427 research outputs found
Hybrid quantum systems of atoms and ions
In recent years, ultracold atoms have emerged as an exceptionally
controllable experimental system to investigate fundamental physics, ranging
from quantum information science to simulations of condensed matter models.
Here we go one step further and explore how cold atoms can be combined with
other quantum systems to create new quantum hybrids with tailored properties.
Coupling atomic quantum many-body states to an independently controllable
single-particle gives access to a wealth of novel physics and to completely new
detection and manipulation techniques. We report on recent experiments in which
we have for the first time deterministically placed a single ion into an atomic
Bose Einstein condensate. A trapped ion, which currently constitutes the most
pristine single particle quantum system, can be observed and manipulated at the
single particle level. In this single-particle/many-body composite quantum
system we show sympathetic cooling of the ion and observe chemical reactions of
single particles in situ.Comment: ICAP proceeding
Cold heteronuclear atom-ion collisions
We study cold heteronuclear atom ion collisions by immersing a trapped single
ion into an ultracold atomic cloud. Using ultracold atoms as reaction targets,
our measurement is sensitive to elastic collisions with extremely small energy
transfer. The observed energy-dependent elastic atom-ion scattering rate
deviates significantly from the prediction of Langevin but is in full agreement
with the quantum mechanical cross section. Additionally, we characterize
inelastic collisions leading to chemical reactions at the single particle level
and measure the energy-dependent reaction rate constants. The reaction products
are identified by in-trap mass spectrometry, revealing the branching ratio
between radiative and non-radiative charge exchange processes
The impact of tree age on biomass growth and carbon accumulation capacity: A retrospective analysis using tree ring data of three tropical tree species grown in natural forests of Suriname
The world’s forests play a pivotal role in the mitigation of global climate change. By photosynthesis they remove CO2 from the atmosphere and store carbon in their biomass. While old trees are generally acknowledged for a long carbon residence time, there is no consensus on their contribution to carbon accumulation due to a lack of long-term individual tree data. Tree ring analyses, which use anatomical differences in the annual formation of wood for dating growth zones, are a retrospective approach that provides growth patterns of individual trees over their entire lifetime. We developed time series of diameter growth and related annual carbon accumulation for 61 trees of the species Cedrela odorata L. (Meliacea), Hymenaea courbaril L. (Fabacea) and Goupia glabra Aubl. (Goupiacea). The trees grew in unmanaged tropical wet-forests of Suriname and reached ages from 84 to 255 years. Most of the trees show positive trends of diameter growth and carbon accumulation over time. For some trees we observed fluctuating growth—periods of lower growth alternate with periods of increased growth. In the last quarter of their lifetime trees accumulate on average between 39 percent (C. odorata) and 50 percent (G. glabra) of their final carbon stock. This suggests that old-growth trees in tropical forests do not only contribute to carbon stocks by long carbon resistance times, but maintain high rates of carbon accumulation at later stages of their life time
On the transverse mode of an atom laser
The transverse mode of an atom laser beam that is outcoupled from a
Bose-Einstein condensate is investigated and is found to be strongly determined
by the mean--field interaction of the laser beam with the condensate. Since for
repulsive interactions the geometry of the coupling scheme resembles an
interferometer in momentum space, the beam is found show filamentation.
Observation of this effect would prove the transverse coherence of an atom
laser beam.Comment: 4 pages, 4 figure
Magnetic phases of one-dimensional lattices with 2 to 4 fermions per site
We study the spectral and magnetic properties of one-dimensional lattices
filled with 2 to 4 fermions (with spin 1/2) per lattice site. We use a
generalized Hubbard model that takes account all interactions on a lattice
site, and solve the many-particle problem by exact diagonalization. We find an
intriguing magnetic phase diagram which includes ferromagnetism, spin-one
Heisenberg antiferromagnetism, and orbital antiferromagnetism.Comment: 8 pages, 6 figure
Hybrid apparatus for Bose-Einstein condensation and cavity quantum electrodynamics: Single atom detection in quantum degenerate gases
We present and characterize an experimental system in which we achieve the
integration of an ultrahigh finesse optical cavity with a Bose-Einstein
condensate (BEC). The conceptually novel design of the apparatus for the
production of BECs features nested vacuum chambers and an in-vacuo magnetic
transport configuration. It grants large scale spatial access to the BEC for
samples and probes via a modular and exchangeable "science platform". We are
able to produce \87Rb condensates of five million atoms and to output couple
continuous atom lasers. The cavity is mounted on the science platform on top of
a vibration isolation system. The optical cavity works in the strong coupling
regime of cavity quantum electrodynamics and serves as a quantum optical
detector for single atoms. This system enables us to study atom optics on a
single particle level and to further develop the field of quantum atom optics.
We describe the technological modules and the operation of the combined BEC
cavity apparatus. Its performance is characterized by single atom detection
measurements for thermal and quantum degenerate atomic beams. The atom laser
provides a fast and controllable supply of atoms coupling with the cavity mode
and allows for an efficient study of atom field interactions in the strong
coupling regime. Moreover, the high detection efficiency for quantum degenerate
atoms distinguishes the cavity as a sensitive and weakly invasive probe for
cold atomic clouds
Electronic tuneability of a structurally rigid surface intermetallic and Kondo lattice: CePt / Pt(111)
We present an extensive study of structure, composition, electronic and
magnetic properties of Ce--Pt surface intermetallic phases on Pt(111) as a
function of their thickness. The sequence of structural phases appearing in low
energy electron diffraction (LEED) may invariably be attributed to a single
underlying intermetallic atomic lattice. Findings from both microscopic and
spectroscopic methods, respectively, prove compatible with CePt formation
when their characteristic probing depth is adequately taken into account. The
intermetallic film thickness serves as an effective tuning parameter which
brings about characteristic variations of the Cerium valence and related
properties. Soft x-ray absorption (XAS) and magnetic circular dichroism (XMCD)
prove well suited to trace the changing Ce valence and to assess relevant
aspects of Kondo physics in the CePt surface intermetallic. We find
characteristic Kondo scales of the order of 10 K and evidence for
considerable magnetic Kondo screening of the local Ce moments.
CePt/Pt(111) and related systems therefore appear to be promising
candidates for further studies of low-dimensional Kondo lattices at surfaces.Comment: 14 pages, 11 figure
Collapse and revival of oscillations in a parametrically excited Bose-Einstein condensate in combined harmonic and optical lattice trap
In this work, we study parametric resonances in an elongated cigar-shaped BEC
in a combined harmonic trap and a time dependent optical lattice by using
numerical and analytical techniques. We show that there exists a relative
competition between the harmonic trap which tries to spatially localize the BEC
and the time varying optical lattice which tries to delocalize the BEC. This
competition gives rise to parametric resonances (collapse and revival of the
oscillations of the BEC width). Parametric resonances disappear when one of the
competing factors i.e strength of harmonic trap or the strength of optical
lattice dominates. Parametric instabilities (exponential growth of Bogoliubov
modes) arise for large variations in the strength of the optical lattice.Comment: 9 pages, 20 figure
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