Ultracold atoms: new gravity yardstick?
The laboratory feat of laser-cooling atoms to near absolute zero is verging on its first commercial application.
A prototype of a novel, laser-cooled device for measuring gravity, described in the Aug. 3 Physical Review Letters Physical Review Letters is one of the most prestigious journals in physics. Since 1958, it has been published by the American Physical Society as an outgrowth of The Physical Review. , promises to be a boon for oil exploration, geophysical measurements, and military uses, says Mark A. Kasevich, the Yale University Yale University, at New Haven, Conn.; coeducational. Chartered as a collegiate school for men in 1701 largely as a result of the efforts of James Pierpont, it opened at Killingworth (now Clinton) in 1702, moved (1707) to Saybrook (now Old Saybrook), and in 1716 was physicist leading the U.S. Navy-funded development team. "I think there's a possibility for a basic science idea to have an impact technologically," he says.
Nobel prize-winning techniques developed in the 1980s to slow, and thus cool, atoms by zapping them with laser-generated photons have led to stunning advances in physics Advances in Physics, published by Taylor & Francis, is a leading physics journal that focuses on review articles in condensed matter physics. Advances in Physics is consistently ranked as most influential condensed matter physics journal (impact factor 2004, ISI: 15. , including the creation of Bose-Einstein condensates, which are ultracold clusters of atoms sharing one quantum state quantum state
Any of the possible states of a system described by quantum theory.
A description in quantum mechanics of a physical system or part of a physical system. (SN: 7/25/98, p. 54). The only practical gadget to emerge from the field, however, has been a better atomic clock atomic clock, electric or electronic timekeeping device that is controlled by atomic or molecular oscillations. A timekeeping device must contain or be connected to some apparatus that oscillates at a uniform rate to control the rate of movement of its hands or the , attractive only to a few time-standard labs, says Steven L. Rolston at the National Institute of Standards and Technology National Institute of Standards and Technology, governmental agency within the U.S. Dept. of Commerce with the mission of "working with industry to develop and apply technology, measurements, and standards" in the national interest. in Gaithersburg, Md.
The newer instrument determines gravity's gradient, or change in strength with position, by comparing the gravitational acceleration In physics, gravitational acceleration is the acceleration of an object caused by the force of gravity from another object. An interesting fact is that any object will accelerate towards a large object at the same rate, regardless of the mass of the object. of two clouds, each made up of millions of cesium cesium (sē`zēəm) [Lat.,=bluish gray], a metallic chemical element; symbol Cs; at. no. 55; at. wt. 132.9054; m.p. 28.4°C;; b.p. 669.3°C;; sp. gr. 1.873 at 20°C;; valence +1. atoms. The clouds are cooled to 3 microkelvins and spaced a meter apart. Observing interference within each cloud's quantum-mechanical wave behavior yields a precise measurement of gravity at that position.
"It's beautiful work," Rolston says. "It's nice to see something showing some true practicality."
Measurement of gravity-gradient changes over an area can reveal subsurface irregularities in mass, which may represent underwater mountains or subterranean oil deposits. The Navy already uses precision-machined electromechanical The use of electricity to run moving parts. Disk drives, printers and motors are examples. Electromechanical systems must be designed for the eventual deterioration of moving components that wear over time. The first TVs were electromechanical systems (see video/TV history). gravity gradiometers to help submarines navigate without noisy sonar. In recent years, it has made the once-classified instruments available to civilian geologists.
The quantum-mechanical gradiometer has yet to surpass electromechanical instruments in sensitivity. Its advantage lies in its remarkable stability, derived from using fundamental properties of atoms and fixed laser frequencies as references, Kasevich says. In contrast, electromechanical gradiometers require periodic calibration because their components are vulnerable to temperature change and other influences.
Gravity surveyors would welcome an instrument whose measurements didn't drift, says Richard O. Hansen of Pearson, deRidder and Johnson, a geophysics consulting company in Lakewood, Colo. The quantum-mechanical design is "gorgeous," he says, but he cautions that a field-deployable version must maintain its laboratory performance while remaining small, light, and inexpensive.
Ultimately, the quantum-mechanical gradiometer should achieve a 10-fold to 100-fold edge in sensitivity over electromechanical versions, Kasevich says. On the other hand, he acknowledges that it has so far passed only a "proof of principle" test, with its first field trials anticipated within a year.