2,082 research outputs found
Production of Long-Lived Ultracold Li2 Molecules from a Fermi gas
We create weakly-bound Li2 molecules from a degenerate two component Fermi
gas by sweeping a magnetic field across a Feshbach resonance. The atom-molecule
transfer efficiency can reach 85% and is studied as a function of magnetic
field and initial temperature. The bosonic molecules remain trapped for 0.5 s
and their temperature is within a factor of 2 from the Bose-Einstein
condensation temperature. A thermodynamical model reproduces qualitatively the
experimental findings
A smoothing monotonic convergent optimal control algorithm for NMR pulse sequence design
The past decade has demonstrated increasing interests in using optimal
control based methods within coherent quantum controllable systems. The
versatility of such methods has been demonstrated with particular elegance
within nuclear magnetic resonance (NMR) where natural separation between
coherent and dissipative spin dynamics processes has enabled coherent quantum
control over long periods of time to shape the experiment to almost ideal
adoption to the spin system and external manipulations. This has led to new
design principles as well as powerful new experimental methods within magnetic
resonance imaging, liquid-state and solid-state NMR spectroscopy. For this
development to continue and expand, it is crucially important to constantly
improve the underlying numerical algorithms to provide numerical solutions
which are optimally compatible with implementation on current instrumentation
and at same time are numerically stable and offer fast monotonic convergence
towards the target. Addressing such aims, we here present a smoothing
monotonically convergent algorithm for pulse sequence design in magnetic
resonance which with improved optimization stability lead to smooth pulse
sequence easier to implement experimentally and potentially understand within
the analytical framework of modern NMR spectroscopy
Measurement of interaction energy near a Feshbach resonance in a 6Li Fermi gas
We investigate the strongly interacting regime in an optically trapped Li
Fermi mixture near a Feshbach resonance. The resonance is found at G
in good agreement with theory. Anisotropic expansion of the gas is interpreted
by collisional hydrodynamics. We observe an unexpected and large shift (G)
between the resonance peak and both the maximum of atom loss and the change of
sign of the interaction energy.Comment: 4 pages, 4 figure
Photoassociative creation of ultracold heteronuclear 6Li40K* molecules
We investigate the formation of weakly bound, electronically excited,
heteronuclear 6Li40K* molecules by single-photon photoassociation in a
magneto-optical trap. We performed trap loss spectroscopy within a range of 325
GHz below the Li(2S_(1/2))+K(4P_(3/2)) and Li(2S_(1/2))+K(4P_(1/2)) asymptotic
states and observed more than 60 resonances, which we identify as rovibrational
levels of 7 of 8 attractive long-range molecular potentials. The long-range
dispersion coefficients and rotational constants are derived. We find large
molecule formation rates of up to ~3.5x10^7s^(-1), which are shown to be
comparable to those for homonuclear 40K_2*. Using a theoretical model we infer
decay rates to the deeply bound electronic ground-state vibrational level
X^1\Sigma^+(v'=3) of ~5x10^4s^(-1). Our results pave the way for the production
of ultracold bosonic ground-state 6Li40K molecules which exhibit a large
intrinsic permanent electric dipole moment.Comment: 6 pages, 4 figures, submitted to EP
The equation of state of ultracold Bose and Fermi gases: a few examples
We describe a powerful method for determining the equation of state of an
ultracold gas from in situ images. The method provides a measurement of the
local pressure of an harmonically trapped gas and we give several applications
to Bose and Fermi gases. We obtain the grand-canonical equation of state of a
spin-balanced Fermi gas with resonant interactions as a function of
temperature. We compare our equation of state with an equation of state
measured by the Tokyo group, that reveals a significant difference in the
high-temperature regime. The normal phase, at low temperature, is well
described by a Landau Fermi liquid model, and we observe a clear thermodynamic
signature of the superfluid transition. In a second part we apply the same
procedure to Bose gases. From a single image of a quasi ideal Bose gas we
determine the equation of state from the classical to the condensed regime.
Finally the method is applied to a Bose gas in a 3D optical lattice in the Mott
insulator regime. Our equation of state directly reveals the Mott insulator
behavior and is suited to investigate finite-temperature effects.Comment: 14 pages, 6 figure
Radiative pion capture by a nucleon
The differential cross sections for and are computed up to in heavy baryon chiral perturbation
theory (HBChPT). The expressions at and have no free
parameters. There are three unknown parameters at , low energy
constants of the HBChPT Lagrangian, which are determined by fitting to
experimental data. Two acceptable fits are obtained, which can be separated by
comparing with earlier dispersion relation calculations of the inverse process.
Expressions for the multipoles, with emphasis on the p-wave multipoles, are
obtained and evaluated at threshold. Generally the results obtained from the
best of the two fits are in good agreement with the dispersion relation
predictions.Comment: 24 pages, Latex, using RevTe
Upper bounds on the density of states of single Landau levels broadened by Gaussian random potentials
We study a non-relativistic charged particle on the Euclidean plane R^2
subject to a perpendicular constant magnetic field and an R^2-homogeneous
random potential in the approximation that the corresponding random Landau
Hamiltonian on the Hilbert space L^2(R^2) is restricted to the eigenspace of a
single but arbitrary Landau level. For a wide class of Gaussian random
potentials we rigorously prove that the associated restricted integrated
density of states is absolutely continuous with respect to the Lebesgue
measure. We construct explicit upper bounds on the resulting derivative, the
restricted density of states. As a consequence, any given energy is seen to be
almost surely not an eigenvalue of the restricted random Landau Hamiltonian.Comment: 16 pages, to appear in "Journal of Mathematical Physics
Bosons and Fermions near Feshbach resonances
Near Feshbach resonances, , systems of Bose and Fermi particles
become strongly interacting/dense. In this unitary limit both bosons and
fermions have very different properties than in a dilute gas, e.g., the energy
per particle approach a value times an universal many-body
constant. Calculations based upon an approximate Jastrow wave function can
quantitatively describe recent measurements of trapped Bose and Fermi atoms
near Feshbach resonances.
The pairing gap between attractive fermions also scales as
near Feshbach resonances and is a large fraction
of the Fermi energy - promising for observing BCS superfluidity in traps.
Pairing undergoes several transitions depending on interaction strength and the
number of particles in the trap and can also be compared to pairing in nuclei.Comment: Revised version extended to include recent molecular BEC-BCS result
Cold atom Clocks and Applications
This paper describes advances in microwave frequency standards using
laser-cooled atoms at BNM-SYRTE. First, recent improvements of the Cs
and Rb atomic fountains are described. Thanks to the routine use of a
cryogenic sapphire oscillator as an ultra-stable local frequency reference, a
fountain frequency instability of where
is the measurement time in seconds is measured. The second advance is a
powerful method to control the frequency shift due to cold collisions. These
two advances lead to a frequency stability of at 7\times 10^{-16}^{87}^{133}$Cs fountains.
Finally we give an update on the cold atom space clock PHARAO developed in
collaboration with CNES. This clock is one of the main instruments of the
ACES/ESA mission which is scheduled to fly on board the International Space
Station in 2008, enabling a new generation of relativity tests.Comment: 30 pages, 11 figure
Matter wave pulses characteristics
We study the properties of quantum single-particle wave pulses created by
sharp-edged or apodized shutters with single or periodic openings. In
particular, we examine the visibility of diffraction fringes depending on
evolution time and temperature; the purity of the state depending on the
opening-time window; the accuracy of a simplified description which uses
``source'' boundary conditions instead of solving an initial value problem; and
the effects of apodization on the energy width.Comment: 11 pages, 11 figure
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