NIST Physicists Coax Six Atoms Into Quantum 'Cat' State

Science Daily | National Institute of Standards and Technology ^ | 2005-12-03

[sourcery]

Scientists at the Commerce Department’s National Institute of Standards and Technology (NIST) have coaxed six atoms into spinning together in two opposite directions at the same time, a so-called Schrödinger “cat” state that obeys the unusual laws of quantum physics. The ambitious choreography could be useful in applications such as quantum computing and cryptography, as well as ultra-sensitive measurement techniques, all of which rely on exquisite control of nature’s smallest particles.

The experiment, which was unusually challenging even for scientists accustomed to crossing the boundary between the macroscopic and quantum worlds, is described in the Dec. 1 issue of Nature.* NIST scientists entangled six beryllium ions (charged atoms) so that their nuclei were collectively spinning clockwise and counterclockwise at the same time. Entanglement, which Albert Einstein called “spooky action at a distance,” occurs when the quantum properties of two or more particles are correlated. The NIST work, along with a paper by Austrian scientists published in the same issue of Nature, breaks new ground for entanglement of multiple particles in the laboratory. The previous record was five entangled photons, the smallest particles of light.

“It is very difficult to control six ions precisely for a long enough time to do an experiment like this,” says physicist Dietrich Leibfried, lead author of the NIST paper.

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.

Schrödinger’s point was that cats are never observed in such states in the macroscopic “real world,” so there seems to be a boundary where the strange properties of quantum mechanics—the rule book for Nature’s smallest particles—give way to everyday experience. The NIST work, while a long way from full entanglement of a real cat’s roughly 1026 atoms, extends the domain where Schrödinger cat states can exist to at least six atoms. The Austrian team used a different approach to entangle more ions (eight) but in a less sensitive state.

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.

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. For example, current supercomputers would require years to break today’s best encryption codes, (which are used to keep bank transactions and other important information secret) while quantum computers could quickly decipher the codes. Quantum computers also may be useful for optimizing complex systems such as airline schedules and database searching, developing "fraud-proof" digital signatures, or simulating complex biological systems for use in drug design.

Cat states, because they are superpositions of opposite overall properties that are relatively easy to verify, could be useful in a NIST-proposed design for fault-tolerant quantum computers. In addition, cat states are more sensitive to disturbance than other types of superpositions, a potentially useful feature in certain forms of quantum encryption, a new method for protecting information by making virtually all eavesdropping detectable.

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. Six ions entangled in a cat state are about 2½ times more sensitive to external magnetic fields than six unentangled ions, offering the possibility of better magnetic field sensors, or (for fixed external magnetic fields) better frequency sensors, which are components of atomic clocks. In addition, correlations between entangled ions could improve measurement precision, because a measurement of the spin of one of the entangled ions makes it possible to predict the spin of all remaining ions with certainty.

The research was funded by the Advanced Research and Development Activity/ National Security Agency, the Department of Defense Multidisciplinary University Research Initiative Program administered by the Office of Naval Research, and NIST.

More information about NIST research on quantum computing and cryptography, and spin-off applications in measurement science, is available at http://qubit.nist.gov.

As a non-regulatory agency of the Commerce Department’s Technology Administration, NIST promotes U.S. innovation and industrial competitiveness by advancing measurement science, standards and technology in ways that enhance economic security and improve our quality of life.

[sourcery]

Ping

[Fiddlstix]

BTTT

[orionblamblam]

[martin_fierro]

NIST Physicists Coax Six Atoms Into Quantum 'Cat' State

Really, really small kitty ping.

[wotan]

This article is full of mistakes.

[GodBlessRonaldReagan]

a real cat’s roughly 1026 atoms

That's either a really small cat or some mighty big atoms.

[Monitor]

This article is full of mistakes.

They completely misrepresent Schrödinger. Having two atoms spinning in opposite directions is not the same as a single cat being both dead and alive.

[Dr.Zoidberg]

He may have meant 10 to the 26th atoms or 10^26. Which is a wee bit larger than 1026 atoms.

Then again, after a second reading of the article he may have meant exactly what was written.

Public education at it's finest.

[snarks_when_bored]

This article is full of mistakes.

They completely misrepresent Schrödinger. Having two atoms spinning in opposite directions is not the same as a single cat being both dead and alive.

You've not grasped the paradoxicality of the situation being described: each of the six ions is spinning both clockwise and counterclockwise simultaneously. So each ion is manifesting a superposition of classically incompatible states, which justifies the analogy to a cat being both alive and dead simultaneously.

[cgbg]

each of the six ions is spinning both clockwise and counterclockwise simultaneously

I wouldn't believe that even if I saw it--but if I saw it it couldn't be happening anyway. :-)

This stuff reminds me of the square root of -1--it shouldn't exist but it is a useful tool in the real world.

[RobFromGa]

It's not that the cat IS both alive and dead, it's that we can't know which is true. We can only know the probability of the event being true. Only by actual observtaion is the actual state know and then it becomes one or the other.

from whatis.com:

Here's Schrödinger's (theoretical) experiment: We place a living cat into a steel chamber, along with a device containing a vial of hydrocyanic acid. There is, in the chamber, a very small amount of a radioactive substance. If even a single atom of the substance decays during the test period, a relay mechanism will trip a hammer, which will, in turn, break the vial and kill the cat. The observer cannot know whether or not an atom of the substance has decayed, and consequently, cannot know whether the vial has been broken, the hydrocyanic acid released, and the cat killed. Since we cannot know, the cat is both dead and alive according to quantum law, in a superposition of states. It is only when we break open the box and learn the condition of the cat that the superposition is lost, and the cat becomes one or the other (dead or alive). This situation is sometimes called quantum indeterminacy or the observer's paradox: the observation or measurement itself affects an outcome, so that it can never be known what the outcome would have been if it were not observed.

[snarks_when_bored]

each of the six ions is spinning both clockwise and counterclockwise simultaneously

I wouldn't believe that even if I saw it--but if I saw it it couldn't be happening anyway. :-)

You're in good company: as (I think) Feynman said, nobody understands quantum mechanics...you just get used to it.

This stuff reminds me of the square root of -1--it shouldn't exist but it is a useful tool in the real world.

Imaginary numbers—which aren't imaginary at all, of course—play a crucial role in quantum mechanics. Here's a GIF image of the time-dependent one-dimensional Schrödinger equation, which describes how the wave function of a non-relativistic (i.e., slow-moving), undisturbed elementary particle such as an electron evolves over time:

Note the multiplication by i, the square root of -1.

[GodBlessRonaldReagan]

I know - did the author leave off the exponent or is he totally clueless?

[SunkenCiv]

The fog comes
on little cat feet.

It sits looking
over harbor and city
on silent haunches
and then moves on.

- Carl Sandburg

[Mind-numbed Robot]

...it can never be known what the outcome would have been if it were not observed.

The old tree in the forest thingy. Science ain't so hard. :-)

[Paul C. Jesup]

'Clockwise' and 'counterclockwise' is all dependent on point of view in that it depends on whether you are viewing the spinning ball from the top or the bottom of it's spinning axis.

[VadeRetro]

Quantum cat-states ping.

[DoctorMichael]

"..........The ability to exist in two states at once is another peculiar property of quantum physics known as “superposition.”..........."

It always amazes me how beautiful and predictive the fruits of Western 'Scientific' inquiry are and in addition, how it all weaves together into a single unbroken tapestry as part of our civilization.

However, there are those that believe.............

1) There is no such thing as an atom.
2) The Earth is flat.
3) Evolution is false.

[PatrickHenry]

SciencePing

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