip the spins and promise longer lifetimes compared to earlier spin-orbit coupling experiments in atomic gases. It also features a robust miscible ground state with stationary density stripes, which is closely related to the concept of supersolidity in condensed matter systems. We'll, by Wujie Huang., Ph. D.

A degenerate Fermi gas is rapidly quenched into the regime of strong effective repulsion near a Feshbach resonance. The spin fluctuations are monitored using speckle imaging and, contrary to several theoretical predictions, the samples remain in the paramagnetic phase for an arbitrarily large scattering length. Over a wide range of interaction strengths a rapid decay into bound pairs is observed over times on the order of 10ℏ/E[subscript F], preventing the study of equilibrium phases of strongly repulsive fermions. Our work suggests that a Fermi gas with strong short-range repulsive interactions does not undergo a ferromagnetic phase transition., National Science Foundation (U.S.), United States. Office of Naval Research, United States. Air Force Office of Scientific Research. Multidisciplinary University Research Initiative, United States. Army Research Office (grant no. W91NF-07-1-0493), United States. Defense Advanced Research Projects Agency. Optical Lattice Emulator Program

Spin fluctuations and density fluctuations are studied for a two-component gas of strongly interacting fermions along the Bose-Einstein condensate-BCS crossover. This is done by in situ imaging of dispersive speckle patterns. Compressibility and magnetic susceptibility are determined from the measured fluctuations. This new sensitive method easily resolves a tenfold suppression of spin fluctuations below shot noise due to pairing, and can be applied to novel magnetic phases in optical lattices., National Science Foundation (U.S.), United States. Air Force Office of Scientific Research. Multidisciplinary University Research Initiative, United States. Office of Naval Research, United States. Army Research Office (Grant No. W911NF-07-1-0493), United States. Defense Advanced Research Projects Agency. Optical Lattice Emulator Program

We study density profiles of an ideal Fermi gas and observe Pauli suppression of density fluctuations (atom shot noise) for cold clouds deep in the quantum degenerate regime. Strong suppression is observed for probe volumes containing more than 10 000 atoms. Measuring the level of suppression provides sensitive thermometry at low temperatures. After this method of sensitive noise measurements has been validated with an ideal Fermi gas, it can now be applied to characterize phase transitions in strongly correlated many-body systems., United States. Air Force Office of Scientific Research (MURI), United States. Army Research Office (Grant No. W911NF-07-1-0493)