Stopping Atoms (Extremely) Cold
Researchers develop first all-optical technique to produce Bose-Einstein condensates.
Georgia Institute of Technology physicists have demonstrated the first all-optical technique for producing Bose-Einstein condensates, a form of matter in which atom cooled to a fraction of a degree above absolute zero stop their normal motion – and enter a single quantum state in which all atoms behave identically.
Georgia Institute of Technology researchers Michael Chapman and Murray Barrett adjust the optics of lasers used to cool and confine Bose-Einstein condensates in their lab.
Operating inside a vacuum chamber, the technique uses powerful carbon dioxide lasers to confine gaseous rubidium-87 atoms and produce the final cooling step needed to form the condensate.
The Georgia Tech method is simpler, faster and more flexible than the magnetic confinement technique used to produce the condensates since 1995. Dispensing with magnetic confinement should allow the new technique to be used on a wider variety of atoms, atomic mixtures and even molecules.
"This is the first time we've been able to make a condensate using a completely different technique," explained Michael Chapman, an assistant professor in the Georgia Tech School of Physics. "The simplicity of the technique and its speed are somewhat remarkable given that people have been trying to get all-optical Bose-Einstein condensation for so long."
Chapman and colleagues Murray Barrett and Jacob Sauer describe their work in the July 2 issue of Physical Review Letters.
Physicists create Bose-Einstein condensates through a multi-step process that uses both magnetic and optical techniques to confine and cool the gaseous atoms. First, a magneto-optical trap is used to confine the cloud of atoms. In a technique known as Doppler cooling, carefully-tuned lasers then remove energy from the atoms, dropping their temperature to a few millionths of a degree above absolute zero (-273.15 Celsius).
The final step uses evaporative cooling to remove the hottest atoms from the top of the confinement, dropping the temperature of the atom cloud to 100 billionths of a degree above absolute zero – cold enough to form the condensate.
In the technique used since 1995, powerful magnetic fields confine -- or "trap" -- the cloud of atoms during evaporative cooling. Applying a field of radio frequency energy causes the most energetic – and hottest – atoms to be ejected from the confined cloud, producing the final temperature drop needed produce condensation.
The Georgia Tech process relies on an all-optical technique – two crossed laser beams – to confine the cloud of atoms during evaporative cooling. To bring about the final cooling step, researchers rapidly reduce the laser power, lowering the depth of the confinement. That forces the hottest atoms to evaporate, forming the Bose-Einstein condensate in just two seconds – several times faster than the magnetic process.
Physicists have attempted to produce condensates through optical means for years. Chapman doesn't yet know why his team succeeded where others failed, but he speculates that the carbon dioxide lasers or the rubidium-87 isotope may have provided an edge. Carbon dioxide lasers can be precisely controlled to avoid transferring energy to the atom cloud, and the rubidium-87 isotope has properties more favorable than the rubidium-85 studied by other researchers.
Absorptive image of Bose-Einstein condensate atomic cloud showing three distinct components.
Because it relies on interaction with the magnetic dipole of atoms, magnetic confinement techniques work only with certain atoms in some of their energy states. That limits the elements from which physicists can make Bose-Einstein condensates.
The Georgia Tech optical technique has no such restriction, allowing physicists to use any atom that can be sufficiently cooled, including alkali rare earth elements such as magnesium and strontium. It could even produce condensates from atomic mixtures and molecules.
"That's quite exciting from a physics standpoint, because it is a whole new aspect of Bose-Einstein condensation that wasn't considered by Bose or Einstein," Chapman said. "Our technique is amenable to trapping a mixture of atoms, which opens up the possibility of condensing two different species of atoms at the same time."
Other advantages: the optical technique uses less sophisticated traps, lower vacuum levels – and doesn't need bulky, power-hungry magnetic coils.
Chapman and his team have produced condensates containing up to 35,000 atoms, far less than the millions of atoms captured by magnetic means. But Chapman sees no fundamental reason why the optical process can't be scaled up to match those numbers.
Though potential applications remain far in the future, the Bose-Einstein phenomenon has attracted intense interest because it could do for atoms what lasers have done for photons. Lasers produce streams of photons with identical wavelengths and energy levels, all moving in the same direction. This coherence powers a broad range of applications from high-speed communications to metal cutting.
"A lot of the excitement about atomic Bose-Einstein condensates is that this sort of coherence – getting all the atoms to be in one state and do everything at the same time – could eventually lead to some interesting developments," Chapman noted. "Where this will lead is hard to predict, but historically whenever we've been able to get more control over physical systems, that has led to dramatic new directions in science and technology."
Atomic lithography, coherent matter wave optics and coherent atomic interferometry are among the applications proposed.
Chapman and his team began studying Bose-Einstein condensation because of their interest in controlling atoms for investigating quantum entanglements, which have applications for quantum logic – a potential new area of computing. To accomplish quantum computing, however, scientists will have to control thousands of atoms individually.
The phenomenon is named after Albert Einstein and Satyendra Bose, who proposed its possibility in the 1920s.
An image produced by the research team is the first figure to be published on the newly-redesigned cover of Physical Review Letters, which is published by the American Physical Society.
Chapman's research was supported by the U.S. National Security Agency, the U.S. Army Research Office and the Advanced Research and Development Activity (ARDA).
A new study of the Earth's mantle beneath the ocean near Iceland provides the most convincing evidence yet that simple buoyancy of hot, partially molten rocks can play an important role in causing them to rise and erupt through the surface at mid-ocean ridges.
Bathymetric map of the North Atlantic region included in a study showing that buoyancy plays an important role in causing partially molten rocks to rise and erupt through the surface at mid-ocean ridges. Surface waves of earthquakes (open circles) from the Reykjanes Ridge (RR) and the Gibbs Fracture Zone (GFZ) were recorded on Iceland at the sites indicated by the triangles.
Published August 31 in the journal Science, the Georgia Institute of Technology study also shows that heat from a volcanic hotspot in Iceland can affect normal mantle convection activities at a nearby ridge.
The motion of the Earth's surface plates is driven by a convection cycle in which cold material sinks into the deep mantle and hot material rises toward the surface. At most mid-ocean ridges, scientists believe that hot rock rises passively to fill the gap created by the separation – or spreading – of the plates.
But a detailed analysis of seismic waves passing through regions of upwelling rock provides new evidence that another mechanism – buoyancy much like that of a hot-air balloon – helps drive partially melted rocks from the Earth's mantle up to the surface at these ridges. The effect is especially pronounced at the Reykjanes Ridge, a portion of the mid-Atlantic ridge that gains significant heating from Iceland's volcanic hotspot. This additional heating adds 30 to 80 degrees Kelvin to the mantle temperature there and may play an important role in powering the buoyancy at this location.
"These observations imply that the volcanic rocks erupting on the surface forced their way through the upper 60-100 kilometers of the Earth through the power of their own buoyancy," said James B. Gaherty, author of the paper and an assistant professor in Georgia Tech's School of Earth & Atmospheric Sciences. "You can envision this like a hot-air balloon that bursts through its hangar roof rather than waiting for the rooftop door to open. This contrasts with most spreading centers, in which the hot rocks reach the surface simply to fill the void left by the spreading plates."
Gaherty studied seismic waves from 17 earthquakes as they passed through the Reykjanes Ridge. Waves with vertical polarizations passed through the region at the speed expected. However, transversely polarized waves were delayed, providing Gaherty information about how the orientation of crystalline structures in the region may have been deformed by the mantle flow.
"The propagation speed of these waves provides information about two critical Earth parameters: the relative temperature of the rocks beneath the ridge and the crystalline structure or fabric embedded in the rocks as they have deformed during convection," he explained. "In this case the fabric is consistent with buoyancy-driven upwelling of the partially melted rock."
Because the ridge is adjacent to a volcanic hotspot on Iceland, the study also provides new information on how such heat sources affect ridges – and may prompt reconsideration of existing models that explain such sea-floor spreading. For example, Gaherty found that heating from the Iceland hot spot extended to a depth of at least 100 kilometers.
Though Gaherty's study was confined to the Reykjanes Ridge, he believes buoyancy may also play a role in ridge dynamics for other areas.
"It provides unique observational evidence that buoyancy-driven upwelling is an important component of ridge dynamics, especially in environments where passive sea-floor spreading is too slow to accommodate melt production," he writes. "The presence of anomalous mantle fabric to about 100-kilometer depth implies that the hotspot modulates upper-mantle dynamics beneath the ridge to at least this depth."
Earth scientists have previously discussed buoyancy as a mechanism for powering volcanic upwelling, but direct evidence for it had been limited. "This paper provides some of the most direct evidence to date," Gaherty said.
The study also provides additional information about the thermal anomaly associated with the Iceland mantle plume, which has been the topic of significant study. Further, it provides more evidence that slow-spreading ridge structures in the Atlantic differ in important ways from comparable but faster-spreading structures in the Pacific.
Gaherty's work focuses on understanding the connection between solid-state convection in the Earth's mantle – a solid rock region extending from 30 to 3,000 kilometers in depth – and surface deformation and plate tectonics.
Hot upwelling of volcanic rock from the mantle typically occurs in two environments: (1) mid-ocean ridges, which are linear chains of volcanic activity along the boundary where two plates move away from one another, and (2) "hotspots," which are point sources of high volcanic output associated with quasi-stationary and long-lived heat sources in the mantle. The mid-Atlantic ridge is an example of the former; Hawaii, Iceland and Yellowstone National Park are examples of the latter.
The research was sponsored by the National Science Foundation.
In Chemical Engineering 4600 at the Georgia Institute of Technology, chemical formulas, thermodynamic equations and process flow diagrams take a back seat to invention disclosures and congressional position papers.
Georgia State Senator Mike Polak talks about the legislative process with students from Chemical Engineering 4600. The class session was held in the historic Georgia State Senate chambers.
For an entire semester, Mark Prausnitz helps his engineering students analyze audiences and study how a broad range of communication tools can help them reach their real-world goals. He makes that point through a case study of a real product – and a series of weekly guest speakers that include state senators, graphic communicators, lobbyists, company CEOs, patent attorneys, regulators and others who may help determine the product's ultimate success.
"Communications is really important to the success of a professional engineer," explains Prausnitz, an associate professor in Georgia Tech's School of Chemical Engineering. "The world of a professional engineer intersects with law, business, politics, ethics and all the different pieces of the modern world. There is a lot more to it than the narrow scope of things students tend to encounter in a typical college class."
To prepare them for leadership roles in engineering, business and society, he helps students develop the communication skills they'll need in a broad range of areas: influencing legislation and the political process, pushing new products through patenting and marketing, persuading management to try new approaches and explaining complex issues to non-technical audiences.
Funded in part by the National Science Foundation, the course focuses on the many steps involved in developing and preparing for market a real product – a nicotine patch – produced by a hypothetical company. Through this case study, students learn that getting a product to market takes more than good engineering. Prausnitz likes the case study approach because it unifies the communications topics and "provides something tangible that the students can grab onto."
The course was offered for the fourth time during Spring Semester 2001. It has been co-taught at different times by Melissa Bradley and Elizabeth Bolton, who further broaden the scope of the course through their liberal arts backgrounds and experience teaching communications at Georgia Tech.
Beyond learning the basics of communications, Prausnitz wants his students to deal with questions whose answers aren't black-and-white. Engineers accustomed to finding the single precise answer to an equation often become frustrated in the gray areas of communication, Prausnitz notes, so he purposely makes assignments open-ended to show students that there can be many solutions to a problem.
In one assignment, for example, students address quality issues in a memo to factory personnel. "You want to convince the factory workers to be more careful in the procedures they are following because the final product has defects," Prausnitz explained. "How to do that is up to you. What tone do you take? Do you chastise the workers? Are you supportive? How do you approach the problem? There isn't one single solution."
To emphasize that, the students spend the first part of each class period critiquing each other's work. That exposes class members to divergent approaches and demonstrates that there are many workable solutions. Though the course digs into many issues, Prausnitz believes the single most important lesson for his engineering communicators is: "know your audience." From that knowledge, he and his guest speakers encourage students to set goals and choose the best communication tools to reach them.
"The way you write something in a scientific journal is different from the way you write a press release," he noted. "The way you present something to a community organization is different from how you present to the company's board of directors. We address a lot of different audiences and a variety of different goals."
Though many universities offer writing clinics to help their students with papers and teach them how to communicate with colleagues, Prausnitz believes his course is unusual in addressing communications so broadly.
"During their careers, engineers may need to work with a graphic designer or be drawn into the political process," he said. "Most engineers have not been prepared for these types of interactions and often cannot communicate effectively."
David Bonnichsen is a believer. Now a process engineer with Solvay Polymers in Houston, the Georgia Tech graduate enrolled in the course to improve his writing and speaking skills. He believes the course is one of the most important he took at Georgia Tech.
"Each day I speak with a variety of different people, from plant operators to corporate vice presidents," he said. "It is imperative that I understand the needs of the audience before I can effectively communicate with them. My ability to communicate effectively is a result of a personal desire to be a better communicator, and the teaching and coaching I received in the course."
Companies need smart engineers to develop the ideas of the future, but without communications skills, Bonnichsen says many good ideas never reach fruition.
"Communications skills are single-handedly the most important asset an individual can possess," he added. "Companies want smart individuals working for them…but companies want to know that their employees can communicate an idea in such a way that they can get 'buy-in' from everyone. Mark's class takes that idea from the mind to the paper to the people."
At career fairs, Zubair Anwar heard company recruiters emphasize the importance of communication skills. He enrolled in the course to get them, and believes an awareness of audience needs and ability to make verbal presentations were the most important skills he learned.
"While there was a lot of writing involved throughout the course, audience analysis and oral skills were emphasized the most," he said. "I feel the course may give me an advantage over my classmates when we walk into the real working environment."
Though few of his students probably realize it, Prausnitz is uniquely qualified to teach a course in communications for engineers. Over the past 15 years, he has taught public speaking at three different universities. For two years starting in the spring of 1998, he was deluged with media inquiries about a microneedle array he developed with another Georgia Tech professor, Mark Allen. He helped turn that invention in a company that gained financing, grew and was sold.
Prausnitz has also been involved in more than a dozen patents, served as an expert witness twice, consulted with numerous companies and published almost 50 scientific papers. Those experiences underline the importance of what the class teaches, and provide realistic scenarios for study.
"This class is about interacting with the big world that too many engineers do not realize they can influence, and even more importantly, do not realize influences them," he said. "We are trying to give students some of the information needed to become engineering, business and societal leaders."
New research into the activity of a key "motor" protein suggests that a unique form of random motion powered by thermal energy may play a vital role in moving enzymes and other chemicals inside cells. Beyond providing a better understanding of sub-cellular functions, the National Science Foundation-sponsored work may offer a new mechanism for generating motion in future nanometer-scale machines.
New research into the activity of a key "motor" protein suggests that a unique form of random motion powered by thermal energy may play a vital role in moving enzymes and other chemicals inside cells. Physicist Ronald Fox published a paper on the work in the May issue of the journal Physical Review E.
Within the cells of the body, kinesin proteins work like "cellular tow trucks" to pull tiny sacks of chemicals along pathways known as microtubules. The accepted explanation for this motion is that the kinesins use their two leg-like "heads" to walk along the microtubule paths in a deliberate way, fueled by the energy molecule adenosine triphosphate (ATP).
But in a paper published in the May 2001 issue of Physical Review E, Georgia Institute of Technology physicist Ronald Fox argues that what appears to be a walk along the microtubule is really random motion cleverly constrained by chemical switching carried out by ATP.
"These are certainly not motors in the sense of burning a fuel and having a concerted effort in a one-directional way," said Fox. "If you could see them, their walk would appear to be more like a drunken sailor than a concerted motion."
Composed of fibrous proteins, the microtubules include sites approximately 8 nanometers apart where kinesin heads can bind chemically. To move along this pathway, Fox argues that the kinesins use "rectified Brownian motion" in the following steps:
"Normally, Brownian motion cannot do anything concerted or with directionality, because it is random," Fox explained. "But what happens here is a random process in a system that has asymmetric boundary conditions created by the ATP switching. That makes it possible to get a net directed motion along the microtubule."
Structure of kinesin attached to a microtubule. A piece of the neck and both heads are shown. The neck is a coiled coil and terminates in two neck linkers, one for each head. The neck linkers are depicted as light gray segments attached to the globular heads. The microtubule is shown as a single protofilament.
The model described by Fox and post-doctoral colleague Mee Hyang Choi depends on two unique properties of structures at the nanometer-scale: thermal energy can be a robust source of power, and random motion occurs very rapidly.
"Normally, we would think of Brownian motion – or diffusion – as a very slow process," he noted. "But when you are on the nanometer scale, Brownian motion is a very rapid way to do things. Even though it is random, it allows you to explore all the possibilities very rapidly."
Using optical tweezers and other sophisticated techniques, biologists have studied the activity of kinesins, measuring their speed, pulling power and use of ATP. For instance, they can move at velocities of up to 1,000 nanometers a second, and exert forces of as much as 6 piconewtons.
Richard Fishel, professor of microbiology and immunology at the Kimmel Cancer Center in Philadelphia, Pa., studies how DNA repair genes locate and bind with damaged DNA. He believes all nucleotide-dependent processes really involve a switching mechanism, and says Fox's model explains how that works for a broad range of systems in the context of thermally powered Brownian motion.
"Ron Fox has now set the clear physical dimensions for how that has to work, and how it has to work is by rectified Brownian motion," he said. "The rectification of those Brownian events is done by the small molecule exchange of ATP for ADP. The energy that drives that process is what's important."
The switching operation that involves acceptance or removal of a phosphate controls a protein's affinity for binding to other proteins it encounters as Brownian motion moves it through cells. "What Ron has provided here is the physical reasoning behind how these collisions can work and the conformational transitions that are rectified," he explained.
The role of Brownian motion in cellular activity has been discussed before, but new experimental results and high-level mathematics in Fox's model provide the strongest evidence yet to support it. Though the experimental results are consistent with the model of rectified Brownian motion, Fox admits there is no indisputable evidence supporting his model over the accepted "power stroke" theory.
"What we really need now is an experiment that will clearly be consistent with one of these mechanisms and not the other," he noted. "That's our objective for the immediate future."
Fishel argues that a paper published May 24 in the journal Nature by researchers at the University of Tokyo and the University of California supports Fox's model of ATP switching.
Beyond the biological implications, Fox hopes the paper leads nanotechnology researchers to think about heat and motion in a new way.
"There are lessons here for nanotechnology in these biological nano-systems," he added. "This will help people to appreciate that thermal motion can actually be harnessed to do many kinds of useful work."
And the work may also restore the original hypothesis of Robert Brown, who first observed the phenomena bearing his name in pollen particles moving through water. Brown first believed that what we saw through his primitive microscope was "the secret of life." But after observing the same kind of motion with inorganic particles, he discarded that belief with disappointment.
"We're arguing that Brown really had discovered the secret of life," said Fox. "When you get into this sub-cellular level on the nanometer scale, the dynamics and vitality of protein molecules is really due to thermal motion."
Michael Amitay, a research engineer in the Georgia Tech Research Institute (GTRI) received the American Institute of Aeronautics and Astronautics Best Paper Award for "Aerodynamic Flow Control Using Synthetic Jets" with co-authors A.M. Honohan and A. Glezer. Amitay also won the 2000 Moody Award from the American Society of Mechanical Engineers for the best paper dealing with a topic useful in mechanical engineering practice.
Dale Blair, a principal research engineer in GTRI, was named 2001 Young Engineer of the Year by the Institute of Electrical and Electronics Engineers Aerospace and Electronic Systems Society.
Ronald A. Bohlander, a principal research scientist at GTRI, was elected to the Society of Manufacturing Engineers' College of Fellows. He was honored for leadership in promoting collaboration between universities and industry, and for expanding the role of university-based research and development in manufacturing and new product realization.
Robert J. Butera Jr., an assistant professor in the School of Electrical and Computer Engineering, received a James S. McDonnell Foundation 21st Century Scientist Award "for hybrid complex systems-a case study using neuronal dynamics."
W. Russell Callen Jr., a professor in the School of Electrical and Computer Engineering, received the El Paso Energy Award for Faculty Achievement "for exceptional dedication as an educator and mentor."
Jim Coleman, a senior research scientist in GTRI, won the Leadership Award from the Armed Forces Communications and Electronics Association International.
Jeffrey A. Davis, an assistant professor in the School of Electrical and Computer Engineering, received a National Science Foundation (NSF) CAREER Award "for interconnect dominant ULSI (ultra large-scale integrated) designs: a new paradigm for 21st century IC design and education."
Faramarz Fekri, an assistant professor in the School of Electrical and Computer Engineering, received a NSF CAREER Award "for finite-field wavelets for cryptography and error control coding." A first-year assistant professor, Fekri also received the Sigma Xi Outstanding Doctoral Thesis Award for his dissertation titled "Finite-field Wavelet Transforms and Their Application to Error Control Coding."
Thomas K. Gaylord, the Julius Brown Chair and Regents' Professor in the School of Electrical and Computer Engineering, received the honorary "Professional Degree in Physics" from the University of Missouri-Rolla in May 2001. Gaylord is an alumnus of the University, where he received a bachelor's degree in physics and a master's degree in electrical engineering.
Jiri Janata, the Georgia Research Alliance Eminent Scholar in Sensors and Instrumentation in the School of Chemistry and Biochemistry, was elected an honorary foreign member of the "Learned Society of the Czech Republic" for his contributions to the fields of environmental analytical chemistry and electrochemistry.
Nan Marie Jokerst, a professor in the School of Electrical and Computer Engineering, was named a fellow of the Optical Society of America "for hybrid integration of optoelectronics onto hosts such as silicon CMOS circuits and polymers, with application to interconnections and computation."
Robert Loewy, chair of the School of Aerospace Engineering, was elected to the executive committee of AHS International, a technical professional society for the advancement of vertical flight technology and its applications.
Suresh Sitaraman, an associate professor in the School of Mechanical Engineering, received the Best Paper of 2000 Award from the journal IEEE Transactions on Components and Packaging Technologies. He co-authored the paper with graduate students Rajiv Raghunathan and Carlton Hanna.
C.P. Wong, Regents' Professor in the School of Materials Science and Engineering, received the IEEE Educational Activities Board Meritorious Achievement Award in Continuing Education "for exemplary and sustained contributions to continuing education in polymer materials for electronics packaging and interconnection worldwide."
John Zhang, an associate professor in the School of Chemistry and Biochemistry, received the U.S. Department of Energy's Defense Programs Early Career Scientist and Engineer Award. The award was recognizes the contributions of outstanding scientists and engineers in the nation's research universities to the department's national security mission.
photo by Gary Meek
For the complete news release,
see
http://gtresearchnews.gatech.edu/newsrelease/BOSE.html.
For additional information, contact Michael Chapman,
School of Physics, Georgia Tech, Atlanta, GA 30332-0430. (Telephone: 404-894-5223)
(E-mail: michael.chapman@physics.gatech.edu)
Like a Balloon
Study supports buoyancy explanation for how volcanic rock rises through the Earth's mantle.
reprinted with permission from Science
For the complete news release, see
http://gtresearchnews.gatech.edu/newsrelease/BUOYANT.html. For additional information, contact James Gaherty, School of Earth and Atmospheric Sciences, Georgia Tech, Atlanta, GA 30332-0340. (Telephone: 404-894-1992)
(E-mail: gaherty@eas.gatech.edu).
From Scientists to Senators
Unique course teaches engineers to communicate with diverse audiences.
photo by Gary Meek
For the complete news release, see
http://gtresearchnews.gatech.edu/newsrelease/ENGCOM.html.
For additional information, contact Mark Prausnitz, School of Chemical
Engineering, Georgia Tech, Atlanta, GA 30332-0100. (Telephone: 404-894-5135)
(E-mail: mark.prausnitz@che.gatech.edu).
Putting Randomness to Work
Unique form of nanoscale random motion may perform key cellular functions.
photo by Gary Meek
For the complete news release,
see
http://gtresearchnews.gatech.edu/newsrelease/KINESIN.html.
For additional information, contact Ronald Fox, School of Physics,
Georgia Tech, Atlanta, GA 30332-0430. (Telephone: 404-894-5260)
(E-mail: ron.fox@physics.gatech.edu).
Faculty Awards and Honors
Georgia Tech faculty and staff receive recognition.
Also see Research Notes news stories.
Contents
Research Horizons
GT Research News
GTRI
Georgia Tech
Send questions and comments regarding these pages to
Webmaster@gtri.gatech.edu
Last updated: Nov. 12, 2001