Browsing by Author "DeSalvo, B.J."
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Item Bose-Einstein Condensation of 84Sr(American Physical Society, 2009) Martinez de Escobar, Y.N.; Mickelson, P.G.; Yan, M.; DeSalvo, B.J.; Nagel, S.B.; Killian, T.C.We report Bose-Einstein condensation of Sr84 in an optical dipole trap. Efficient laser cooling on the narrow intercombination line and an ideal s-wave scattering length allow the creation of large condensates (N0∼3×105) even though the natural abundance of this isotope is only 0.6%. Condensation is heralded by the emergence of a low-velocity component in time-of-flight images.Item Bose-Einstein condensation of 88Sr through sympathetic cooling with 87Sr(2010-05-05) Mickelson, P.G.; Martinez de Escobar, Y.N.; Yan, M.; DeSalvo, B.J.; Killian, T.C.We report Bose-Einstein condensation of Sr88, which has a small, negative s-wave scattering length (a88=−2a0). We overcome the poor evaporative cooling characteristics of this isotope by sympathetic cooling with Sr87 atoms. Sr87 is effective in this role despite the fact that it is a fermion because of the large ground-state degeneracy arising from a nuclear spin of I=9/2, which reduces the impact of Pauli blocking of collisions. We observe a limited number of atoms in the condensate (Nmax≈104) that is consistent with the value of a88 and the optical dipole trap parameters.Item Controlling Condensate Collapse and Expansion with an Optical Feshbach Resonance(American Physical Society, 2013) Yan, Mi; DeSalvo, B.J.; Ramachandhran, B.; Pu, H.; Killian, T.C.We demonstrate control of the collapse and expansion of an Sr88 Bose-Einstein condensate using an optical Feshbach resonance near the S01−P13 intercombination transition at 689 nm. Significant changes in dynamics are caused by modifications of scattering length by up to ±10abg, where the background scattering length of Sr88 is abg=−2a0 (1a0=0.053 nm). Changes in scattering length are monitored through changes in the size of the condensate after a time-of-flight measurement. Because the background scattering length is close to zero, blue detuning of the optical Feshbach resonance laser with respect to a photoassociative resonance leads to increased interaction energy and a faster condensate expansion, whereas red detuning triggers a collapse of the condensate. The results are modeled with the time-dependent nonlinear Gross-Pitaevskii equation.Item Degenerate Fermi Gas of 87Sr(2010-07-13) DeSalvo, B.J.; Yan, M.; Mickelson, P.G.; Martinez de Escobar, Y.N.; Killian, T.C.We report quantum degeneracy in a gas of ultracold fermionic Sr87 atoms. By evaporatively cooling a mixture of spin states in an optical dipole trap for 10.5 s, we obtain samples well into the degenerate regime with T/TF=0.26+0.05−0.06. The main signature of degeneracy is a change in the momentum distribution as measured by time-of-flight imaging, and we also observe a decrease in evaporation efficiency below T/TF∼0.5.Item Numerical modeling of collisional dynamics of Sr in an optical dipole trap(American Physical Society, 2011) Yan, M.; Chakraborty, R.; Mazurenko, A.; Mickelson, P.G.; Martinez de Escobar, Y.N.; DeSalvo, B.J.; Killian, T.C.We describe a model of inelastic and elastic collisional dynamics of atoms in an optical dipole trap that utilizes numerical evaluation of statistical mechanical quantities and numerical solution of equations for the evolution of number and temperature of trapped atoms. It can be used for traps that possess little spatial symmetry and when the ratio of trap depth to sample temperature is relatively small. We compare simulation results with experiments on Sr88 and Sr84, which have well-characterized collisional properties.Item Resonant Rydberg Dressing of Alkaline-Earth Atoms via Electromagnetically Induced Transparency(American Physical Society, 2016) Gaul, C.; DeSalvo, B.J.; Aman, J.A.; Dunning, F.B.; Killian, T.C.; Pohl, T.We develop an approach to generate finite-range atomic interactions via optical Rydberg-state excitation and study the underlying excitation dynamics in theory and experiment. In contrast to previous work, the proposed scheme is based on resonant optical driving and the establishment of a dark state under conditions of electromagnetically induced transparency (EIT). Analyzing the driven dissipative dynamics of the atomic gas, we show that the interplay between coherent light coupling, radiative decay, and strong Rydberg-Rydberg atom interactions leads to the emergence of sizable effective interactions while providing remarkably long coherence times. The latter are studied experimentally in a cold gas of strontium atoms for which the proposed scheme is most efficient. Our measured atom loss is in agreement with the theoretical prediction based on binary effective interactions between the driven atoms.Item Rydberg-blockade effects in Autler-Townes spectra of ultracold strontium(American Physical Society, 2016) DeSalvo, B.J.; Aman, J.A.; Gaul, C.; Pohl, T.; Yoshida, S.; Burgdörfer, J.; Hazzard, K.R.A.; Dunning, F.B.; Killian, T.C.; Rice Center for Quantum MaterialsWe present a combined experimental and theoretical study of the effects of Rydberg interactions on Autler-Townes spectra of ultracold gases of atomic strontium. Realizing two-photon Rydberg excitation via a long-lived triplet state allows us to probe the regime where Rydberg state decay presents the dominant decoherence mechanism. The effects of Rydberg interactions are observed in shifts, asymmetries, and broadening of the measured atom-loss spectra. The experiment is analyzed within a one-body density-matrix approach, accounting for interaction-induced level shifts and dephasing through nonlinear terms that approximately incorporate correlations due to the Rydberg blockade. This description yields good agreement with our experimental observations for short excitation times. For longer excitation times, the loss spectrum is altered qualitatively, suggesting additional dephasing mechanisms beyond the standard blockade mechanism based on pure van der Waals interactions.Item Trap losses induced by near-resonant Rydberg dressing of cold atomic gases(American Physical Society, 2016) Aman, J.A.; DeSalvo, B.J.; Dunning, F.B.; Killian, T.C.; Yoshida, S.; Burgdörfer, J.The near-resonant dressing of cold strontium gases and Bose-Einstein condensates contained in an optical dipole trap (ODT) with the 5s30s3S1 Rydberg state is investigated as a function of the effective two-photon Rabi frequency, detuning, and dressing time. The measurements demonstrate that a rapid decrease in the ground-state atom population in the ODT occurs even for weak dressing and when well detuned from resonance. This decrease is attributed to Rydberg atom excitation, which can lead to direct escape from the trap and to population of very long-lived 5s5p3P0,2 metastable states. The effects of interactions between Rydberg atoms, including those populated by blackbody radiation, are analyzed. The work has important implications when considering the use of Rydberg dressing to control the interactions between dressed ground-state atoms.Item Ultra-long-range Rydberg molecules in a divalent atomic system(American Physical Society, 2015) DeSalvo, B.J.; Aman, J.A.; Dunning, F.B.; Killian, T.C.; Sadeghpour, H.R.; Yoshida, S.; Burgdörfer, J.We report the creation of ultra-long-range Sr2 molecules comprising one ground-state 5s2 1S0 atom and one atom in a 5sns 3S1 Rydberg state for n ranging from 29 to 36. Molecules are created in a trapped ultracold atomic gas using two-photon excitation near resonant with the 5s5p 3P1 intermediate state, and their formation is detected through ground-state atom loss from the trap. The observed molecular binding energies are reproduced with the aid of first-order perturbation theory that utilizes a Fermi pseudopotential with effective s-wave and p-wave scattering lengths to describe the interaction between an excited Rydberg electron and a ground-state Sr atom.