Text 674, 103 rader
Skriven 2005-12-10 09:21:51 av Herman Trivilino (1:106/2000.7)
Ärende: PNU 754
===============
Physics News Update
Number 754, November 16, 2005
by Phil Schewe and Ben Stein

Hyper-Entangled Photon Pairs

Physicists at the University of Illinois at Urbana-Champaign have demonstrated
for the first time the entanglement of two objects not merely in one aspect of
their quantum natures, such as spin, but in a multitude of ways.

Entanglement is the quantum affinity between or among particles (such as atoms
or photons) in which the measurement of some property for one particle
automatically and instantaneously determines the corresponding property of the
other particle.

Take the case of two photons entangled with respect to polarization, the
orientation of the electric field associated with the photon. The photons,
until detected, have no spin orientation; this is the principle of quantum
indeterminacy. Indeed, both photons are said to be in a superposition of
arbitrary -- but parallel -- polarization states. Consequently, each photon has
a 50 percent likelihood of being measured to have any polarization state --
e.g., +45 or -45 degrees. If now one photon's polarization is measured to be
+45, then its entangled twin will surely also be polarized along +45, owing to
the way the photons are made in this setup.

One of the chief hopes of entanglement research is to exploit the superposition
idea and the entanglement idea for performing unusually fast quantum
computation. In the Illinois experiment, two photons, produced in a
"down-conversion" process whereby one photon enters an optical crystal and
sunders into two lesser-energy correlated daughter photons, are entangled not
just in terms of polarization, but also in a number of other ways: energy,
momentum, and orbital angular momentum (see PNU 721).

Actually, the photon pair can be produced in either of two crystals, and the
uncertainty in the production details of the individual photons is what
provides the ability to attain entanglement in all degrees of freedom.

Is it better to entangle two particles in ten ways or ten particles in two
ways? They're probably equivalent, says Paul Kwiat, leader of the Illinois
group, but for the purpose of quantum computing or communication it might be of
some advantage if multiple quantum bits (or qubits) of information can be
encoded in a single pair of entangled particles. Kwiat (217-333-9116,
kwiat@uiuc.edu) says that his lab detects a record two million entangled photon
pairs per second with ample determination of numerous properties, allowing a
complete characterization of the entanglement produced.

Barreiro et al., Physical Review Letters, upcoming article

North-Pacific "Boing" Attributed to Minke Whales

Human singers send their voice into the supporting medium of air. Whales send
their songs into ocean water. One particular song, a sort of fluttering echo,
or "boing," sound first heard by human listeners in the North Pacific Ocean in
the 1950s (and recorded by US Navy submarines) baffled scientists. Where was it
coming from? Only now have the sounds been identified as coming from minke
whales.

Shannon Rankin and Jay Barlow, scientists at the National Marine Fisheries
Service in La Jolla, California, have gathered hydrophone data in the body of
ocean between Mexico and Hawaii and combined this with visual sightings of the
marine mammals. Not only has the source been traced to minke whales, but the
songs seem to be somewhat different on either side of a certain longitude.

To the east, the boing sound is issued at a frequency of about 92 Hz and an
average duration of 3.6 seconds. The west boing, by contrast, consists of a
135-Hz vocalization with a duration of about 2.6 seconds. The acoustic trace is
both frequency modulated (FM) and amplitude modulated (AM).

Rankin and Barlow, Journal of the Acoustical Society of America, November 2005
Numerous whale sounds, including the boing, can be accessed on this NOAA Web
page

Quantum Solvent

Scientists at the Ruhr-Universität Bochum in Germany have performed
high-precision, ultracold chemical studies of nitrogen oxide (NO) molecules by
inserting them into droplets of liquid helium (see figure).

NO, Science magazine's "molecule of the year" for 1992, is important because of
its role in atmospheric chemistry and in signal transduction in biology. A
radical is a molecular entity (sometimes charged and sometimes neutral) which
enters into chemical reactions as a unit. To sharpen our understanding of this
important molecule and its reactions, it would be desirable to cool it down,
the better to observe its complex spectra of quantum levels corresponding to
various vibrational and rotational states.

In the new experiment, liquid helium is shot from a cold nozzle into vacuum.
The resultant balls, each containing about 3,000 atoms, are allowed to fall
into a pipe where NO molecules are lurking. The NO is totally enveloped and,
within its superfluid-helium cocoon at a temperature of about 0.4 Kelvin, it
spins freely. The helium acts provides a cold environment but does not interact
chemically with the NO molecules. Because of this a high-resolution infrared
spectrum of NO in fluids could be recorded for the first time.

NO has been observed before in the gas phase, but never before has such a high
resolution spectrum be seen in the helium environment.

Haeften et al., Physical Review Letters, 18 November 2005
Contact Martina Havenith, martina.havenith@ruhr-uni-bochum.de
The Havenith lab's Web site

---
 * Origin: Big Bang (1:106/2000.7)