1,467 research outputs found
Historical changes in caribou distribution and land cover in and around Prince Albert National Park: land management implications
In central Saskatchewan, boreal woodland caribou population declines have been documented in the 1940s and again in the 1980s. Although both declines led to a ban in sport hunting, a recovery was only seen in the 1950s and was attributed to wolf control and hunting closure. Recent studies suggest that this time, the population may not be increasing. In order to contribute to the conservation efforts, historical changes in caribou distribution and land cover types in the Prince Albert Greater Ecosystem (PAGE), Saskatchewan, were documented for the period of 1960s to the present. To examine changes in caribou distribution, survey observations, incidental sightings and telemetry data were collated. To quantify landscape changes, land cover maps were created for 1966 and 2006 using current and historic forest resources inventories, fire, logging, and roads data. Results indicate that woodland caribou are still found throughout the study area although their distribution has changed and their use of the National Park is greatly limited. Results of transition prob¬abilities and landscape composition analyses on the 1966 and 2006 land cover maps revealed an aging landscape for both the National Park and provincial crown land portions of the PAGE. In addition, increased logging and the development of extensive road and trail networks on provincial crown land produced significant landscape fragmentation for woodland caribou and reduced functional attributes of habitat patches. Understanding historical landscape changes will assist with ongoing provincial and federal recovery efforts for boreal caribou, forest management planning activities, and landscape restoration efforts within and beyond the Park boundaries
Interaction-free measurements by quantum Zeno stabilisation of ultracold atoms
Quantum mechanics predicts that our physical reality is influenced by events
that can potentially happen but factually do not occur. Interaction-free
measurements (IFMs) exploit this counterintuitive influence to detect the
presence of an object without requiring any interaction with it. Here we
propose and realize an IFM concept based on an unstable many-particle system.
In our experiments, we employ an ultracold gas in an unstable spin
configuration which can undergo a rapid decay. The object - realized by a laser
beam - prevents this decay due to the indirect quantum Zeno effect and thus,
its presence can be detected without interacting with a single atom. Contrary
to existing proposals, our IFM does not require single-particle sources and is
only weakly affected by losses and decoherence. We demonstrate confidence
levels of 90%, well beyond previous optical experiments.Comment: manuscript with 5 figures, 3 supplementary figure, 1 supplementary
not
Second Order Correlation Function of a Phase Fluctuating Bose-Einstein Condensate
The coherence properties of phase fluctuating Bose-Einstein condensates are
studied both theoretically and experimentally. We derive a general expression
for the N-particle correlation function of a condensed Bose gas in a highly
elongated trapping potential. The second order correlation function is analyzed
in detail and an interferometric method to directly measure it is discussed and
experimentally implemented. Using a Bragg diffraction interferometer, we
measure intensity correlations in the interference pattern generated by two
spatially displaced copies of a parent condensate. Our experiment demonstrates
how to characterize the second order correlation function of a highly elongated
condensate and to measure its phase coherence length.Comment: 22 pages, 5 figure
Analyzing a Bose polaron across resonant interactions
Recently, two independent experiments reported the observation of long-lived
polarons in a Bose-Einstein condensate, providing an excellent setting to study
the generic scenario of a mobile impurity interacting with a quantum reservoir.
Here, we expand the experimental analysis by disentangling the effects of trap
inhomogeneities and the many-body continuum in one of these experiments. This
makes it possible to extract the energy of the polaron at a well-defined
density as a function of the interaction strength. Comparisons with quantum
Monte-Carlo as well as diagrammatic calculations show good agreement, and
provide a more detailed picture of the polaron properties at stronger
interactions than previously possible. Moreover, we develop a semi-classical
theory for the motional dynamics and three-body loss of the polarons, which
partly explains a previously unresolved discrepancy between theory and
experimental observations for repulsive interactions. Finally, we utilize
quantum Monte-Carlo calculations to demonstrate that the findings reported in
the two experiments are consistent with each other
Satisfying the Einstein-Podolsky-Rosen criterion with massive particles
In 1935, Einstein, Podolsky and Rosen (EPR) questioned the completeness of
quantum mechanics by devising a quantum state of two massive particles with
maximally correlated space and momentum coordinates. The EPR criterion
qualifies such continuous-variable entangled states, where a measurement of one
subsystem seemingly allows for a prediction of the second subsystem beyond the
Heisenberg uncertainty relation. Up to now, continuous-variable EPR
correlations have only been created with photons, while the demonstration of
such strongly correlated states with massive particles is still outstanding.
Here, we report on the creation of an EPR-correlated two-mode squeezed state in
an ultracold atomic ensemble. The state shows an EPR entanglement parameter of
0.18(3), which is 2.4 standard deviations below the threshold 1/4 of the EPR
criterion. We also present a full tomographic reconstruction of the underlying
many-particle quantum state. The state presents a resource for tests of quantum
nonlocality and a wide variety of applications in the field of
continuous-variable quantum information and metrology.Comment: 8 pages, 7 figure
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