21 research outputs found
Zeeman Relaxation of Cold Atomic Iron and Nickel in Collisions with 3He
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.
Ponderomotive light squeezing with atomic cavity optomechanics
Accessing distinctly quantum aspects of the interaction between light and the
position of a mechanical object has been an outstanding challenge to
cavity-optomechanical systems. Only cold-atom implementations of cavity
optomechanics have indicated effects of the quantum fluctuations in the optical
radiation pressure force. Here we use such a system, in which quantum
photon-number fluctuations significantly drive the center of mass of an atomic
ensemble inside a Fabry-Perot cavity. We show that the optomechanical response
both amplifies and ponderomotively squeezes the quantum light field. We also
demonstrate that classical optical fluctuations can be attenuated by 26 dB or
amplified by 20 dB with a weak input pump power of < 40 pW, and characterize
the optomechanical amplifier's frequency-dependent gain and phase response in
both the amplitude and phase-modulation quadratures
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Formation and dynamics of van der Waals molecules in buffer-gas traps
We show that weakly bound He-containing van der Waals molecules can be produced and magnetically trapped in buffer-gas cooling experiments, and provide a general model for the formation and dynamics of these molecules. Our analysis shows that, at typical experimental parameters, thermodynamics favors the formation of van der Waals complexes composed of a helium atom bound to most open-shell atoms and molecules, and that complex formation occurs quickly enough to ensure chemical equilibrium. For molecular pairs composed of a He atom and an S-state atom, the molecular spin is stable during formation, dissociation, and collisions, and thus these molecules can be magnetically trapped. Collisional spin relaxation is too slow to affect trap lifetimes. However, 3He-containing complexes can change spin due to adiabatic crossings between trapped and untrapped Zeeman states, mediated by the anisotropic hyperfine interaction, causing trap loss. We provide a detailed model for Ag3He molecules, using ab initio calculation of Ag–He interaction potentials and spin interactions, quantum scattering theory, and direct Monte Carlo simulations to describe formation and spin relaxation in this system. The calculated rate of spin-change agrees quantitatively with experimental observations, providing indirect evidence for molecular formation in buffer-gas-cooled magnetic traps. Finally, we discuss the possibilities for spectroscopic detection of these complexes, including a calculation of expected spectra for Ag3He, and report on our spectroscopic search for Ag3He, which produced a null result.Astronom
Formation and dynamics of van der Waals molecules in buffer-gas traps
We show that weakly bound He-containing van der Waals molecules can be
produced and magnetically trapped in buffer-gas cooling experiments, and
provide a general model for the formation and dynamics of these molecules. Our
analysis shows that, at typical experimental parameters, thermodynamics favors
the formation of van der Waals complexes composed of a helium atom bound to
most open-shell atoms and molecules, and that complex formation occurs quickly
enough to ensure chemical equilibrium. For molecular pairs composed of a He
atom and an S-state atom, the molecular spin is stable during formation,
dissociation, and collisions, and thus these molecules can be magnetically
trapped. Collisional spin relaxations are too slow to affect trap lifetimes.
However, helium-3-containing complexes can change spin due to adiabatic
crossings between trapped and untrapped Zeeman states, mediated by the
anisotropic hyperfine interaction, causing trap loss. We provide a detailed
model for Ag3He molecules, using ab initio calculation of Ag-He interaction
potentials and spin interactions, quantum scattering theory, and direct Monte
Carlo simulations to describe formation and spin relaxation in this system. The
calculated rate of spin-change agrees quantitatively with experimental
observations, providing indirect evidence for molecular formation in
buffer-gas-cooled magnetic traps.Comment: 20 pages, 13 figure
Nathan Ukalović, klarinet : drugi dio diplomskog ispita
Drugi dio diplomskog ispita Nathana Ukalovića (klarinet), studenta Muzičke akademije u Zagrebu. Ispit je održan na Muzičkoj akademiji u dvorani "Stančić" 30.9.2021. Klavirska pratnja: Marina Matolić; mentor: Davor Reba. Program: 1. Gioacchino Rossini: Introdukcija, tema i varijacije za klarinet i orkestar; 2. Jörg Widmann: Fantasie; 3. Johannes Brahms: Sonata za klarinet op. 120, br. 2
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Magnetic Trapping of Silver and Copper, and Anomalous Spin Relaxation in the Ag-He System
We have trapped large numbers of copper (Cu) and silver (Ag) atoms using buffer-gas cooling. Up to 3×1012 Cu atoms and 4×1013 Ag atoms are trapped. Lifetimes are as long as 5 s, limited by collisions with the buffer gas. Ratios of elastic to inelastic collision rates with He are ≳106, suggesting Cu and Ag are favorable for use in ultracold applications. The temperature dependence of the Ag−He3 collision rate varies as T5.8±0.4. We find that this temperature dependence is inconsistent with the behavior predicted for relaxation arising from the spin-rotation interaction, and conclude that the Ag−He3 system displays anomalous collisional behavior in the multiple-partial wave regime. Gold (Au) was ablated into He3 buffer gas, however, atomic Au lifetimes were observed to be too short to permit trapping.Physic
Concerto en ré majeur : pour violon et orchestre Op. 77 / Johannes Brahms ; Nathan Milstein et The Pittsburgh Symphony; Orchestra dir. William Steinberg
Titre uniforme : [Concertos. Violon, orchestre. Op. 77. Ré majeur]BnF-Partenariats, Collection sonore - BelieveContient une table des matière