The laser’s wavelength must be very precisely tuned to the atom. One of the hardest problems physicists face in making BECs is keeping the laser tuned to the right frequency despite outside interference; even a car passing by on the road outside a lab may cause enough vibration to knock the laser out of its desired frequency. To make things worse, as the average speed of the atoms decreases and their energy level goes down, the desired Doppler shift changes, so the laser must be retuned to match the new “high” energy atoms. In order to account for motion from all directions, the lasers shine in on the atoms from opposite points on all three axes. Further, the magnetic trap is combined with an optical trap that pushes atoms back towards the center if they stray too far. This laser set-up is known as “optical molasses.”
The atoms are then cooled further through what is known as evaporative cooling. Essentially, evaporative cooling allows the faster, more energetic atoms to escape from the trap, leaving only the slowest, coolest, least energetic atoms behind. Of all the materials used, rubidium was the easiest to make into a BEC because its atoms are the largest—they achieve low velocities at the highest temperature (energy) because mass relates to energy (hydrogen was the hardest BEC to form, but researchers think it may have superior applications because of its small size). When the atoms get to the point where only ground state atoms are left, they coalesce into a Bose-Einstein Condensate, which behaves like a superatom. The first condensate consisted of 2000 atoms; some condensates have been created that are the size of a dime (several million atoms), but still behave as one giant atom.
Properties and Future Applications
Most research into Bose-Einstein Condensates serves as “basic” research—that is to say, it is more concerned with knowing more about the world in general than with implementing a specific technology. However, there are several potential uses for BECs. The most promising application is in etching. When BECs are fashioned into a beam, they are like a laser in their coherence. That is to say, both a laser and a BEC beam run “in lock step,” guaranteeing that an experimenter can know how a part of the beam will behave at every single location. This property of lasers has been used in the past for etching purposes. A BEC beam would have greater precision and energy than a laser because even at their low kinetic energy state, the massive particles would be more energetic than the massless photons. The major technological concerns with a BEC beam would be getting a clean enough environment for it to function repeatedly and reducing the cost of BEC creation enough to use BECs regularly in beams. However, BEC beams or “atom lasers” could produce precisely trimmed objects down to a very small scale—possibly a nanotech scale. Their practical limits will be found with experimentation.
In some ways, the atom laser works as the opposite of a laser. A laser can produce more photons from the atoms at hand, but an atom laser can only deal with the number of atoms it starts with. Rather than being knocked into an excited state, as atoms that emit laser photons are, BEC atoms are cooled down to the ground state. Unlike a laser beam, an atom laser beam could not travel far through air and would fall due to gravity. However, these differences can be calculated and accounted for in the future uses of the atom laser.
One of the most commonly known properties of BECs is their superfluidity. That is to say, BECs flow without interior friction. Since they’re effectively superatoms, BECs are all moving in the same way at the same time when they flow, and don’t have energy losses due to friction. Even the best lubricants currently available have some frictional losses as their molecules interact with each other, but BECs, while terribly expensive, would pose no such problem.
One of the problems physicists run into when teaching quantum mechanics is that the principles are just counter-intuitive. They’re hard to visualize. But videos of BEC blobs several millimeters across show wave-particle duality at a level we can comprehend easily. We can watch something that acts like an atom, at a size we could hold in our hands. MIT researchers have produced visible interference fringe patterns from sodium BECs, demonstrating quantum mechanics effects on the macroscale. That alone is worth notice.
Perhaps most interestingly, BECs have been used to slow the speed of light to a crawl—from 186,282 miles per second (3×108 m/s) in a vacuum to 38 miles per hour (17 m/s) in a sodium BEC. No other substance so far has been able to slow the speed of light within orders of magnitude of that speed. Although so far this discovery has not been applied to any technological problems, researchers at Harvard suggest that it might make possible revolutions in communications, including possibly a single-photon switch.
The Bose-Einstein Condensate is to matter as the laser is to light—the analogy is precisely that simple. It took twenty years from the invention of the laser until its technological applications began to take off. At first, lasers were considered too difficult to make to ever find use in everyday applications; now, they’re everywhere. The characteristics of BECs, specifically their response to sound and other disturbances, are still under investigation, but they hold the promise of many curious developments to come.
Marissa K. Lingen is a freelance writer living in Hayward, CA. Her background is in physics, but she’s currently also interested in Finland, early (pre-transistor) computing, and moose.
Links
The BEC Homepage.
An Introduction to BECs.
An article on atom lasers.
Sleeping with the Bug-Eyed Monster: Sexuality in the Novels of Anthony, Heinlein, and Le Guin
By Jim C. Hines
12/17/01
“The dominant … view since the eighteenth century has been that there are two stable, incommensurable, opposite sexes and that the political, economic, and cultural lives of men and women, their gender roles, are somehow based on these ‘facts.’”—Thomas Laqueur, “Of Language and the Flesh”
“The king was pregnant.”—Ursula K. Le Guin, “Is Gender Necessary? Redux”
Introduction
Traditionally, one of the goals of science fiction is to ask the question, “What if?” In the words of Ursula K. Le Guin, science fiction is a thought-experiment. It is a chance to bend the rules, and those rules can range from astrophysical laws to technological limitations to sociological norms. Given society’s fascination with all things sexual, the mores and traditions surrounding sexuality have been a common area of exploration in science fiction.
Le Guin’s essay, “Is Gender Necessary? Redux” deals with the portrayal of gender and sexuality. Sexuality is often the focus of the science fiction author’s question, “What if?” Yet the extent to which the author can explore this question is limited in a variety of ways. By deconstructing the assumptions that go into science fictional portrayals of “alternate” sexual systems, one discovers that many such systems are in fact rather traditional, and that the speculative exploration is quite limited.
In her essay, Le Guin admits this point with admirable honesty. She discusses her novel The Left Hand of Darkness, in which she attempted to portray a world without male-female identity. An admirable experiment in theory, the result falls short of its goal. After all of Le Guin’s work to create an asexual society, the characters tend to slip right back into traditional gender roles. “This is a real flaw in the book,” Le Guin admits.
But Le Guin is still a step ahead of most authors in that she recognizes and admits the difficulties in attempting to question and explore sexuality. Other authors, in the attempt to produce new and alien systems of sex and gender, instead tend to reproduce rather simplistic sexualities whose connection to traditional sex roles is quite transparent. Such is the case in Piers Anthony’s Cluster.
Finally, there are authors such as Robert A. Heinlein, who tend to leave biological sex alone and instead concentrate on sexual relationships. But once again, for every new or alternative idea Heinlein explores, there is a strong compensation in the opposite direction. A group marriage, for instance, will be counterbalanced by an exaggeration of traditional gender roles.
So in most cases, science fiction’s thought-experiments with sex have fallen short of their goals. One way or another, societal norms have a way of counteracting truly original ideas and pressing them gently but firmly back into the context of a larger, socially accepted system. In essence, science fiction’s sweeping vision of the future all too often finds itself bogged down by the past and the present.
Cluster
On the surface, Piers Anthony’s Cluster seems an excellent example of a novel that challenges traditional views of sexuality and explores alternatives. The novel tells the story of Flint, a human from one of Earth’s outmost colony worlds. Flint’s “aura” is stronger than most humans,’ which allows him to transfer into alien hosts. Throughout the book, Flint jumps from one host to another, giving the reader a chance to explore Anthony’s esoteric collection of alien species. In most cases, this exploration revolves around sex, as Flint proceeds to copulate in one way or another in nearly every alien host he inhabits. The book almost serves as a xenophilic Kama Sutra, describing sex acts practiced throughout the galaxy.