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Efimov states
1 April 2006
H.C.Nagerl of the University of Innsbruck, Austria, and his
colleagues have for the first time observed three-particle bound
states, whose existence was predicted theoretically by V.I.Efimov
in 1970 (Yadernaya fizika 12 1080 (1970)) - in a rare example of
the complex three-body problem allowing an exact analytical
solution. A family of low-energy bound states arises for a system
of three identical particles if there is a strong enough resonance
between the pair forces involved. Interestingly, because of the
quantum-mechanical nature of this effect, three-particle states can
even exist in the absence of two-particle bound states. The size of
the three-particle system is much less than the absolute scattering
length |a|, and the three-particle interactions are universal in
character and independent of precisely how two particles interact
when close together. The researchers studied a degenerate gas of
cesium atoms held in an optical dipole trap at temperatures between
19.0 and 120.0nK. The scattering length was controlled using a
Feshbach resonance and could be varied over a wide range by varying
the external magnetic field. For a < 0, the Efimov states were
identified by a sharp increase in electron recombination losses in
the trap - presumably due to the three-atom system rapidly
decaying from the three-particle state to one involving a strongly
bound dimer plus an individual atom. At a temperature of 10 nK,
Efimov states appeared when the scattering length was -850 Bohr
radii. Another type of Efimov state arose for a > 0. In this case
recombination losses are much lower and exhibit in their spectrum
a recombination minimum, due to the destructive interference of the
three-particle system's quantum decay channels. The position of the
minimum agrees well with theoretical predictions. At a > 0, Efimov
states arise due to a Feshbach resonance between single atoms and
dimers and can be interpreted as a three-particle generalization of
the Feshbach resonance concept.
Source: Nature 440 315 (2006)
Quantum telecloning
1 April 2006
A experiment on `quantum telecloning' has been conducted for the
first time by a research team from Japan and the UK. Unlike
`quantum teleportation,' in this case information about a state is
sent to two, rather than one, receivers, and the input state is not
reproduced perfectly but with some errors due to Heisenberg's
uncertainty principle. Whereas quantum teleportation transfers the
state of a particle, what was transferred in the new experiment was
information about the amplitude and phase of a laser beam wave. The
beam was reproduced at two remote locations to within 58% - a
rather good result considering the theoretical limit of 66% for the
reproduction accuracy in such an experiment. Telecloning may have
applications in quantum communications and possibly in future
quantum computers.
Source: Phys. Rev. Lett. 96 060504 (2006)
A nanomotor
1 April 2006
An experiment involving the controlled rotation of a single
molecule has been conducted by a team of researchers from the
Netherlands. In this experiment, an asymmetric organic molecule
placed on the surface of - and forming carbon-carbon double bonds
with - a liquid-crystalline film underwent photo-isomerization
from the left-handed form to the right-handed form when irradiated
the with 365nm ultraviolet light and became left-handed again when
the light was switched off. Repeating this twice made the molecule
rotate through 360o in the plane of the film. The change in the
shape of the molecule produced rotation-induced structural changes
in the liquid crystal's surface profile. Importantly, small objects
placed on the crystal's surface, in particular a glass rod 10,000
times the size of the molecule itself, were forced into rotation as
a result.
Source: Nature 440 163 (2006)
Polarization of the cosmic microwave background
1 April 2006
Analysis of three years of WMAP satellite data has provided
improved values of cosmological parameters and the first reliable
information on the polarization of the cosmic microwave background
radiation. The WMAP observations covered the entire celestial
sphere and were performed with polarization-sensitive radiometers
at five frequencies between 23.0 and 94.0 MHz. To filter out radio
noises from galactic objects, an analysis of their sources was
performed in detail. Microwave background polarization may be due
both to primary gravitational waves and to scattering from gas
clouds at a later epoch of the first stars reionizing the universe.
The new observations have allowed a tight constraint on the
gravitational wave contribution and showed that reionization
occurred at higher redshifts than previously thought (implying
early star formation at an epoch when the Universe was about 400
million years old). The way the background radiation fluctuates is
best described by a model in which the Hubble constant is 73km/(s Mpc),
baryonic matter accounts for 4% of the total density, and dark
matter and dark matter, for 22% and 74%, respectively. It is also
shown that the spectral power exponent of the primordial density
perturbations that gave rise to galaxies is n=0.951, which is
somewhat less than the 1 of Harrison-Zeldovich's flat spectrum.
Thus, the WMAP observations have provided further support for those
inflation models predicting n < 1, while ruling out models with a
large contribution from the tensor perturbation mode (gravitational
waves).
Sources: astro-ph/0603449;
astro-ph/0603450
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The Extracts from the Internet is a section of Uspekhi Fizicheskih Nauk (Physics Uspekhi) the monthly rewiew journal of the current state of the most topical problems in physics and in associated fields. The presented News is devoted to the fundamental discoveries of physics and astrophysics. Permanent editor is Yu.N. Eroshenko. It is compiled from a multitude of Internet sources.
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