Thursday, Jan. 28, 1999
Decoherence is our ticket out of the quantum world
The
world of quantum mechanics is exceedingly weird, one in which waves can
act as if they were particles, particles can spontaneously pass from one
side of a barrier to the other and gedanken cats can be simultaneously dead
and alive.
Our everyday experiences, the so-called "classical" world, seem immune from the paradoxes that abound in quantum mechanics, and it's comforting to know that our bedroom furniture won't spontaneously reappear in the kitchen and planets will continue to curl smoothly along their orbital paths. We can rest easy knowing that we reside in a classical world.
But we don't.
Truth is, we live in a quantum mechanical world, as Wojciech Zurek stressed to an audience last Sunday at the American Association for the Advancement of Science annual meeting. Zurek, a physicist in Theoretical Astrophysics (T-6) Laboratory, said, "We don't know any place where quantum theory does not apply. Quantum mechanics works extremely well and we do not know of any conflict between its predictions and experiments.
"We need to study this quantum mechanical world in which we live and understand when and why it appears classical if we want to make good use of the opportunities offered by quantum information," Zurek said.
Zurek explained that what allows the set of experiences we have come to regard as normal to emerge from the collection of microscopic, quantum mechanical interactions that underpin the universe is a process he calls "decoherence."
Decoherence, in brief, describes the constant, tenuous interactions between a system or object and its environment, a set of interactions that allows concrete behaviors to emerge from the multitude of simultaneous possibilities that quantum theory allows.
Quantum theory describes a range of possible, superposed states in which objects exist. In the traditional view, it awaits a measurement by some outside observer to force an object to declare itself as being in one definite state: an electron's spin vector pointing up rather than down, a photon acting like a particle rather than a wave.
Since there is no overworked, microscopic measurer constantly pinning down each quantum mechanical system to choose a final state, how do we get from the quantum world of multitude possibilities to the definite events we experience?
Physicists have pondered this conundrum for most of the century, and this decade decoherence has emerged as the answer, or at least a major part of it, Zurek said. "The quantum view as originally formulated was applied to isolated systems. But in fact, all objects have interactions, no matter how tenuous, with their environment. These interactions are so slight that they don't affect the object; rather, the object leaves an imprint on the environment.
"We live in a sea of photons, for example, and interact with some small fraction of them. So the environment is in some sense in a constant process of monitoring objects," Zurek said.
"Decoherence does not require an apparatus or a direct measurement to make a system declare its state. But neither does it give you an exact answer: it only takes us halfway there. Decoherence provides a menu of allowed states; it's a selection process that disallows flagrantly quantum states of macroscopic objects," Zurek said.
There are macroscopic systems that should exist, save for decoherence, in quantum states of possibilities.
Macrosystems defined as "chaotic" can be analyzed from a quantum mechanical view, and quantum mechanics always works, Zurek emphasized.
"Chaotic systems produce weird superpositions of many possible states, and this condition evolves in a reasonably short time scale," Zurek said. "There are macroscopic, chaotic systems that can get into all sorts of bizarre trouble from a quantum-mechanical perspective."
Hyperion, an odd-shaped moon of Saturn, is known to be a chaotic system as it tumbles along its orbital path, its orientation continually redirected by Saturn's gravitational field. According to quantum theory, it should take less than 20 years for Hyperion to get into a quantum state, in which it would be simultaneously in a non-classical superposition of many orientations.
But, thanks to decoherence, Hyperion's major axis is not simultaneously pointed toward and away from Saturn, awaiting a measurement to define its orientation.
"Hyperion is not isolated," Zurek pointed out, "it is making an imprint on the environment all the time. So decoherence applies and keeps the moon out of quantum trouble.
"Decoherence is exceedingly effective. On the macroscopic level of our everyday experience it works many times faster than anything we can measure," Zurek said. "Quantum mechanics without decoherence leads to a universe of paradoxes -- there is a real conflict.
"Experimental investigation of the middle ground between these two realms is just beginning, driven by both our scientific curiosity about the origins of the classical and by the inevitable encounter with decoherence, which is recognized as the biggest obstacle to an experimental implementation of a quantum computer," Zurek said.
--John R. Gustafson
Lab to provide electrical characterization for novel energy project
As partners in a project that could improve the way electrical energy is delivered in America, scientists at the Lab will be providing special electrical characterization of components used in the first high temperature superconducting transformer installed in a U.S. electric utility network.
Los Alamos is teaming up with ABB, American Superconductor Corporation and Air Products and Chemicals, Inc. to support the development, manufacture, installation and field testing of the HTS transformers.
According to Dean Peterson, Leader for the Superconductivity Technology Center (MST-STC), the Lab will characterize certain wires and coils of various sizes used in the transformers in order to measure their superconducting properties as they relate to fluctuations of temperature and magnetic fields. The Lab will also provide cryogenic engineering support for the project.
"Los Alamos was designated ten years ago as one of three DOE national technology centers for the development and application of high temperature superconductors," said Peterson, "The expertise and facilities we have to offer to development of a HTS electrical transformer was recognized by ABB to be unique."
The bulk of the research work will take place at the Materials Science Laboratory and National High Magnetic Field Laboratory under the direction of Martin Maley from the Superconductivity Technology Center (MST-STC).
Other principal researchers involved in the characterization project include: Heinrich Boenig (MST-NHMFL), James Smith and Jeff Willis of the Superconductivity Technology Center (MST-STC), and Phil Blumenfeld and Dave Daney of Los Alamos's Energy and Process Engineering Gropu (ESA-EPE).
The HTS transformers being tested will offer a number of improvements over conventional power transformers including higher electrical efficiency, smaller size and weight, which increases existing substation capacity and reduces the size of future substations, and a novel liquid nitrogen design that will greatly reduce the potential for transformer fires.
The development and manufacture of the HTS transformer by ABB and its partners is under the auspices of the DOE's Superconductivity Partnership Initiative. American Superconductor and ABB previously worked together to develop the world's first HTS transformer installed in Switzerland in 1997.
--Todd A. Hanson
Traveling exhibit on blacks in the Southwest at Mesa Public Library ends Sunday
Tonya Huntley of Materials Science and Processing (NMT-11) and a member of the Laboratory's African American Diversity Working Group admires two paintings that are part of a traveling exhibit on blacks in the Southwest. The exhibit, sponsored by the African American Diversity Working Group and Mesa Public Library, will be on display through Sunday at the downtown library. "Blacks in the Southwest: 1500-1899" was developed and curated by Cortez Williams of the New Mexico African American Research Group. The exhibit attempts to raise the consciousness of people to include the rich history and many contributions of blacks in the historic Southwest, providing contemporary viewers with a rich and expressive interpretation of the past. The exhibit also provides stories about blacks who played instrumental roles in the historical unfolding of the Southwest. Photo by LeRoy N. Sanchez
Open Network Server request forms due Friday
On Oct. 28, 1998, Director John Browne sent a master management memo calling for an "aggressive effort to increase Laboratory unclassified computer and network security." One of the expected outcomes from this effort is the placement of a restrictive firewall between the Internet and the Laboratory network.
The target date for having all 128.165 machines in the Protected (blue) Network, and behind the firewall is March 15. These networks will be protected from the Internet and Open Network, but will not be firewalled from other 128.165 networks.
If you want any of your machines to remain unprotected, you will need to submit an Open Network Server request form to the Security and Safeguards (S) Division office no later than Friday. This form is available online at http://www.nic.lanl.gov/security/firewall/GreenForm.html.
For more information, see the Jan. 25 Daily Newsbulletin.
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