Browsing by Author "Hulet, Randall G"
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Item Decoherence of Matter-Wave Breathers in Lithium Bose Einstein-Condensates(2024-07-09) Jin, Eva; Hulet, Randall GThe experimental work presented in this thesis studies and characterizes decoherence of excited matter-wave solitons, known as breathers, in neutral lithium-7 BECs. Motivated by the rich pool of theoretical predictions for beyond mean-field physics, and recent work in our lab which experimentally realized the production of breathers, we study the lifetime and decay of breathers in a one-dimensional (1D) wave guide. We report measurements of decoherence and dissociation of breathers in a quasi- 1D geometry, and attribute the dissociation features to three-body loss by comparing against numerical results from the 1D Gross-Pitaevskii (GP) simulations in the mean- field approximation. We find that in the low atomic density regime for breathers, breathers no longer dissociate and deviate from the GP simulation results. In this regime, the breather damps out and embodies signatures of relaxation associated with beyond mean-field number fluctuations.Item Design of a high numerical aperture vacuum chamber for 3D optical lattice experiments(2022-04-21) Singh, Bhagwan; Hulet, Randall GThe next generation of 3D optical lattice experiments requires a new vacuum chamber design. In the past, a 3D optical lattice apparatus in our lab was used to create and observe antiferromagnetic (AFM) coorelations within a 6Li-based degenerate Fermi gas. In that experiment, implementing anti-trapping beams overlapped with the standard lattice beams allowed the potential landscape to be made smoother, in an effort to increase the spatial extent of the AFM phase. Nevertheless, preparing atoms to be even cooler, and further extending the region of interest requires newer solutions. One method is to use the anti-trapping beams in a slightly different manner. By utilizing a higher numerical aperture optical beam line for anti-trapping, finer adjustments can be made in the potential. Combined with digital-micromirror based holography techniques. the anti-trapping beams can be custom-shaped to carve even finer details into the optical lattice. With sufficient control over beamshaping, one could perform better entropy re-distribution within the atom cloud. In this way, the central AFM region can be made colder by pushing entropy out to the wings. In this thesis, I will detail the work done in analyzing and designing a new chamber to fulfill the previously mentioned features.Item Dynamical Response of an Interacting 1-Dimensional Fermi Gas(2018-05-10) Yang, Tsung-Lin; Hulet, Randall GUltracold atoms with optical lattices provide a highly tunable system to measure the dynamic structure factor, $S(q,\omega)$, of an interacting one-dimensional (1D) Fermi gas. We use the two lowest hyperfine levels of the $^6$Li atom to form a pseudo-spin-1/2 system whose interactions are tunable via a Feshbach resonance. Bragg spectroscopy is used to measure the dynamic response of the 1D system to density (``charge'') mode excitations at a momentum $q$ and frequency $\omega$. In this thesis, we provide a quantitative comparison between the experimental result and the theoretical calculations based on Tomonaga-Luttinger theory.Item Overcoming Decoherence to Observe Quantum Fluctuations in Matter-Wave Breathers(2023-12-04) Espinoza Masbernat, Ricardo; Hulet, Randall GThe description of quantum many-body phenomena that go beyond a mean-field approximation is often difficult or, more typically, impossible to achieve. Experiments in this regime are also challenging due to technological constraints. An exception may be the dissociation of matter-wave breathers, which in 1D are exactly integrable solutions of the mean-field Gross-Pitaevskii equation, by quantum fluctuations. Breathers are coherent superpositions of fundamental solitons. To study these effects on the decoherence of 7Li matter-wave breathers, we first characterize the decoherence due to mean-field phenomena in quasi-1D. We find that mean-field decoherence of breathers is caused primarily by density-dependent atom loss. We also find that the mechanisms of atom loss present in our experiment, i.e. inelastic collisions with background gas and three-body recombination, have different effects on breather coherence. After identifying the sources of mean-field decoherence, we seek to suppress them so that dissociation by quantum fluctuations may be observable. For this purpose, we present a theoretical proposal and its experimental implementation aimed at enhancing the measure of breather dissociation, i.e. the relative distance between constituent solitons, via expansion in an anti-trapping harmonic potential.Item Second-Harmonic Generation for Narrow-Line Cooling of 7Li(2017-02-14) Luo, Henry; Hulet, Randall GLaser cooling of lithium atoms is usually performed on the 2S1/2 to 2P3/2 transition at 671 nm. The Doppler temperature of this transition, which is the limit temperature of laser cooling, is 140 µK. The 2S1/2 to 3P3/2 transition at 323 nm has a Doppler temperature 7 times smaller than that of the 671 nm transition. With the 323 nm transition, it is possible to reach a temperature low enough for an all-optical production of a Bose-Einstein condensate. The 323 nm light is produced by second-harmonic generation (SHG). We present our design of the laser system that generates light at 646 nm and the frequency-doubling cavity for SHG. The laser frequency is stabilized by a Fabry-Perot cavity and an Iodine transition.Item Spin-charge separation in a 1D Fermi gas with tunable interactions(2022-12-01) Cavazos Cavazos, Danyel Eduardo; Hulet, Randall GInteracting fermions that are confined to 1D can only support collective excitations and are thus governed by the Tomonaga-Luttinger liquid (TLL) theory, in which collective excitations decouple into charge and spin modes instead of particle-like excitations. Over the course of this work we have realized analog quantum simulations of the TLL model using a 6-Li atomic system. By taking advantage of a magnetic Feshbach resonance we readily tune the interactions of the sample so that we can transition from a non-interacting gas to either a strongly repulsive or a strongly attractive system, and probe the dynamics of the system within these regimes. By using low-momentum Bragg spectroscopy we were able to measure and characterize the spin-charge separation of a TLL. Our work also presents the first observation of spin and charge density waves that are separately excited from the ground state through a Bragg perturbation. The observed dynamical response function of the spin and charge excitations remarkably captures both the universal behavior of the Tomonaga-Luttinger liquid, as well as the non-linear effects related to the band curvature effect in the charge sector and the back-scattering interaction effect in the spin sector. Up to now considering higher-order corrections to the linear dispersion in either the spin or charge degrees of freedom had remained out of reach for both theory and experiment. In addition to this, we also realized a spin-incoherent Luttinger liquid and characterized its temperature crossover between the coherent and incoherent regimes. On the attractive interactions regime we observe an inversion of spin-charge separation, and we also have seen preliminary signatures of confinement-induced 1D bound states.Item The Search For FFLO in a Quasi-One-Dimensional Ultracold Fermi Gas(2022-04-20) Fry, Jacob Alexander; Hulet, Randall GThe Fulde-Ferrell Larkin-Ovchinnikov (FFLO) type superconductor is an exotic form of matter known as a supersolid because it simultaneously supports superfluid and magnetic order. In both condensed matter and ultracold atomic gases, this phase has yet to be conclusively observed despite long interest in both theory and experiment. In one-dimension (1D), unlike expectations for higher dimensions, the FFLO phase is found in a large region of the phase diagram [1]. The effect of quantum and thermal fluctuations, however, are expected to be reduced in higher dimensions. These considerations motivated the proposal to search for FFLO near the 1D-3D dimensional crossover [2], which we have identified and characterized [3]. We confine a spin-imbalanced Fermi gas of lithium 6 to an array of 1D tubes using a 2D optical lattice. We bring the system into the dimensional crossover by increasing the inter-tube tunneling rate and using a Feshbach resonance to tune interactions. The periodicity of these domain walls, which depends on the magnitude of the polarization, is a definitive signature of the FFLO phase. In this work, we develop new experimental and analytical methods to extract periodic signals that, if they indeed are domain walls, lay the foundation for full confirmation of the FFLO phase. [1] Y. A. Liao, A. S. C. Rittner, T. Paprotta, W. Li, G. B. Partridge, R. G. Hulet, S. K. Baur, and E. J. Mueller, “Spin-imbalance in a one-dimensional Fermi gas,” Nature 467, 567 (2010). [2] M. M. Parish, S. K. Baur, E. J. Mueller, and D. A. Huse, “Quasi-One- Dimensional Polarized Fermi Superfluids,” Phys. Rev. Lett. 99, 250403 (2007). [3] M. C. Revelle, J. A. Fry, B. A. Olsen, and R. G. Hulet, “1D to 3D Crossover of a Spin-Imbalanced Fermi Gas,” Physical Review Letters 117 (2016).Item Ultralong-Range Molecules and Rydberg Blockade in Ultracold 84Sr(2015-07-30) DeSalvo, Brian J.; Killian, Thomas C; Hulet, Randall G; Brooks, Philip RMy dissertation describes experiments on two-photon excitation of ultracold Sr to the 3S1 Rydberg series and represents the first experiments exciting Rydberg atoms via an intermediate triplet excited state. Due to the narrow linewidth (7.5 kHz) of the 1S0 – 3P1 transition in Sr, this excitation scheme yields longer coherence times and less loss from the intermediate state compared to methods using the usual dipole allowed transitions. This is advantageous for realizing the possibility of Rydberg dressing, where a small amount of Rydberg character is admixed to ground state atoms allowing for continuously tunable long-range interactions. With this goal in mind, we explore the interplay of Rydberg blockade, Rydberg-Rydberg interactions, and ground-Rydberg interactions in high density, ultracold gases through Autler-Townes spectroscopy and photoassociation of ultralong-range Rydberg molecules.