2,087 research outputs found
Strongly Coupled Plasmas via Rydberg-Blockade of Cold Atoms
We propose and analyze a new scheme to produce ultracold neutral plasmas deep
in the strongly coupled regime. The method exploits the interaction blockade
between cold atoms excited to high-lying Rydberg states and therefore does not
require substantial extensions of current ultracold plasma experiments.
Extensive simulations reveal a universal behavior of the resulting Coulomb
coupling parameter, providing a direct connection between the physics of
strongly correlated Rydberg gases and ultracold plasmas. The approach is shown
to reduce currently accessible temperatures by more than an order of magnitude,
which opens up a new regime for ultracold plasma research and cold ion-beam
applications with readily available experimental techniques.Comment: 5 pages, 5 figure
Degenerate quantum gases of strontium
Degenerate quantum gases of alkaline-earth-like elements open new
opportunities in research areas ranging from molecular physics to the study of
strongly correlated systems. These experiments exploit the rich electronic
structure of these elements, which is markedly different from the one of other
species for which quantum degeneracy has been attained. Specifically,
alkaline-earth-like atoms, such as strontium, feature metastable triplet
states, narrow intercombination lines, and a non-magnetic, closed-shell ground
state. This review covers the creation of quantum degenerate gases of strontium
and the first experiments performed with this new system. It focuses on
laser-cooling and evaporation schemes, which enable the creation of
Bose-Einstein condensates and degenerate Fermi gases of all strontium isotopes,
and shows how they are used for the investigation of optical Feshbach
resonances, the study of degenerate gases loaded into an optical lattice, as
well as the coherent creation of Sr_2 molecules.Comment: Review paper, 43 pages, 24 figures, 249 reference
Accessing Rydberg-dressed interactions using many-body Ramsey dynamics
We demonstrate that Ramsey spectroscopy can be used to observe
Rydberg-dressed interactions. In contrast to many prior proposals, our scheme
operates comfortably within experimentally measured lifetimes, and accesses a
regime where quantum superpositions are crucial. The key idea is to build a
spin-1/2 from one level that is Rydberg-dressed and another that is not. These
levels may be hyperfine or long-lived electronic states. An Ising spin model
governs the Ramsey dynamics, for which we derive an exact solution. Due to the
structure of Rydberg interactions, the dynamics differs significantly from that
in other spin systems. As one example, spin echo can increase the rate at which
coherence decays. The results also apply to bare (undressed) Rydberg states as
a special case, for which we quantitatively reproduce recent ultrafast
experiments without fitting
Emergence of Kinetic Behavior in Streaming Ultracold Neutral Plasmas
We create streaming ultracold neutral plasmas by tailoring the photoionizing
laser beam that creates the plasma. By varying the electron temperature, we
control the relative velocity of the streaming populations, and, in conjunction
with variation of the plasma density, this controls the ion collisionality of
the colliding streams. Laser-induced fluorescence is used to map the spatially
resolved density and velocity distribution function for the ions. We identify
the lack of local thermal equilibrium and distinct populations of
interpenetrating, counter-streaming ions as signatures of kinetic behavior.
Experimental data is compared with results from a one-dimensional, two-fluid
numerical simulation.Comment: 8 pages, 6 figure
Ultracold Neutral Plasmas
Ultracold neutral plasmas, formed by photoionizing laser-cooled atoms near
the ionization threshold, have electron temperatures in the 1-1000 kelvin range
and ion temperatures from tens of millikelvin to a few kelvin. They represent a
new frontier in the study of neutral plasmas, which traditionally deals with
much hotter systems, but they also blur the boundaries of plasma, atomic,
condensed matter, and low temperature physics. Modelling these plasmas
challenges computational techniques and theories of non-equilibrium systems, so
the field has attracted great interest from the theoretical and computational
physics communities. By varying laser intensities and wavelengths it is
possible to accurately set the initial plasma density and energy, and
charged-particle-detection and optical diagnostics allow precise measurements
for comparison with theoretical predictions. Recent experiments using optical
probes demonstrated that ions in the plasma equilibrate in a strongly coupled
fluid phase. Strongly coupled plasmas, in which the electrical interaction
energy between charged particles exceeds the average kinetic energy, reverse
the traditional energy hierarchy underlying basic plasma concepts such as Debye
screening and hydrodynamics. Equilibration in this regime is of particular
interest because it involves the establishment of spatial correlations between
particles, and it connects to the physics of the interiors of gas-giant planets
and inertial confinement fusion devices.Comment: 89 pages, 54 image
Creating Non-Maxwellian Velocity Distributions in Ultracold Plasmas
We present techniques to perturb, measure and model the ion velocity
distribution in an ultracold neutral plasma produced by photoionization of
strontium atoms. By optical pumping with circularly polarized light we promote
ions with certain velocities to a different spin ground state, and probe the
resulting perturbed velocity distribution through laser-induced fluorescence
spectroscopy. We discuss various approaches to extract the velocity
distribution from our measured spectra, and assess their quality through
comparisons with molecular dynamic simulationsComment: 13 pages, 8 figure
Velocity Relaxation in a Strongly Coupled Plasma
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.Comment: 5 pages, 5 figure
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