Vortex Proliferation in the Berezinskii-Kosterlitz-Thouless Regime on a Two-Dimensional Lattice of Bose-Einstein Condensates

We observe the proliferation of vortices in the Berezinskii-Kosterlitz-Thouless regime on a two-dimensional array of Josephson-coupled Bose-Einstein condensates. As long as the Josephson (tunneling) energy J exceeds the thermal energy T, the array is vortex free. With decreasing J/T, vortices appear in the system in ever greater numbers. We confirm thermal activation as the vortex-formation mechanism and obtain information on the size of bound vortex pairs as J/T is varied

Visible and Ultraviolet Laser Spectroscopy of ThF

The molecular ion ThF$^+$ is the species to be used in the next generation of search for the electron's Electric Dipole Moment (eEDM) at JILA. The measurement requires creating molecular ions in the eEDM sensitive state, the rovibronic ground state $^3\Delta_1$, $v^+=0$, $J^+=1$. Survey spectroscopy of neutral ThF is required to identify an appropriate intermediate state for a Resonance Enhanced Multi-Photon Ionization (REMPI) scheme that will create ions in the required state. We perform broadband survey spectroscopy (from 13000 to 44000~cm$^{-1}$) of ThF using both Laser Induced Fluorescence (LIF) and $1+1'$ REMPI spectroscopy. We observe and assign 345 previously unreported vibronic bands of ThF. We demonstrate 30\% efficiency in the production of ThF$^+$ ions in the eEDM sensitive state using the $\Omega = 3/2$ [32.85] intermediate state. In addition, we propose a method to increase the aforementioned efficiency to $\sim$100\% by using vibrational autoionization via core-nonpenetrating Rydberg states, and discuss theoretical and experimental challenges. Finally, we also report 83 vibronic bands of an impurity species, ThO.Comment: 49 pages, 7 figure

Laser-induced fluorescence studies of HfF+ produced by autoionization

Autoionization of Rydberg states of HfF, prepared using the optical-optical double resonance (OODR) technique, holds promise to create HfF+ in a particular Zeeman level of a rovibronic state for an electron electric dipole moment (eEDM) search. We characterize a vibronic band of Rydberg HfF at 54 cm-1 above the lowest ionization threshold and directly probe the state of the ions formed from this vibronic band by performing laser-induced fluorescence (LIF) on the ions. The Rydberg HfF molecules show a propensity to decay into only a few ion rotational states of a given parity and are found to preserve their orientation qualitatively upon autoionization. We show empirically that we can create 30% of the total ion yield in a particular |J+,M+> state and present a simplified model describing autoionization from a given Rydberg state that assumes no angular dynamics.Comment: 8 pages, 5 figure

Precision Spectroscopy of Polarized Molecules in an Ion Trap

Polar molecules are desirable systems for quantum simulations and cold chemistry. Molecular ions are easily trapped, but a bias electric field applied to polarize them tends to accelerate them out of the trap. We present a general solution to this issue by rotating the bias field slowly enough for the molecular polarization axis to follow but rapidly enough for the ions to stay trapped. We demonstrate Ramsey spectroscopy between Stark-Zeeman sublevels in 180Hf19F+ with a coherence time of 100 ms. Frequency shifts arising from well-controlled topological (Berry) phases are used to determine magnetic g-factors. The rotating-bias-field technique may enable using trapped polar molecules for precision measurement and quantum information science, including the search for an electron electric dipole moment.Comment: Accepted to Scienc

Berry-Like Phases in Structured Atoms and Molecules

Quantum mechanical phases arising from a periodically varying Hamiltonian are considered. These phases are derived from the eigenvalues of a stationary, “dressed” Hamiltonian that is able to treat internal atomic or molecular structure in addition to the time variation. In the limit of an adiabatic time variation, the usual Berry phase is recovered. For more rapid variation, nonadiabatic corrections to the Berry phase are recovered in perturbation theory, and their explicit dependence on internal structure emerges. Simple demonstrations of this formalism are given, to particles containing interacting spins, and to molecules in electric fields

Alkali Adsorbate Polarization on Conducting and Insulating Surfaces Probed with Bose-Einstein Condensates

A magnetically trapped 87Rb Bose-Einstein condensate is used as a sensitive probe of short-range electrical forces. In particular, the electric polarization of, and the subsequent electric field generated by, 87Rb adsorbates on conducting and insulating surfaces is measured by characterizing perturbations to the magnetic trapping potential using high quality factor condensate excitations. The nature of the alterations to the electrical properties of Rb adsorbates is studied on titanium (metal) and silicon (semiconductor) surfaces, which exhibit nearly identical properties, and on glass (insulator), which displays a smaller transitory electrical effect. The limits of this technique in detecting electrical fields and ramifications for measurements of short-range forces near surfaces are discussed

Effect of Cold Collisions on Spin Coherence and Resonance Shifts in a Magnetically Trapped Ultra-Cold Gas

We have performed precision microwave spectroscopy on ultracold 87Rbconfined in a magnetic trap, both above and below the Bose-condensation transition. The cold collision frequency shifts for both normal and condensed clouds were measured, which allowed the intrastate and interstate density correlations (characterized by sometimes controversial “factors of 2”) to be determined. Additionally, temporal coherence of the normal cloud was studied, and the importance of mean-field and velocity-changing collisions in preserving coherence is discussed

An Atom Michelson Interferometer on a Chip Using a Bose-Einstein Condensate

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, reflecting, and recombining of condensate atoms are achieved by a standing-wave light field having a wave vector aligned along the atom waveguide. A differential phase shift between the two arms of the interferometer is introduced by either a magnetic-field gradient or with an initial condensate velocity. Interference contrast is still observable at 20% with atom propagation time of 10 ms

Revealing buried information: Statistical processing techniques for ultracold gas image analysis

The techniques of principal and independent component analysis are applied to images of ultracold atoms. As an illustrative example, we present the use of these model-independent methods to rapidly determine the differential phase of a BEC interferometer from large sets of images of interference patterns. These techniques have been useful in the calibration of the experiment and in the investigation of phase randomization. The details of the algorithms are provided.Comment: v2: Many changes made to answer reviewer comments and improve clarity. 29 pages, 9 figures v3: Small change to emphasize role of models in result interpretation. 29 pages, 9 figure