Posted on 12/03/2005 10:24:55 PM PST by 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.
This works in a cool way. You basically send your message via pulses of cat-state particles of which each is entangled with a particle you are NOT sending. If the cat-state of your stay-at-home particles collapses too soon, some eavesdropper has sensed your message along the way.
Why shouldn't it exist? I would imagine that it's as real as any other number. (Note the complex sentence.)
The real question (IMNSHO) is: "Why does the Sqrt(-1) suffice?" In other words, why do we not need CubeRoot(-1), etc.?
I'm thinking that should be "10^26 atoms"
otherwise, interesting indeed.
I agree with Einstein: entanglement IS spooky.
I cannot help but wonder whether entanglement might lead to instantaneous communication over practically infinite distances.
corollary: if it can, then I cannot help but think that perhaps the SETI folks have been barking up a very wrong tree in listening for alien radio comsig.
That's not correct. The two states are simultaneously "real" at the 50% level. Quantum superposition is a statement about reality, and not only about our knowledge of reality.
Einstein shared your misconception, and insisted that the two would be experimentally indistinguishable in any case. After his death, however, it was discovered that he was wrong: indeterminate states behave differently from merely undetermined states. The latter will obey Bell's Inequality when you compare correlated measurements; the former will violate it.
The experimental fact is that entangled states yield measurements that violate Bell's Inequality.
Doesn't work that way. You can't send information faster than light.
Here is the original press release. You can see that the "26" is superscripted. The "1026" was a copy-and-paste job from the original, nothing more.
are you sure?
last I checked - the US/German experiment - the implication was instantaneous mirroring of changes irrespective of distance.
I'm just mirroring what I've read. The technique sounds impressive when written about, but I'm pretty sure it doesn't allow communication faster than light.
I'll be the first to admit I'm not even at piker-comprehension concerning QM, so all of this is like nifty sorcerous lunacy to me.
Schrödinger obviously never drank tequila or he would know an entire human body can enter a cat state on any given morning.
So9
Not in classical or relativistic physics you can't, but there are some questions in quantum physics.
Electrons do not move from one orbit to another of an atom, but disapear one place and appear instantaneously in another orbit. There are a nuumber of other quantum transitions that take place without passage of time.
Is information moved? That is the difficult quible.
So9
Point of Information: do you mean "why do we NOT need CubeRoot (-1), etc." in order to model QM, or are you asking the question in a more abstract, purely mathematical sense?
Everything I have read about quantum entanglement suggests it cannot be the basis of faster than light communication.
At the very least it requires you to physically transport the entangled particles to the receiving destination. That pretty much rules out using it to meet alien civilizations.
Time is an illusion. So is space. So is causality. As soon as we perceive the universe correctly, distance will be annihilated, as will past and future.
Perhaps not interstellar communications, but instantaneous communication across the diameter of an atom has profound implications for the ultimate speed of electronics devices of all types.
So9
from what little I have comprehended of what little I have read on the subject, the following is the (quite possibly incorrect impression of) property of entanglement which interests me:
2 entangled particles, separated by significant distance.
perturb one of the particles, and the other particle instantly undergoes the same perturbation.
if this is so, one can consider one state of perturbation a zero, and another state a one, thus creating a binary communicator allowing instantaneous -if absurdly simple- data transfer irrespective of distance.
again assuming all the above, and assuming the number of entangled particles can be jacked up to something more useful, then REAL instant datacomm is possible. the applications would of course include controlling long-range unmanned recon on Earth and (more importantly) in space... no more long waiting periods between command, execution, and reply - it'd become similar to actually being there in real-time, more like controlling an RC car on your lawn.
That'd be damn nifty... if it is indeed possible
well, philosophically I can see how that could be true - only problem: we are PART of the illusion, so to transcend the illusion we would have to completely transcend ourselves.
that can wait till I die, I reckon :)
um, isn't the cube root of "negative one" simply "negative one"?
I mean, -1^3 = -1...
Not at all. We create the illusion. There is nothing in nature that requires the illusion. Just as there are no patterns in nature: we create the patterns. That appears to be our job.
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