Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Physics, 2012. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 109-111). / We present an experiment exploring electromagnetically induced transparency (EIT) in Rydberg atoms in order to observe optical nonlinearities at the single photon level. ⁸⁷Rb atoms are trapped and cooled using a magneto-optical trap (MOT) and a far off resonance dipole trap (FORT). Once the system is prepared, a ladder EIT scheme with Rydberg atoms is used to map the photon field onto the ensemble. The powerful dipole interaction between Rydberg atoms allows the system to exhibit many-body quantum mechanical effects. We also describe an imaging method to observe the Rydberg blockade. Last of all, we present a preliminary measurement of EIT in a Rydberg system. In this measurement, the transmission shows sensitivity to the applied photon flux, and exhibits temporal correlations in the photons exiting the EIT medium. / by Anton Mazurenko. / S.B.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 2001. / Includes bibliographical references (p. 126-136). / A dilute gas Bose-Einstein condensate was probed and manipulated by off-resonant laser beams. Spontaneous and stimulated off-resonant light scatterings were studied experimentally. Stimulated, two-photon Bragg scattering was used for spectroscopic measurement of the mean-field energy and of the intrinsic momentum uncertainty of the condensate. The high momentum and energy resolution of this method allowed the determination of the coherence length of the condensate, which was shown to be equal to its size. Spontaneous, off-resonant Rayleigh scattering was studied by exposing an elongated condensate to a single off-resonant laser beam. Highly directional scattering of light and atoms was observed. This collective light scattering is shown to be directly analogous to Dicke superradiance, where the electronic coherence is replaced by the coherent center-of-mass motion of the atoms in the condensate. Superradiant Rayleigh scattering was used to amplify atomic matter waves. The active medium was a Bose-Einstein condensate, pumped by off-resonant laser light ("Dressed condensate"). An atomic wave packet was amplified with a gain of 10 to 100. Phase-coherence of the amplifier was verified by observing the interference of the output wave with a reference wave packet. Optical properties of the dressed condensate were also characterized, focusing on the key role of long-lived matter wave gratings produced by interference between the condensate at rest and the recoiling atoms. The narrow bandwidth for the optical gain gave rise to an extremely slow group velocity of an amplified light pulse ([approx.] 1 m/s). / (cont.) The role of quantum statistics in these enhanced scatterings was studied. It was shown that the macroscopic occupation of a single quantum state is not necessary. These processes are in principle possible for fermionic or non-degenerate samples, provided the atomic ensemble has a sufficiently long coherence time. By moving a focused, far off-resonant laser beam through a condensate, vortex excitations were created in a Bose-Einstein condensate. They were observed as dislocations in the interference fringes formed by the stirred condensate and a second unperturbed condensate. The technique was shown to be a powerful tool to study turbulent superfluid flow. / by Shin Inouye. / Ph.D.

Thesis (B.S.) Massachusetts Institute of Technology. Dept. of Physics, 1950. / MIT copy bound with: Radio frequency generator for atomic beam experiments / Richard T. Daly, Jr. 1950. / Bibliography: leaf 23. / by Lawrence Gould. / B.S.

Thesis: S.B., Massachusetts Institute of Technology, Department of Physics, 2015. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 103-105). / Quantum field theory is the most well-developed tool in theoretical physics to study about the dynamics at microscopic scales, with particles and quantum behaviors. In this thesis I'll review about the construction of quantum field theory from the S-matrix point of view (building up particles and formulating interactions), then poke at interesting topics that are usually briefly mentioned or even ignored in standard quantum theory of field textbooks. In more details, chapter 1 will be about how a quanta is defined from the analysis of group theory, chapter 2 will be focus on how the language of field to describe the quantum behaviors of quanta is desirable for interactions and arised quite naturally (it should be noted that, string theory can be viewed as a totally different theory in quantum interactions, with conformal symmetric and topological natures, but at low energy scale it can always be reduced back to quantum field theories), and chapter 3 will be about several angles of quantum field theory. / by Trung Van Phan. / S.B.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Physics, 2018. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 123-130). / This thesis presents the experimental work on building a quantum gas microscope, employing fermionic 40K atoms in an optical lattice, and precision control of the atoms under the microscope. This system works as a natural simulator of the 2D Hubbard model, which describes materials with strongly correlated electrons. After preparing ultracold 40K atoms in an optical lattice and performing Raman sideband cooling, single lattice site resolution was obtained. Metallic, Mott insulating, and band insulating states were observed in situ and local moment was directly accessed as a local observable with the site-resolved imaging. Performing spin-selective imaging also gave access to spin, and spatial correlations of charge and spin was measured with respect to doping. In this measurements, antiferromagnetic correlations were observed in the spin sector. In the charge sector, we observed an anti-bunching behavior at low fillings, as a result of the Pauli exclusion principle and repulsive interactions. We also observed that doublon-hole bunching resulting from the superexchange excitations dominates and causes the charges to bunch. In order to increase the simulation capabilities, we updated the microscope with arbitrary optical potential imprinting ability. Using a digital micromirror device (DMD), a 2D box potential was created with the sharpness of a few lattice sites. A homogenous 2D Hubbard system is created at half-filling in this box potential. Using a magnetic gradient, different spin states were separated within a Mott insulator, being an ideal starting point for performing spin transport measurements. The lowest energy s-wave Feshbach resonance between 19/2, -7/2) and 19/2, -5/2) states of 40K was characterized with an increased precision and established as an interaction varying knob of our quantum simulator. Interaction energy spectrum around this resonance was measured. Confinement induced molecules on the attractive side and deeply bound molecules on the repulsive side are observed in an optical lattice. / by Melih Okan. / Ph. D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 1998. / Includes bibliographical references (p. 139-143). / by Ian Maxwell Avruch. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 1996. / Includes bibliographical references (p. 191-196). / by Lam Hui. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 1996. / Includes bibliographical references (p. 127-132). / by Darren Thomas Garnier. / Ph.D.

Thesis: S.B., Massachusetts Institute of Technology, Department of Physics, 2014. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 37-38). / Nuclear correlation functions reveal interesting physical properties of atomic nuclei, including ground state energies and scattering potentials. However, calculating their values is computationally intensive due to the fact that the number of terms from quantum chromodynamics in a nuclear wave function scales exponentially with atomic number. In this thesis, we demonstrate two methods for speeding up this computation. First, we represent a correlation function as a sum of the determinants of many small matrices, and exploit similarities between the matrices to speed up the calculations of the determinants. We also investigate representing a correlation function as a sum of functions of bipartite graphs, and use isomorph-free exhaustive generation techniques to find a minimal set of graphs that represents the computation. / by Pranjal Vachaspati. / S.B.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Physics, 2015. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 64-72). / I discuss several novel topological phases in correlated electron systems, realized through spin-orbit interactions and lattice effects especially narrow-band systems. The first realizes the fractional quantum Hall effect using geometric frustration and ferromagnetism to obtain a nearly flat band with a large bandgap and non-zero Chern number. This system can support this effect at high temperatures upon partial filling of the flat band. The second proposal builds upon this system: as the ground state is a fractional quantum Hall state, excitations of this state are anyons when there is an incommensurate filling. The underlying lattice allows access to a new regime in which the anyon gas can form a charged superfluid, including states with intrinsic topological order or that similar to a BCS-type state. The third proposal studies topological crystalline insulators and strain as an effective gauge field on the surface state Dirac fermions. The zero-energy Landau orbitals form a flat band where the high density of states gives rise to the interface superconductivity observed in IV-VI semiconductor multilayers at high temperatures, with non-BCS behavior. A discussion of superconductivity in flat band systems concludes and is contrasted with classic results for a typical electron gas. This work closely parallels that in references [1, 2, 3]. / by Evelyn Tang. / Ph. D.