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.

[RightWhale]

it all depends on your point of view

That can be altered until facts fit. This was explained to me by Nancy, an elegant and becoming, youngish but mature, lady of exquisite taste and refinement, who, every second Tuesday at ten AM until noon, drops by for a cup of tea.

[King Prout]

thirty days hath Septober, April, June, and no wonder!
All the rest have PEANUT BUTTER,
All, except my dear Grandmother...
She had a little red tricycle...
I stole it.

[RightWingAtheist]

They never talk like this on Kos or DU :-)

[King Prout]

hehhehheh

[bobdsmith]

Sure, i and -i.

cool, thanks for the answer

[snarks_when_bored]

There's a report on this work at the PhysicsWeb site, here:

Entanglement reaches new levels

Here's the photo from that link:

There's also a link to a QuickTime animation of the six entangled ions:

Animation

The caption for the animation reads as follows:

The above animation simulates six ions in "cat" states, spinning in two opposite directions at the same time. Each ion spins both left (clockwise, shown in blue) and right (counter-clockwise, shown in red) simultaneously, a condition called a superposition. The six ions are also entangled with each other, so their properties are correlated. If one ion is measured with a laser (shown as a blue beam), that ion's delicate superposition will "collapse" and it will spin in only one direction (clockwise/blue in the animation). Entanglement causes the other five ions to immediately spin in the same direction (they all turn blue).

It's worth keeping in mind that this entanglement is not (in the general case) dependent on how far apart the entangled particles are when a measurement is made. That is, if particles A and B are spin-entangled and head off in opposite directions from each other, and if the spin state of particle A is finally measured 5 billion light years away from its source, then the spin state of particle B (which is also 5 billion light years away from its source, but 10 billion light years away from particle A) is at the instant of measurement determined (whereas before A's state was measured, B's state was not determined). This is what Einstein called "spooky action at a distance" ("spukhafte Fernwirkungen").

[King Prout]

okay... but... does this mean you MIGHT be able to use entanglement for long-distance data comm?

[snarks_when_bored]

okay... but... does this mean you MIGHT be able to use entanglement for long-distance data comm?

Not according to present understanding...sorry, bud! (laugh) Whatever sort of connection the entangled particles are manifesting, it is not a data channel through which information could flow.

[King Prout]

drat.

[snarks_when_bored]

Yeah, woulda been sweet...

[Oberon]

Doesn't work that way. You can't send information faster than light.

Not according to current theory, at any rate. However, the propagation rate of entaglement...if there is one...is a question ripe for at least one doctoral dissertation and probably several in the not-so-distant future.

[mikegi]

superposition

Superposition is just a mathematical device used to analyze linear problems. It isn't "real". I see this same misconception in signal analysis - a signal isn't the sum of sine waves.

[snarks_when_bored]

Does sqrt(-1) have two roots?

Sure, i and -i.

DS, I'm sure you meant to say that i and -i are the two square roots of -1, not of sqrt(-1)=i ...

[Doctor Stochastic]

Sorry, I misread. (I'll have to get better peer review.)

Sqrt(-1) does have two square roots.

[Theophilus]

...
3) Evolution is false.

And then there are those who believe, given enough time of course and as long as nobody peeks, that Schrodinger's cat will spontaneously regenerate and evolve back into himself from his own carcass. Oh happy delusion!

[r9etb]

Public education at it's finest.

See if you can spot the irony....

[snarks_when_bored]

Sorry, I misread. (I'll have to get better peer review.)

Sqrt(-1) does have two square roots.

Figured as much, and, yep, it does...

[Dr.Zoidberg]

So I had a spare apostrophe. If you don't use them they go stale.

'''''''''

[grey_whiskers]

Quaternions were quite an innovation, but turned out to be not particularly useful and were abandoned--until a few years ago. They are back, especially in graphics.

They are sometimes useful in molecular dynamics when calculating rotational energy, when the sine term in the denominator leads to singularities...

[grey_whiskers]

Hamilton was so impressed with his spatiotemporal Dublin insight that, not having pencil and paper handy, he made his wife wait on their Sunday stroll while he carved the equation--Daniel Boone in the wilderness of Kentucky making note on a tree of a meeting with a bear--into the stone of Broome Bridge on their path.

Did I miss something, as usual?