4,189 research outputs found
Psychiatry and molecular genetics: a paradigm shift.
The late 20th century is witnessing an explosion of biomedical knowledge in the discipline of molecular genetics. In this regard many medical specialties will be transformed in terms of diagnosis and treatment. The technology and the recent clinical research in psychiatry is one of these
Heralded Two-Photon Entanglement from Probabilistic Quantum Logic Operations on Multiple Parametric Down-Conversion Sources
An ideal controlled-NOT gate followed by projective measurements can be used
to identify specific Bell states of its two input qubits. When the input qubits
are each members of independent Bell states, these projective measurements can
be used to swap the post-selected entanglement onto the remaining two qubits.
Here we apply this strategy to produce heralded two-photon polarization
entanglement using Bell states that originate from independent parametric
down-conversion sources, and a particular probabilistic controlled-NOT gate
that is constructed from linear optical elements. The resulting implementation
is closely related to an earlier proposal by Sliwa and Banaszek
[quant-ph/0207117], and can be intuitively understood in terms of familiar
quantum information protocols. The possibility of producing a ``pseudo-demand''
source of two-photon entanglement by storing and releasing these heralded pairs
from independent cyclical quantum memory devices is also discussed.Comment: 5 pages, 4 figures; submitted to IEEE Journal of Selected Topics in
Quantum Electronics, special issue on "Quantum Internet Technologies
Quantum reflection of atoms from a solid surface at normal incidence
We observed quantum reflection of ultracold atoms from the attractive
potential of a solid surface. Extremely dilute Bose-Einstein condensates of
^{23}Na, with peak density 10^{11}-10^{12}atoms/cm^3, confined in a weak
gravito-magnetic trap were normally incident on a silicon surface. Reflection
probabilities of up to 20 % were observed for incident velocities of 1-8 mm/s.
The velocity dependence agrees qualitatively with the prediction for quantum
reflection from the attractive Casimir-Polder potential. Atoms confined in a
harmonic trap divided in half by a solid surface exhibited extended lifetime
due to quantum reflection from the surface, implying a reflection probability
above 50 %.Comment: To appear in Phys. Rev. Lett. (December 2004)5 pages, 4 figure
The Vortex Phase Qubit: Generating Arbitrary, Counter-Rotating, Coherent Superpositions in Bose-Einstein Condensates via Optical Angular Momentum Beams
We propose a scheme for generation of arbitrary coherent superposition of
vortex states in Bose-Einstein condensates (BEC) using the orbital angular
momentum (OAM) states of light. We devise a scheme to generate coherent
superpositions of two counter-rotating OAM states of light using known
experimental techniques. We show that a specially designed Raman scheme allows
transfer of the optical vortex superposition state onto an initially
non-rotating BEC. This creates an arbitrary and coherent superposition of a
vortex and anti-vortex pair in the BEC. The ideas presented here could be
extended to generate entangled vortex states, design memories for the OAM
states of light, and perform other quantum information tasks. Applications to
inertial sensing are also discussed.Comment: 4 pages, 4 figures, Revtex4, to be submitted to Phys. Rev. Let
Optical interface created by laser-cooled atoms trapped in the evanescent field surrounding an optical nanofiber
Trapping and optically interfacing laser-cooled neutral atoms is an essential
requirement for their use in advanced quantum technologies. Here we
simultaneously realize both of these tasks with cesium atoms interacting with a
multi-color evanescent field surrounding an optical nanofiber. The atoms are
localized in a one-dimensional optical lattice about 200 nm above the nanofiber
surface and can be efficiently interrogated with a resonant light field sent
through the nanofiber. Our technique opens the route towards the direct
integration of laser-cooled atomic ensembles within fiber networks, an
important prerequisite for large scale quantum communication schemes. Moreover,
it is ideally suited to the realization of hybrid quantum systems that combine
atoms with, e.g., solid state quantum devices
Local and Global Distinguishability in Quantum Interferometry
A statistical distinguishability based on relative entropy characterises the
fitness of quantum states for phase estimation. This criterion is employed in
the context of a Mach-Zehnder interferometer and used to interpolate between
two regimes, of local and global phase distinguishability. The scaling of
distinguishability in these regimes with photon number is explored for various
quantum states. It emerges that local distinguishability is dependent on a
discrepancy between quantum and classical rotational energy. Our analysis
demonstrates that the Heisenberg limit is the true upper limit for local phase
sensitivity. Only the `NOON' states share this bound, but other states exhibit
a better trade-off when comparing local and global phase regimes.Comment: 4 pages, in submission, minor revision
Quantum Clock Synchronization Based on Shared Prior Entanglement
We demonstrate that two spatially separated parties (Alice and Bob) can
utilize shared prior quantum entanglement, and classical communications, to
establish a synchronized pair of atomic clocks. In contrast to classical
synchronization schemes, the accuracy of our protocol is independent of Alice
or Bob's knowledge of their relative locations or of the properties of the
intervening medium.Comment: 4 page
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