Download 2004 Term 1 January

Physics News off the Web compiled by John O’Connor, Past Federal President
of AIP
Highlights:
 The relativity of time has been affirmed with new higher precision
 Is the universe a dodecahedron?
 A new type of medium interface features negative refraction
AN ULTRABRIGHT TUNABLE PHOTON-PAIR SOURCE created at MIT is the
best generator so far of entangled photon pairs, a development which should help
quantum communications systems to do their job more smoothly. Entangled photons
possess a special correlation unlike anything in classical physics: if, say, we measure
the spin (polarization) of one photon, then we automatically know the polarization of
the other photon, even though it might be on the other side of the galaxy and even if,
until the moment of measurement, the spins of both photons had been indeterminate.
This weird property of quantum reality, it is hoped, will be a boon to encryption
(perhaps in a "quantum teleportation" scheme---see Physics News Update 350,
http://www.aip.org/enews/physnews/1997/split/pnu350-1.htm ) and future quantum
computers. Indeed, for some time now quantum effects have been an important factor
in communications engineering applications, especially insofar as quantum
fluctuations (uncertainty in our knowledge of where an electron is or the value of its
energy) can produce levels of electrical noise that can limit the effectiveness of
practical devices. The use of entangled photons might be able to mitigate this
problem. Quantum limitations are already a problem in such devices as optical
amplifiers (whose amplified spontaneous emission noise limits communication
performance) or soliton pulses (supposedly non-dispersing light pulses that are subject
to quantum-induced timing jitter accumulation) used in fiber-optic communications.
MIT's Research Laboratory of Electronics is a place where quantum aspects of
electrical engineering are taken very seriously. The head of the lab, Jeffrey H.
Shapiro ([email protected], 617-253-4179), will report on progress in a program aimed at
developing a system for long-distance, high-fidelity teleportation of photon states at
the upcoming Frontiers in Optics meeting of the Optical Society of America. As part
of this work the MIT team has developed a source of entangled photons some ten
times brighter than previous sources. The correlated photons are engendered by
shooting a laser beam into a nonlinear optical crystal, where incoming photons are, in
effect, split into two related photons of half the wavelength. This "down-conversion"
process is even tunable over a certain wavelength range. Up to 12,000 photon pairs
per second per milliwatt of input power have been produced. (Paper MI3, OSA
meeting 5-9 October in Tucson, AZ; meeting website at
http://www.osa.org/meetings/annual/ )
THE RELATIVITY OF TIME, as set forth in Einstein's theory, has been affirmed
once again, with new higher precision. Time dilation is the name for the notion that
elapsed time as recorded by two observers with identical clocks will differ if one of
the observers is travelling at a velocity v with respect to the other. The amount of
dilation will become more noticeable as v becomes a larger fraction of the speed of
light. In an experiment performed by Gerald Gwinner, Dirk Schwalm and their
colleagues at the Max Planck Institute for Nuclear Physics in Heidelberg the clocks
are lithium ions. The ions are struck by laser light from in front and from the back,
putting them temporarily into an excited state and inducing fluorescence. By
comparing the resonant laser wavelengths with the transition wavelength of the
stationary ion, and by taking into account the Doppler effect (the apparent wavelength
of a wave emitted from a travelling source will always be different from a stationary
source owing to bunching or thinning of the wave crests---but this has nothing to do
with relativity) the researchers can arrive at a value for time dilation. In the
Heidelberg experiment, the lithium ions moved with a speed of 19,000 km/sec, or
about 6.4 % of the speed of light (and corresponding to an energy of 13.3 MeV, the
largest energy obtainable at the local heavy-ion storage ring). The precision of the
new time dilation measurement, an uncertainty of 2.2 x 10^-7, is about a factor of four
better than the best previous value. (Saathoff et al., Physical Review Letters,
upcoming article; contact Guido Saathoff, [email protected]; website at http://www.mpi-hd.mpg.de/ato/rel/)
Physicist shares Nobel prize for medicine (Oct 6)
http://physicsweb.org/article/news/7/10/3
Sir Peter Mansfield, a physicist at Nottingham University in the UK, has been
awarded the 2003 Nobel Prize in Physiology or Medicine. Mansfield shares the prize
with Paul Lauterbur of the University of Illinois in the US "for their discoveries
concerning magnetic resonance imaging". Mansfield and Lauterbur laid the
foundations for magnetic resonance imaging (MRI) in the 1970s. The technique is
now widely used to image the brain and other organs, with more than 60 million MRI
examinations being carried out in hospitals last year.
Nobel prize goes to low-temperature theorists (Oct 7)
http://physicsweb.org/article/news/7/10/4
The 2003 Nobel Prize in Physics has been shared by three theorists "for their
pioneering contributions to the theory of superconductors and superfluidity". Alexei
Abrikosov of the Argonne National Laboratory in the US, Vitaly Ginzburg of the P N
Lebedev Physical Institute in Moscow and Anthony Leggett of the University of
Illinois at Urbana have all made substantial contributions to a wide range of topics in
theoretical physics over their careers. Abrikosov and Ginzburg are honoured for their
work on so-called type-II superconductors, while Leggett is recognized for his work
on the theory of superfluidity in helium-3.
Is the universe a dodecahedron? (Oct 8)
http://physicsweb.org/article/news/7/10/5
The standard model of cosmology predicts that the universe is infinite and flat.
However, cosmologists in France and the US are now suggesting that space could be
finite and shaped like a dodecahedron instead. They claim that a universe with the
same shape as the twelve-sided polygon can explain measurements of the cosmic
microwave background - the radiation left over from the big bang - that spaces with
more mundane shapes cannot (J-P Luminet et al. 2003 Nature 425 593).
Darmstadt gets credit for new elements (Oct 9)
http://physicsweb.org/article/news/7/10/6
The discovery of element 111 has been officially credited to the GSI laboratory in
Darmstadt, Germany, by a joint working party set up by the International Union of
Pure and Applied Chemistry (IUPAC) and the sister union for physics (IUPAP).
IUPAC has also officially approved a proposal from GSI that element 110 - which
was also discovered at the German lab - should be known as darmstadtium (Ds).
COSMOLOGY THEORIES COME AND GO as new information becomes
available. The geometry and nature of the universe must be one of the most
fascinating questions for the human species. Early Egyptians thought the universe
was a rectangular box. Alexandrian Greeks pictured the cosmos as a set of concentric
crystalline spheres, a view adopted by the medieval Catholic Church, which executed
Giordano Bruno for holding that the universe was infinite in extent. In the 20th
century Hubble's surveys of receding galaxies supported the idea of an expanding
spacetime scaffolding. This model, now called the big bang, is generally the accepted
overarching theory, but it has been amended several times to include an early
"inflationary" phase and, more recently, the existence of dark energy, an entity or
mechanism which apparently allows the expansion of the universe visible to our
telescopes to be speeding up, and not slowing down. Also not slowing down is the
list of new cosmological ideas. Last year's entrant was the "ekpyrotic" model
(http://www.aip.org/enews/physnews/2002/split/588-2.html ), according to which our
universe and all the energy and matter bresiding therein arises from the collision of
two immense membranes embedded in an even larger multi-dimensional volume.
Last week's interesting new cosmology development was the suggestion that the
universe is finite and has a dodecahedral (soccerball) geometry (Luminet et al.,
Nature, 9 October 2003). Meanwhile, this week's leading cosmology news, presented
at a meeting in Cleveland, featured observations of very distant (8 to 10 billion light
years away) and unusually bright supernovas, recorded by the Hubble Space
Telescope. This accords with the dark energy model which holds that the general
expansion of the universe was relatively slow 10 billion years ago and afterwards got
much faster, owing to the propulsive effects of the dark energy winning out over the
attractive and slowing effects of gravity (paper by Adam Reiss,
http://www.phys.cwru.edu/events/cosmol03.php; also see Science News Online, 11
October ).
A use of Synchrotron radiation in research
WHY DON'T ALCOHOL AND WATER MIX VERY WELL? Bartenders who
make cocktails shouldn't worry about trying to get alcohol and water to mix
completely. Nature prevents even the most patient drink-makers from fully blending
the two. Studying methanol, a simple non-drinkable alcohol that nonetheless can
provide insights into ethanol, or drinking alcohol, a US-Swedish collaboration
(Jinghua Guo, LBL, 510-495-2230, [email protected]) has obtained new molecular-level
details of why water and alcohol don't mix very well. Using LBL's Advanced Light
Source, the researchers performed x-ray emission (XE) and x-ray absorption (XA)
spectroscopy, which allowed them to study such things as the chemical bonds that
form between molecules in the liquid over timescales of picoseconds to
femtoseconds. Looking first at a liquid of pure methanol, the researchers observed
the presence of rings and chains made of 6-8 methanol molecules. When they mixed
methanol and water, they found that the 6-8 molecule chains connected with water
molecules to form larger water/methanol clusters (see image at
http://www.aip.org/mgr/png/2003/203.htm ). These clusters are very stable, because
of the (hydrogen) chemical bonds that hold them together. But the water/methanol
clusters also have a high amount of order, thereby reducing the liquid's overall
disorder (entropy). Yet entropy must stay the same or increase in the liquid. So
nature discourages the formation of more clusters in the liquid, and this can explain
why alcohol and water don't like to mix completely. In addition, the research sheds
light on a 40-year controversy over the molecular structure of pure methanol liquid,
and the structures that are formed when water and methanol combine. For example,
other researchers had suggested that water surrounded methanol in a static, ice-like
structure. (Guo et al., Physical Review Letters, 10 October 2003).
A NEW TYPE OF MEDIUM INTERFACE FEATURES NEGATIVE
REFRACTION or, depending on the angle of incidence, positive (conventional)
refraction. This switch-hitting optical ability (the technical name for it is
"amphoteric" refraction) is a first. Furthermore, the same type of interface can be
used to refract (negative or positive) a ballistic beam of electrons (electrons traveling,
as waves, over a very short distance in a straight line). Refraction, a change in
direction, is what happens when light waves (or other kinds of waves) move from a
material with one index of refraction (say, air) into a medium (water, say) with a
different index. Physicists at the National Renewable Energy Lab in Colorado have
devised their material sample not from a collection of tiny rods and split rings
mounted on boards, as was the case with previously reported negative-refraction
materials. Instead they used a YVO4 bicrystal. Negative-refraction materials are also
called "left handed materials," or LHM, because they refract light in a way which is
contrary to the normal "right handed" rules of electromagnetism (for a past summary
in Update, see http://www.aip.org/enews/physnews/2003/split/628-1.html ). LHM
researchers hope that the peculiar properties will lead to superior lenses, and might
provide a chance to observe some kind of negative analog of other prominent optical
phenomena, such as the Doppler shift and Cerenkov radiation. According to Yong
Zhang (303-384-6617, [email protected]), an additional feature of their material is
that it inhibits all reflection. When considering the refraction process, reflection can
be thought of as a sort of energy-loss penalty paid by waves when they are refracted,
and so a reflection-less lens would be of enormous value in, for example, the transport
of high-power laser beams. (Zhang et al., Physical Review Letters, 10 October 2003;
see figure at http://www.aip.org/mgr/png/2003/202.htm)