266 research outputs found
Robust long-distance entanglement and a loophole-free Bell test with ions and photons
Two trapped ions that are kilometers apart can be entangled by the joint
detection of two photons, each coming from one of the ions, in a basis of
entangled states. Such a detection is possible with linear optical elements.
The use of two-photon interference allows entanglement distribution without
interferometric sensitivity to the path length of the photons. The present
method of creating entangled ions also opens up the possibility of a
loophole-free test of Bell's inequalities.Comment: published versio
A bosonic Josephson junction controlled by a single trapped ion
We theoretically investigate the properties of a double-well bosonic
Josephson junction coupled to a single trapped ion. We find that the coupling
between the wells can be controlled by the internal state of the ion, which can
be used for studying mesoscopic entanglement between the two systems and to
measure their interaction with high precision. As a particular example we
consider a single Rb atom and a small Bose-Einstein condensate
controlled by a single Yb ion. We calculate inter-well coupling
rates reaching hundreds of Hz, while the state dependence amounts to tens of Hz
for plausible values of the currently unknown s-wave scattering length between
the atom and the ion. The analysis shows that it is possible to induce either
the self-trapping or the tunneling regime, depending on the internal state of
the ion. This enables the generation of large scale ion-atomic wavepacket
entanglement within current technology.Comment: 6 pages and 5 figures, including additional material. Accepted for
publication in Phys. Rev. Let
Focusing a deterministic single-ion beam
We focus down an ion beam consisting of single 40Ca+ ions to a spot size of a
few mum using an einzel-lens. Starting from a segmented linear Paul trap, we
have implemented a procedure which allows us to deterministically load a
predetermined number of ions by using the potential shaping capabilities of our
segmented ion trap. For single-ion loading, an efficiency of 96.7(7)% has been
achieved. These ions are then deterministically extracted out of the trap and
focused down to a 1sigma-spot radius of (4.6 \pm 1.3)mum at a distance of 257mm
from the trap center. Compared to former measurements without ion optics, the
einzel-lens is focusing down the single-ion beam by a factor of 12. Due to the
small beam divergence and narrow velocity distribution of our ion source,
chromatic and spherical aberration at the einzel-lens is vastly reduced,
presenting a promising starting point for focusing single ions on their way to
a substrate.Comment: 16 pages, 7 figure
Robust entanglement
It is common belief among physicists that entangled states of quantum systems
loose their coherence rather quickly. The reason is that any interaction with
the environment which distinguishes between the entangled sub-systems collapses
the quantum state. Here we investigate entangled states of two trapped Ca
ions and observe robust entanglement lasting for more than 20 seconds
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