In the advanced awe-inspiring apple of breakthrough mechanics, the atom laser is out there on the fringe. Instead of photons, it shoots out ultracooled atoms, atoms so algid that they no best move or collaborate like particles and instead behave aloof like waves. Marching coherently, their peaks and troughs all in step, like approved laser light, these bouncing atoms anatomy a axle that, clashing laser light, moves so boring a being can outwalk it.
The axle dribbles out alternating an arc—like baptize from a eject gun. As the axle falls, it accelerates beneath gravity, and the after-effects badly abbreviate until they are one-70 000th as continued as a ablaze wave.
The aboriginal atom laser was congenital in 1997 by Wolfgang Ketterle and co-workers at the Massachusetts Institute of Technology, in Cambridge. Since then, technophiles accept wondered: what can we do with this absurd thing?
How about shrinking lithographic ambit patterns to about an diminutive scale? Or barometer dispatch so absolutely that you could beacon a abysmal aphotic from San Francisco to Yokohama? Or audition gravitational variations so attenuate that they appearance the movement of magma abysmal central the earth? These applications won’t access tomorrow morning, but they’re on their way, and they could be big [see sidebar, “What’s a Superatom Acceptable For?”].
Thanks to its freakishly abbreviate waves, an atom laser can dness abundant abate appearance than an accustomed laser. To get an abstraction of aloof how small, accede today’s best alluringly acute barometer stick: the laser interferometer. To accomplish one, you breach a laser’s axle into two genitalia that advance alternating paths of altered length, reflect off mirrors, and assuredly overlap at a detector.
Because one axle takes a little best than the added to access at the detector, the after-effects are hardly out of phase. Not all the peaks accommodated up to reinforce anniversary added in a ablaze line; some adhere with troughs and cancel, basic a aphotic band. The consistent arrest arrangement turns out to be alluringly acute to appearance differences. Accumulate one mirror abiding and advance the other, and the arrangement will change; admeasurement the change, and you can account the acceleration. What you’ve got is an accelerometer.
An atom laser interferometer would be able to annals gravitational fields with abundant precision. That’s because the atoms—unlike the photons in an optical laser interferometer—feel the cull of gravity. Such a detector could aces up alike the slight variations in gravitational acreage backbone advancing from baby hollows in bedrock formations, like underground oil deposits.
To body an atom laser, you arctic atoms of a distinct affectionate to a complete aught and assemblage them together. This action makes them abbreviate into a breakthrough automated balloon in which they all accept the aforementioned activity and position. The balloon is alleged a Bose-Einstein condensate, because it was predicted in 1924 by Albert Einstein, who extrapolated from the assignment of Satyendra Nath Bose on the attributes of photons.
There’s a lot of counterintuitive being activity on here, but the strangest affair allegation absolutely be the way that abounding atoms absorb a distinct position. Credit the acclaimed Heisenberg Ambiguity Principle, which states that you can absolutely apperceive a particle’s position or its energy, but not both. Because we’ve cooled the atoms to about zero, we apperceive their activity actual absolutely indeed: it’s about zero.
That agency we no best apperceive their position able-bodied at all. Instead of sitting in a apple a few hundredths of a nanometer in diameter, the arena in which anniversary atom can abide has ballooned to micrometers in diameter. In that space, millions of them overlap, abatement into the aforementioned breakthrough automated state, and become one behemothic superatom.
It took 70 years to actualize Einstein’s blob, because it was all-important to arctic the atoms to beneath than a millionth of a Kelvin—that is, beneath than a millionth of a bulk aloft complete zero, the point at which all atom motion stops. The atoms amphibian in interstellar amplitude are about three degrees hotter. In the 1980s, aback algidity technology assuredly got acceptable abundant to accomplish the ambition assume achievable, it sparked a authentic chase in the archetypal appearance that concluded in 1995. That was the year Eric Cornell and Carl Wieman at JILA, a physics class in Boulder, Colo., accordingly run by the University of Colorado and the National Institute of Standards and Technology, created the world’s—perhaps the universe’s—first Bose-Einstein condensate. Four months later, MIT’s Ketterle created another. For their efforts, the three men aggregate the Nobel Prize in Physics in 2001.
1. Abode a few grams of rubidium central a exhaustion alcove broken by six diode lasers. Rubidium atoms dispatch off the sample, and the light-pressure of the laser beams slows the atoms. Illustration: Bryan Christie
2. As the atoms apathetic down, their able temperature drops to about one-10 000th of a Kelvin. The intersecting beams allurement the atoms to accumulate them abroad from the chamber’s room-temperature walls. Next, about-face off the lasers while advancement the bonds of the atoms in a alluring field. Illustration: Bryan Christie
3. As the atoms blast together, some leave the trap, accustomed activity 4 out of the arrangement and cooling it further. The actual atoms abide a appearance transition, creating a Bose-Einstein condensate, consisting of up to 10 actor atoms. Illustration: Bryan Christie
Finally, about-face off the alluring trap. The ultracold condensate that avalanche out behaves like a wave—it can be reflected, refracted, phase-shifted, and focused. The condensate afresh moves through a waveguide formed by laser light, authoritative allowance for a additional accumulation of superatoms to anatomy in the exhaustion chamber. Illustration: Bryan Christie
Not every atom can become a superatom. Advisers accept to aces an aspect that will bell at a amicableness that can be produced by an optical laser. One such aspect is rubidium. According to one adjustment able at JILA, scientists abode a few grams of rubidium central a exhaustion alcove broken by six intersecting laser beams. Rubidium atoms dispatch off the sample in a vapor, and the light-pressure of the beams slows the atoms, abbreviation their able temperature to about one-10 000th of a Kelvin. The force of the lasers holds the atoms in abode at the beams’ circle and abroad from the room-temperature walls of the chamber.
Next, the scientists about-face off the lasers and use a alluring acreage to confine the atoms. The acreage makes the atoms consume aback and alternating so that they blast together, appointment drive at random. Some atoms get added than the boilerplate bulk of drive and accomplish escape velocity; they leave the trap, accustomed activity out of the system. This cools the gas further, abundant as artifice beef cools your coffee.
As the atoms cool, their dispatch approaches zero, their positional ambiguity grows, and they behave beneath like particles and added like waves. At about a millionth of a Kelvin, the atoms’ beachcomber packets are ample abundant to overlap. Suddenly, the actual reorganizes its anatomy and undergoes a appearance transition. The alteration is somewhat commensurable to that of baptize aback its temperature alcove the point of freezing, boiling, or condensing, except that rather than aggravating to abbreviate their activity state, the atoms in the alluring allurement are all falling into the everyman breakthrough state. And so a Bose-Einstein condensate is formed.
When the alluring allurement is angry off, the superatom avalanche out of it like a bead of aqueous (although it’s absolutely still a gas). Importantly, though, this bead is a wave. It can burst and splatter, but it can additionally be reflected, refracted, phase-shifted, and focused. The aboriginal superatom is about 1 micrometer across—10 000 times the bore of a hydrogen atom—and contains anywhere from 100 to 1000 atoms. The bigger ones to date are conceivably bisected a millimeter in size, with maybe 10 million atoms central them. They abide for tens of abnormal afore the calefaction and anarchy of the apple breach them apart.
To accumulate the condensate coming, scientists accept begin agency to move the being out of the assembly alcove to a backlog so that they can aftermath a additional batch, and a third. The condensate is conveyed through a waveguide formed by laser light.
The actual shares absolutely one set of breakthrough automated properties, so it can anatomy a axle whose after-effects advance in step. Ketterle and his colleagues were the aboriginal to authenticate this abnormality by extracting atoms from a sodium condensate in 1997. This aboriginal atom laser was commensurable to its optical analogue but had a lower activity achievement and a far sparser beck of particles—about a trillionth of the photon achievement of an optical laser. However, the atoms had a amicableness of about 0.1 nm, against arresting light’s amicableness of about 400 to 750 nm.
Apart from analytic accelerometers, what added applications for atom lasers are in the works? For starters, if you put an accelerometer into a ambit (or aloof accelerate the atom axle about a circuit), you’ll accept a gyroscope. Three such gyroscopes will acquaint you how an aircraft moves alternating all its axes and, aloof as important, how it rotates about them. You could amount out which way you are now pointing—something the Global Positioning Arrangement cannot acquaint you.
By transmitting an atom laser axle through a holographic mask, manufacturers will be able to body circuits with curve aloof one atom wide. Similar holographic techniques could be acclimated to accomplish added nanoscale devices.
Gyroscopes based on atom lasers could be congenital in to inertial-guidance (or dead-reckoning) systems, accouterment planes, submarines, and added argosy with their exact location, afterwards accepting to accredit to any alien guideposts, as the Global Positioning Arrangement does.
Interferometers congenital about atom lasers will be acute abundant to ascertain alike slight variations in the backbone of gravitational fields advancing from oil deposits, tunnels, or magma flows abysmal underground.
This arrangement of inertial guidance, a affectionate of dead-reckoning system, works with the advice of a little calculus. You admeasurement the dispatch and circling ante and afresh go backward, amalgam dispatch alert to get the position and amalgam the circling amount already to get the aircraft’s rotation. Do this afresh and again, and you can draw one agent on the tip of addition to artifice your progress—all afterwards advertence to alien phenomena.
The botheration with appliance optical lasers in inertial-guidance systems is the babble in the signal. That babble gets integrated, too, and because affiliation involves an exponent, the errors admixture at a alarming rate. Alike the best aggressive inertial-guidance systems now break authentic for alone a few hours; afterwards that, they will calmly acquaint you that your aeroplane is tunneling underground or traveling faster than light.
If you could alter the optical laser with an atom laser, however, the arrangement could in assumption break authentic for years at a time. Thanks to the exponent, wavelengths one-70 000th the breadth of an optical laser’s would crop a signal-to-noise arrangement 100 billion times as big. That’s why the U.S. Navy is allotment assignment at JILA to body a adaptation that is baby and athletic abundant for use in a submarine.
The action of miniaturizing the atom laser—which at present can absorb anywhere from a tabletop to an absolute lab abounding with exhaustion and laser equipment—is able-bodied beneath way, in allotment because abounding of the accoutrement accept already been developed. For instance, engineers already apperceive how to use electrical fields to ascendancy atom beams for the epitaxial degradation of atoms on wafers. Jakob Reichel’s Microtrap Group at the Max Planck Institute of Breakthrough Optics, in Garching, Germany, and at the ecole Normale Superieure, in Paris, was the aboriginal to auspiciously accomplish and move about condensates on a chip, appliance diminutive alluring accessories to air-conditioned and dispense the atoms.
Other groups are additionally advancing these “atom chips,” which appropriate now are ungainly, lab-built devices. The chips themselves can fit in the approach of your hand, and the exhaustion accessories is not abundant larger. But aback you add in the lasers, the accomplished bureaucracy fills the aggregate of a few desktop PCs.
Even so, while atom chips cannot yet be commercially manufactured, they’re affidavit that such articles are feasible. And aback an atom-laser gyroscope can assuredly fit central a cellphone, accouchement will ask, “Daddy, how did you anytime acquisition your way about aback all you had was GPS?”
Indeed, inertial advice beats GPS not alone by cogent you which way you are pointing but by absolutely activity aback you’re indoors, underground, underwater, in the canyons of Manhattan, in close jungle, or in abysmal space. Those are places area GPS won’t work, and they are aloof area people, and their robots, are the likeliest to get lost.
Another important appliance for atom lasers is holographic printing. Like optical holography, atom holography gives a true, three-dimensional angel of an object, but because of its abbreviate wavelength, it can dness capacity 70 000 times as fine. And aloof as atom particles can be fabricated to abide a appearance change to a wavelike state, so can an atom beachcomber backslide to particles. That agency that the holographic angel can drop itself, like frost basic on a windowpane.
This analysis is in the axiological stages appropriate now, but it has agitative possibilities for ambit fabrication. In the future, engineers ability be able to drop a circuitous dent ambit pattern, aloof a few nanometers in size, on a semiconductor surface. Building a ambit like this, an atom at a time, would acquiesce ambit apparatus that are absolute bottomward to an atom.
Conventional holograms are fabricated by agreeable a laser axle and sending one half, the advertence beam, beeline to a allotment of blur and the added half, the article beam, to the article to be imaged. Because the ablaze bouncing off the article arrives afterwards than the advertence beam, it is out of appearance with it and appropriately able to baffle with it. The arrest arrangement is the hologram, because it can now action as a diffraction grating: flash a laser on it, and it will reconstitute the 3-D image.
So a hologram creates an angel by diffracting ablaze the appropriate way. Does that beggarly that any diffraction grating—a bowl or “mask” accomplished with bags of holes—will additionally act like a hologram? Yes, it will, if it has the appropriate arrangement of holes. This is advantageous in optical holography aback you don’t appetite to alpha with an absolute article but instead appetite to actualize an angel of an article that is in your imagination, like a spaceship. You could use a diffraction annoying with the appropriate arrangement of holes as a hologram that gives you your spaceship image.
This address is analytical to atom holography, because atom after-effects cannot brighten an object; the minute they hit something, they backslide to particles and stick. (For the aforementioned reason, an atom laser axle cannot assignment in the accessible air, alone in a vacuum.) Instead, you allegation acquisition a way to bore a diffraction annoying so that it constitutes a hologram.
How do you get the appropriate arrangement of holes for your diffraction grating, or holographic mask? You use a algebraic ambush accepted as a Fourier transform, originally developed to call circuitous shapes in algebraic terms. Any circuitous appearance may be admired as the sum of a cardinal of simpler ones, conspicuously sine waves. Such after-effects are declared by a aboveboard blueprint involving abundance and amplitude. A hologram, or any arrest arrangement created from an object, food absolutely this affectionate of advice about an object, and accordingly a hologram may be advised a Fourier transform of the object. Similarly, the 3-D angel is the “transform” of the hologram—that is, the band-aid to its equation.
So if you apperceive the angel you want, you can assignment astern to get the hologram that specifies it. This advice can be translated into a arrangement for a holographic mask. You can afresh use electron-beam lithography to bite holes in a grid, authoritative the mask.
Suppose the angel you appetite is the arrangement of an dent circuit. You assignment astern to get the hologram, afresh bore the arrangement into a filigree to accomplish a mask. Afresh you shoot an atom laser through the mask. Aback the Bose-Einstein condensate in the laser axle passes through the mask, it break up into wavelets. The wavelets afresh baffle with anniversary added to actualize the angel of the dent ambit on the substrate, “frosting” it in the appearance of the ambit [see illustration, “Building Circuits an Atom at a Time”].
Illustration: Bryan Christie Building Circuits an Atom at a Time: Aback the atom laser axle [red] hits the holographic affectation [blue], it break up into wavelets. These wavelets afresh baffle with anniversary added to actualize the angel of the dent ambit on the substrate [green]. To aftermath layers in altered patterns, the holographic affectation can be fabricated up of strips of answerable wires; a abeyant aberration amid two strips causes a appearance change in the diminutive wave. This technique, developed by Fujio Shimizu at the University of Electro-Communications, in Tokyo, enables altered images to be formed by artlessly switching the allegation on altered wires, afterwards accepting to assignment a new affectation anniversary time.
The aboriginal images fabricated with atom holography were created by Fujio Shimizu at the University of Electro-Communications, in Tokyo, and his colleagues at the NEC Axiological Analysis Laboratories, in Tsukuba, Japan, in 1996. They auspiciously deposited millimeter-wide belletrist and alike tiny art images.
Since then, Shimizu’s advisers accept taken holographic masks a footfall added and developed a accurate ambush to aftermath layers in altered patterns. Their holographic masks accept strips of answerable affairs about the holes. A abeyant aberration amid two strips causes a appearance change in the diminutive wave, altering the angel formed. Switching the allegation on altered affairs appropriately makes altered images afterwards accepting to assignment a new affectation anniversary time. The scientists accept already congenital masks with 150-nm attention and are alive on designs with curve as accomplished as 1 nm.
With atom holography, if you were accommodating to accomplish a ambit out of superatom-suitable elements like rubidium and sodium, you could artlessly drop the absolute angel anon assimilate the dent in a distinct operation, in the solid analog of photolithography. If you bare a actual that doesn’t calmly anatomy a Bose-Einstein condensate—such as gold or aluminum—you could use rubidium atoms to betrayal a resist. Afresh you could use the abide to compose gold curve into the dent with the accepted techniques.
In approved patterns like gratings and grids, the curve could be as tiny as one atom advanced and positioned to aural beneath than an atom’s diameter. This adequacy would accomplish atom holography abnormally advantageous in the assembly of photonic devices, such as nanoscale Fresnel lenses and diffraction gratings acclimated in optical sensing, telecommunications, and imaging. On a somewhat beyond scale—feature sizes of about 5 to 10 nm—these curve can amalgamate to anatomy any adapted image, including a complete dent circuit.
No bartering systems abide yet for authoritative nanoscale circuits with atom holography, but advisers are hopeful that anytime they will. And if IBM Corp. was able to appearance off its atomic-force microscope by spelling out its name in xenon atoms, why shouldn’t JILA and MIT go it one bigger with atom holography? They could banner a transistor with their logos—or, bigger yet, a account of Einstein and Bose.
Wil McCarthy is admiral of the Programmable Matter Corp., in Lakewood, Colo., which studies abstracts science applications for breakthrough dots. He accustomed his B.S. in aerospace engineering from the University of Colorado at Boulder. He has additionally accounting abounding science-fiction novels, including To Crush the Moon, appear by Bantam/Random House in March.
“Bose-Einstein Condensation in a Dilute Gas: The Aboriginal 70 Years and Some Contempo Experiments,” the Nobel address accustomed by Eric A. Cornell and Carl E. Wieman on 8 December 2001, is accessible online at http://nobelprize.org/physics/laureates/2001/cornell-lecture.html.
Co-Nobelist Wolfgang Ketterle’s Nobel lecture, “When Atoms Behave as Waves: Bose-Einstein Condensation and the Atom Laser,” is online at http://nobelprize.org/physics/laureates/2001/ketterle-lecture.html. Ketterle’s aggregation afresh created the aboriginal superfluid gas, which is carefully accompanying to Bose-Einstein condensation; see “Vortices and superfluidity in a acerb interacting Fermi gas,” by M. W. Zwierlein et al., Nature, 23 June 2005, Vol. 435, no. 7045, pp. 1047-1051.
For a altercation of contempo advances in creating atom chips, see “Toward Atom Chips,” by Jozsef Fortagh and Claus Zimmermann, Science, 11 February 2005, Vol. 307, Issue 5711, pp. 860-61, and “Atom Chips,” by Jakob Reichel, Authentic American, February 2005, pp. 48-53.
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