Browsing by Author "Pohl, T."

Now showing 1 - 7 of 7
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    Creating Non-Maxwellian Velocity Distributions in Ultracold Plasmas
    (arXiv, 2011) Castro, J.; Bannasch, G.; McQuillen, P.; Pohl, T.; Killian, T.C.; Rice Quantum Institute
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    Demonstrating universal scaling for dynamics of Yukawa one-component plasmas after an interaction quench
    (American Physical Society, 2016) Langin, T.K.; Strickler, T.; Maksimovic, N.; McQuillen, P.; Pohl, T.; Vrinceanu, D.; Killian, T.C.
    The Yukawa one-component plasma (OCP) model is a paradigm for describing plasmas that contain one component of interest and one or more other components that can be treated as a neutralizing, screening background. In appropriately scaled units, interactions are characterized entirely by a screening parameter, κ. As a result, systems of similar κ show the same dynamics, regardless of the underlying parameters (e.g., density and temperature). We demonstrate this behavior using ultracold neutral plasmas (UNPs) created by photoionizing a cold (T≤10 mK) gas. The ions in UNP systems are well described by the Yukawa model, with the electrons providing the screening. Creation of the plasma through photoionization can be thought of as a rapid quench of the interaction potential from κ=∞ to a final κ value set by the electron density and temperature. We demonstrate experimentally that the postquench dynamics are universal in κ over a factor of 30 in density and an order of magnitude in temperature. Results are compared with molecular-dynamics simulations. We also demonstrate that features of the postquench kinetic energy evolution, such as disorder-induced heating and kinetic-energy oscillations, can be used to determine the plasma density and the electron temperature.
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    Electron-Temperature Evolution in Expanding Ultracold Neutral Plasmas
    (2007-08-17) Gupta, P.; Laha, S.; Simien, C.E.; Gao, H.; Castro, J.; Killian, T.C.; Pohl, T.
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    Experimental Realization of an Exact Solution to the Vlasov Equations for an Expanding Plasma
    (2007-10-08) Laha, S.; Gupta, P.; Simien, C.E.; Gao, H.; Castro, J.; Pohl, T.; Killian, T.C.
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    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.
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    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 Materials
    We 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.
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    Velocity Relaxation in a Strongly Coupled Plasma
    (American Physical Society, 2012) Bannasch, G.; Castro, J.; McQuillen, P.; Pohl, T.; Killian, T.C.; Rice Quantum Institute
    Collisional relaxation of Coulomb systems is studied in the strongly coupled regime. We use an optical pump-probe approach to manipulate and monitor the dynamics of ions in an ultracold neutral plasma, which allows direct measurement of relaxation rates in a regime where common Landau-Spitzer theory breaks down. Numerical simulations confirm the experimental results and display non-Markovian dynamics at early times.