A rchive Date
[ 11-01-2005 ]
Category
[ Science ]
sub-Categoy
[ Physics ]
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Scientists tackle 'Schroedinger's cat' paradox
By ALEX DOMINGUEZ-- Associated Press
Thursday, January 20, 2000
Physicists say they have managed to nudge atoms back and forth between our everyday world and the strange quantum realm where objects can paradoxically be in two places at the same time.
If physicists can further refine their control over this realm, it could result in incredibly fast quantum computers able to crack even the toughest encryption codes used by conventional computers today.
A cat is placed in a box, together with a radioactive atom. If the atom decays, and the geiger-counter detects an alpha particle, the hammer hits a flask of prussic acid (HCN), killing the cat. The paradox lies in the clever coupling of quantum and classical domains.
Quantum theory was developed and elaborated on in the first third of the 20th century by such figures as Max Planck, Albert Einstein, Niels Bohr and Werner Heisenberg. It radically changed how scientists considered the behavior of matter and energy.
Quantum theory holds that energy, light and matter sometimes behave more like particles than waves. According to quantum theory, objects on the subatomic level can simultaneously be in two places or travel in two directions, or have other properties that seem contradictory in the everyday world around us.
Scientists have achieved quantum states. But in an experiment reported in Thursday's issue of the journal Nature, they were able to move atoms into and out of quantum states with more precision than before.
That kind of control is necessary if scientists are to come up with practical devices that employ quantum principles.
For example, a quantum computer could store information in the quantum states of atoms or molecules instead of in silicon chips. But for such a computer to work, scientists would have to be able to block the outside forces that can cause a quantum state to collapse.
Before the observer opens the box, the cat's fate is tied to the wave function of the atom, which is itself in a superposition of decayed and undecayed states. Thus, said Schroedinger, the cat must itself be in a superposition of dead and alive states before the observer opens the box, ``observes'' the cat, and ``collapses'' it's wave function.
David Wineland and fellow researchers at the National Institute of Standards and Technology in Boulder, Colo., coaxed a beryllium atom in a vacuum to be in two places at the same time -- the paradoxical "Schroedinger's cat" state. The researchers then caused the system to collapse by introducing contact to the outside world.
Austrian physicist Erwin Schroedinger proposed the cat paradox in the early 20th century. He described the hypothetical situation of a cat in a box with vial of cyanide gas capped by a decaying radioactive atom, which would release the poison once it decayed. Under quantum theory, the atom could be in both states, meaning the cat could be both dead and alive.
Cats, however, are too big for the quantum effect to remain in place for very long.
The NIST researchers said they were able to keep a beryllium ion in a Schroedinger's cat-like state for as long as 100 millionths of a second.
To do that, the beryllium atom was cooled to close to absolute zero -- minus 459 degrees -- and isolated from all types of radiation, radio waves and other energy sources.
The researchers then used lasers to force the atom's single electron into two states of spin, which also forced the atom to be in two places at the same time.
The researchers then caused the situation to break down by deliberately introducing contact to the outside world via an electrical field. Then, in some cases, they reversed the process.
The experiments helped the scientists determine what causes a quantum state to collapse.
Simply observing a quantum system can also cause it to revert to a classical, or everyday state. The answer to how to get around that problem still evades Wineland and others. |
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