Six atoms in quantum 'cat' state
In this news release, researchers from the U.S. National Institute of Standards and Technology (NIST) report that they have demonstrated for the first time that six charged atoms of beryllium, or ions, could collectively spin clockwise and counterclockwise at the same time. This so-called Schrödinger 'cat' state could lead to new applications in quantum computing and cryptography, as well as ultra-sensitive measurement techniques.
First, here is some background about what is called the Schrödinger's cat state.
The ability to exist in two states at once is another peculiar property of quantum physics known as "superposition." The NIST ions were placed in the most extreme superposition of spin states possible with six ions. All six nuclei are spinning in one direction and the opposite direction simultaneously or what physicists call Schrödinger cat states. The name was coined in a famous 1935 essay in which German physicist Erwin Schrödinger described an extreme theoretical case of being in two states simultaneously, namely a cat that is both dead and alive at the same time.
Below is an image showing how six charged atoms are at the same time spinning clockwise and counterclockwise (Credit: Bill Pietsch, Astronaut 3 Media Group, Inc., for NIST).
For your viewing pleasure, here are two links to a larger version and to a short animation simulating six entangled ions in simultaneous 'cat' states (QuickTime format).
Here are some details about the experiment.
In the NIST experiment, the ions are held a few micrometers apart in an electromagnetic trap. Ultraviolet lasers are used to cool the ions to near absolute zero and manipulate them in three steps. To create and maintain the cat states, the researchers fine-tuned trap conditions to reduce unwanted heating of the ions, improved cooling methods, and automated some of the calibrations and other formerly manual processes. One run of the experiment takes about 1 millisecond; the cat states last about 50 microseconds (about 1/20 as long). The team ran the experiment successfully tens of thousands of times, including numerous runs that entangled four, five, or six ions.
But what will this be useful for?
Entanglement and superpositions are being exploited in laboratories around the world in the development of new technologies such as quantum computers. If they can be built, quantum computers could solve certain problems in an exponentially shorter time than conventional computers of a similar size.
But this also could be useful for other applications.
The entangled cat states created by the NIST researchers also might be used to improve precision instruments, such as atomic clocks or interferometers that measure microscopic distances, offering the possibility of better magnetic field sensors, or (for fixed external magnetic fields) better frequency sensors, which are components of atomic clocks.
This research work has been published by 'Nature' under the title "Creation of a six-atom 'Schrödinger cat' state" (Volume 438, Number 7068, Pages 639-642, December 1, 2005). Here is a link to the first paragraph of this letter to the editors of the scientific journal.
And if you want to learn more about these experiments, you'll see at the bottom of this page at NIST how the scientists created entangled cat states with six ions.
Sources: NIST news release, via EurekAlert!, November 30, 2005; and various web sites
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