Publications (10)0 Total impact
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Article: Zeeman relaxation of cold atomic iron and nickel in collisions with^{3} He
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ABSTRACT: We have measured the ratio γ of the diffusion cross section to the angular momentum reorientation cross section in the colliding Fe-3He and Ni-3He systems. Nickel (Ni) and iron (Fe) atoms are introduced via laser ablation into a cryogenically cooled experimental cell containing cold (<1 K) 3He buffer gas. Elastic collisions rapidly cool the translational temperature of the ablated atoms to the 3He temperature. γ is extracted by measuring the decays of the atomic Zeeman sublevels. For our experimental conditions, thermal energy is comparable to the Zeeman splitting. As a result, thermal excitations between Zeeman sublevels significantly impact the observed decay. To determine γ accurately, we introduce a model of Zeeman-state dynamics that includes thermal excitations. We find γNi-3He=5×103 and γFe-3He⩽3×103 at 0.75 K in a 0.8-T magnetic field. These measurements are interpreted in the context of submerged shell suppression of spin relaxation, as studied previously in transition metals and rare-earth-metal atoms [ C. I. Hancox, S. C. Doret, M. T. Hummon, R. V. Krems and J. M. Doyle Phys. Rev. Lett. 94 013201 (2005); C. I. Hancox, S. C. Doret, M. T. Hummon, L. Luo and J. M. Doyle Nature (London) 431 281 (2004); A. Buchachenko, G. Chaasiski and M. Szczniak Eur. Phys. J. D 45 147 (2007)].Phys. Rev. A. 06/2010; 81(6). -
Article: Zeeman Relaxation of Cold Atomic Iron and Nickel in Collisions with 3He
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ABSTRACT: We have measured the ratio of the diffusion cross-section to the angular momentum reorientation cross-section in the colliding Fe-3He and Ni-3He systems. Nickel (Ni) and iron (Fe) atoms are introduced via laser ablation into a cryogenically cooled experimental cell containing cold (< 1 K) 3He buffer gas. Elastic collisions rapidly cool the translational temperature of the ablated atoms to the helium temperature. The cross-section ratio is extracted by measuring the decays of the atomic Zeeman sublevels. For our experimental conditions, thermal energy is comparable to the Zeeman splitting. As a result, thermal excitations between Zeeman sublevels significantly impact the observed decay. To determine the cross-section ratio accurately, we introduce a model of Zeeman state dynamics that includes thermal excitations. We find the cross-section ratio for Ni-3He = 5 x 10^3 and Fe-3He <= 3 x 10^3 at 0.75 K in a 0.8 T magnetic field. These measurements are interpreted in the context of submerged shell suppression of spin relaxation as studied previously in transition metals and rare earth atoms. Comment: 10 pages, 5 figures; submitted to Phys. Rev. A03/2010; -
Article: Inelastic Collision Rates of Trapped Metastable Hydrogen
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ABSTRACT: We report the first detailed decay studies of trapped metastable (2S) hydrogen. By two-photon excitation of ultracold H samples, we have produced clouds of at least 5x10^7 magnetically trapped 2S atoms at densities greater than 4x10^10 cm^-3 and temperatures below 100 \muK. We derive experimental values for the total 2S-2S two-body loss rate constant in this temperature regime. Our results are in the range of recent theoretical calculations. We also find experimental upper limits on the rate constant for loss due to inelastic 1S-2S collisions. Comment: Submitted to Phys. Rev. A. Pre-print format: 21 pages, 8 figures10/2002; -
Article: S-2S Spectroscopy of Trapped Hydrogen: The Cold Collision Frequency Shift and Studies of BEC
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ABSTRACT: The cold collision frequency shift of the 1S-2S two-photon transition is studied in trapped spin-polarized atomic hydrogen at submillikelvin temperatures. This effect is the low temperature manifestation of the pressure shift and broadening familiar from spectroscopy at normal temperatures and pressures. We find the shift is given by Delta 1S Gamma2S = Gamma3:8 Sigma 0:8 Theta 10 Gamma10 n Hz cm 3 , where n is the sample density. Theory is developed to express the shift in terms of the mean field interaction energy due to collisions and thus relate it to the s-wave triplet scattering lengths, a 1S Gamma1S and a 1S Gamma2S . From this we derive a 1S Gamma2S = Gamma1:4 Sigma 0:3 nm, which is in fair agreement with a recent calculation. 1S-2S spectroscopy is a valuable probe of the density, temperature, and atomatom interactions in the trapped sample, especially in the regime of Bose-Einstein condensation (BEC). We describe properties of the condensate and how they are determined from the 1S-2S spectrum. Thesis Supervisor: Thomas J. Greytak Title: Professor of Physics Thesis Supervisor: Daniel Kleppner Title: Lester Wolfe Professor of Physics Acknowledgments Graduate school has been the best time of my life and I owe that to Amy Salzhauer. She always shares my excitement when things go well and is ready with a reassuring smile when progress seems slow or nonexistent. She has a talent for getting me out of the lab to enjoy the rest of life, and my experience at MIT has been richer because I have had someone with which to share it. For as long as I can remember my parents have encouraged me to ask questions, take risks, and explore the world around me, and those lessons have served me well. My family may not have understood why I spent the last five y...08/2001; -
Article: Macroscopicorde From Reversible and Stochastic Lattice Growth Models
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ABSTRACT: This thesis advances the understanding of how autonomous microscopic physical processes give rise to macroscopic structure. A unifying theme is the use of physically motivated microscopic models of discrete systems which incorporate the constraints of locality, uniformity, and exact conservation laws. The features studied include: stochastic nonequilibrium fluctuations; use of pseudorandomness in dynamical simulations; the thermodynamics of pattern formation; recurrence times of finite discrete systems; and computation in physical models. I focus primarily on pattern formation: transitions from a disordered to an ordered macroscopic state. Using an irreversible stochastic model of pattern formation in an open system driven by an external source of noise, I study thin film growth. I focus on the regimes of growth and the average properties of the resulting rough surfaces. I also show that this model couples sensitively to the imperfections of various pseudorandom number generators...07/2000; -
Article: Bose-Einstein Condensation of Atomic Hydrogen
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ABSTRACT: We have observed Bose-Einstein condensation (BEC) of trapped atomic hydrogen, and studied it by two-photon spectroscopy of the 1S-2S transition. In these lecture notes we briefly review the history of spin-polarized atomic hydrogen and describe the final steps to BEC. Laser spectroscopy, which probes the difference in mean field energy of the 1S and 2S states, is used to study the condensate, which has a peak density of 4.8e15 cm^-3 and population of 10^9.01/1999; -
Article: Bose-Einstein Condensation of Atomic Hydrogen
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ABSTRACT: We report observation of Bose-Einstein condensation of a trapped, dilute gas of atomic hydrogen. The condensate and normal gas are studied by two-photon spectroscopy of the 1S-2S transition. Interactions among the atoms produce a shift of the resonance frequency proportional to density. The condensate is clearly distinguished by its large frequency shift. The peak condensate density is 4.8 +/- 1.1 \times 10^{15} cm^{-3}, corresponding to a condensate population of 10^9 atoms. The BEC transition occurs at about T=50 uK and n=1.8 \times 10^{14} cm^{-3}. Comment: Accepted for publication in PRL; 9 pages, 4 PostScript figures, ReVTeX. Updated discussion of degeneracy effects09/1998; -
Article: Cold Collision Frequency Shift of the 1S-2S Transition in Hydrogen
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ABSTRACT: We have observed the cold collision frequency shift of the 1S-2S transition in trapped spin-polarized atomic hydrogen. We find $\Delta \nu_{1S-2S} = -3.8(8)\times 10^{-10} n Hz cm^3$, where $n$ is the sample density. From this we derive the 1S-2S s-wave triplet scattering length, $a_{1S-2S}=-1.4(3)$ nm, which is in fair agreement with a recent calculation. The shift provides a valuable probe of the distribution of densities in a trapped sample. Comment: Accepted for publication in PRL, 9 pages, 4 PostScript figures, ReVTeX. Updated connection of our measurement to theoretical work09/1998; -
Article: Spin‐polarized hydrogen: New possibilities for polarized sources and targets
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ABSTRACT: The creation of spin‐polarized atomic hydrogen (H↓) points the way to improved methods for producing polarized proton sources and targets. The systematics of H↓ are reviewed and applications are outlined for an intense H− source, a polarized atomic jet, and gaseous and solid targets. A technique is proposed for producing solid polarized deuterium for use in a fusion reactor plasma, or as a polarized target.AIP Conference Proceedings. 03/1983; 95(1):546-565. -
Article: Magnetic relaxation in dysprosium-dysprosium collisions
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ABSTRACT: The collisional magnetic reorientation rate constant gR is measured for magnetically trapped atomic dysprosium (Dy), an atom with large magnetic dipole moments. Using buffer gas cooling with cold helium, large numbers (>1011) of Dy are loaded into a magnetic trap and the buffer gas is subsequently removed. The decay of the trapped sample is governed by collisional reorientation of the atomic magnetic moments. We find gR=1.9±0.5×10-11 cm3 s-1 at 390 mK. We also measure the magnetic reorientation rate constant of holmium (Ho), another highly magnetic atom, and find gR=5±2×10-12 cm3 s-1 at 690 mK. The Zeeman relaxation rates of these atoms are greater than expected for the magnetic dipole-dipole interaction, suggesting that another mechanism, such as an anisotropic electrostatic interaction, is responsible. Comparison with estimated elastic collision rates suggests that Dy is a poor candidate for evaporative cooling in a magnetic trap.Phys. Rev. A. 83(1).
Top co-authors
Institutions
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1983–2010
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Massachusetts Institute of Technology
- Department of Physics
Cambridge, MA, USA
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