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{at}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-Universit„t 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{at}ruhr-uni-bochum.de
The Havenith lab's Web site

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