Physics News Update no. 588

May 14 2002 @ 03:18 by Phil Schewe, James Riordon, and Ben Stein

This news bulleting reports in the first observation of bright bolitions in a BOSE-Einstein condensate, a parallell, dark-matter universe, and the creation of a tungsten photonic crystal.

The American Institute of Physics Bulletin of Physics
Number 588, May 9, 2002

Bright Solitons in a Bose-Einstein Condensate
Bright solitons in a Bose-Einstein condensate have been created and observed for the first time by a Rice University team (Randy Hulet, 713-348-6087, randy@atomcool.rice.edu), yielding a stunning new demonstration of the wavelike behavior of atoms and providing an important tool for eventual technological applications of BECs.

First observed on the surface of a narrow canal in 1834, a soliton is a group of waves combining in such a way to form a single composite wave that can travel for long distances without spreading out or losing its original shape.

Solitons can occur in all kinds of waves; for example, they have been thoroughly studied in sound waves and light waves. In fact, soliton light waves are currently employed in telecommunications.

Solitons can exist in BECs too. Since a BEC consists of ultracold atoms all in the same quantum state, it exhibits wavelike behavior and therefore can be considered as a single atom wave. However, the BEC atom wave usually spreads apart or "disperses" shortly after the BEC is released from a trap.

Nonetheless, in previous BEC experiments (such as Burger et al., Phys. Rev. Lett., 20 December 1999), researchers have observed "dark solitons," representing absences of atoms that can propagate without changing shape in a condensate.

Now, in a BEC of lithium atoms, the Rice team has produced "bright" solitons, each representing a condensate of actual atoms extracted from the main BEC. In effect, the bright solitons are individual atom waves broken off from the main BEC atom wave. Using a narrow laser beam to guide BEC atoms in a single-file line, the Rice team tailored the interactions between lithium atoms to be attractive so that the atoms' attraction for one another perfectly offset their predisposition to spread out.

With their technique, the Rice researchers have created "trains" of up to 15 solitons (see figure). These atom-wave solitons will likely be a useful tool someday for BEC versions of gyroscopes for ultra-precise navigation and very accurate atomic clocks (Strecker et al., Nature, 9 May 2002 print issue; this work will also be presented in papers G1.011 and R1.001 at the upcoming APS Division of Atomic, Molecular, and Optical Physics (DAMOP) meeting in Williamsburg from May 29-June 1.)

Another Universe Might Lurk Only Millimeters Away
Another universe might lurk only millimeters away from our universe, but we wouldn't know it because it exists on its own membrane separated from our membrane in some extra spatial dimension. Matter on the other membrane would be invisible but could exert a gravitational effect and would, in fact, constitute the "dark matter" for which astrophysicists have sought for some years.

In a recent paper Paul Steinhardt (Princeton) and Neil Turok (Cambridge) propose that the structure in our universe may well have come about in the collision of two such membrane universes. All the historical events in the life of our cosmos--initial big bang, subsequent expansion of galaxies, even the currently observed accelerated expansion phase, and finally a contraction into a "big crunch"--would be played out in a recurring drama.

This cyclic cosmology (an extension of Steinhardt's "ekpyrosis" theory; see Update 535) uses all the latest tools of string theory, accounts for the "dark energy" supposedly firing cosmic acceleration, and would have no need for an ad-hoc "inflationary" phase appended to the standard big bang model to explain such cosmological features such as the horizon problem (why the extreme edges of the visible universe seem to be at the same temperature). (Sciencexpress, 25 April, soon to be in Science.)

Tungsten Photonic Crystal
Shawn Lin and his colleagues at Sandia have made a photonic crystal, a lattice of atoms that excludes light at certain wavelengths, out of tungsten. They did this creating a special semiconductor structure with conventional lithographic methods, then removing selectively some of the material and backfilling with a vapor of tungsten. Metal photonic crystals have been made before but the Sandia model is the first to operate (exclude light) over the range of 8 to 20 microns. By excluding light in this stretch of the infrared a lightbulb filament fashioned into a photonic crystal geometry might be much more efficient than existing versions by redirecting more energy into producing light rather than heat. (Fleming et al., Nature, 2 May 2002; also see Sandia news release.)

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