Skip to comments.Physicists Put the Quantum Into Mechanics
Posted on 06/08/2009 7:43:15 PM PDT by neverdem
Spooky connection. Physicists forged a quantum link called entanglement between the mechanical oscillations of one pair of ions and another distant pair.
Credit: John Jost and Jason Amini/NIST
Quantum mechanics and its bizarre rules explain the structure of atoms, the formation of chemical bonds, and the switching of transistors in microchips. Oddly, though, in spite of the theory's name, physicists have never made an actual machine whose motion captures the quirkiness of quantum mechanics. Now a group from the National Institute of Standards and Technology (NIST) in Boulder, Colorado, has taken a step in that direction by forging a mind-bending quantum connection between two mechanical widgets. Their devices don't look like electric drills or other familiar machines, however: Each is a pair of ions oscillating in an electric field, like two marbles joined by a spring.
The link the researchers created is called entanglement, and it has been made before between certain internal properties of quantum particles, such as the inner gyrations of ions. The new work extends that link to the actual motion of the ions, which is a kind of micro-analog of the swinging of the pendulum of a grandfather clock. "For the first time, the mechanical motion itself has been entangled," says Rainer Blatt, an experimental physicist at the University of Innsbruck in Austria.
To appreciate what the NIST researchers have done, an aficionado has to get his head around two very weird concepts in quantum mechanics. First, quantum theory says that an object can literally be in two contradictory states at the same time. So whereas an office chair can spin either to the right or to the left, a quantum particle like an ion can literally spin in two opposite directions--call them up and down--at once. That mind-creasing "superposition" state lasts until an experimenter measures the ion's spin, at which point the ion instantly "collapses" to one direction or the other. Weirder still, two ions can be put into these uncertain two-ways-at-once states and then linked up so that, even though it's impossible to say which way either is spinning, their directions are completely correlated. For example, if the first one is measured and collapses into the up state, the second one will instantly collapse into the down state, even if it's light-years away. That connection is called entanglement, and anyone who finds it hard to swallow is in good company: Einstein famously called it "spooky action at a distance."
To extend such a connection to mechanical motion, NIST's John Jost, David Wineland, and colleagues used electric fields to trap two beryllium ions and two magnesium ions. They then applied a magnetic field and pulses of laser light to entangle the spins of the beryllium ions. After that, they separated the ions into two beryllium-magnesium pairs, which would be their mechanical widgets.
During this process, the beryllium spins remained entangled, and the researchers next transferred that link to the motion of the pairs. To do that, they zapped each beryllium with a laser again to "rotate" the down-spinning half of its split personality back to up while leaving the up-spinning half untouched. But they tuned the energy of the laser so that as the down-spinning part of the beryllium's state turned, the light would also excite the ions in the pair to oscillate. As a result, each beryllium ion spun only up, but each beryllium-magnesium pair was left in a state in which it was both oscillating and not-oscillating. Moreover, because the two beryllium spins started out entangled, the two oscillatingnot-oscillating pairs ended up entangled, too, the researchers report this week in Nature.
"It's a completely amazing experiment," says Jack Harris of Yale University, one of a number of physicists striving to show quantum effects in vibrating beams and other "macroscopic" mechanical devices. The ion experiment hasn't beaten their efforts to the punch, he says, because although it entangles mechanical motion, the ions themselves are still quantum particles. "It's more the macroscopic than the mechanical that we're after," Harris says. Indeed, he and others hope to test whether some as-yet-undiscovered principle forbids quantum weirdness in objects containing many billion atoms.
For their part, NIST researchers hope to use ions to fashion a quantum computer that, thanks to quantum weirdness, could solve problems that stymie conventional computers. "A lot of the technologies we developed for this experiment are going to be crucial for making a quantum computer with trapped ions," Jost says. However, making a quantum computer will likely be even harder than making a rudimentary quantum machine.
My brother, Yale Math and Physic Ph.D, could get a start on it, but not me. I can follow the arguments conceptually in many cases, however.
Quantum theory does not predict causality violation. The apparent violation of causality is a result of trying to model the quantum events classically, which is a purely rhetorical exercise, and bound to increase confusion.
Is it really 'communication'?
Or is it the result of matched sets which must maintain a balance?
Like a teeter-totter. If one pushes down on the seat, the other seat, around eight feet away, instantaneously goes up.
The mystery, to us, is the pipe in the middle.
But, he had more 'imagination', I would guess. And maybe a greater ability to communicate to others at their own level.
It should be regarded as a quantum-style conservation law, in this case conservation of spin angular momentum. (teeter-totter)
I thought we already had quantum computers that used entanglement. (?)
Kant’s theory was that space and time are just “the forms of understanding”. IOWs these are the way WE understand reality. The real world could very well not abide by “our” rules of space and time. When looked at this way, quantum mechanics don’t appear so mysterious.
Exactly. There is NO indication that this “action” exceeds light speed.
Then there’s the Carlos Castaneda approach to reality.
NYT will report, “Atom collapses. Femtrons and minoritrons hit hardest.”
That mind-creasing "superposition" state lasts until an experimenter measures the ion's spin, at which point the ion instantly "collapses" to one direction or the other.
Or perhaps there is no objective collapse, and the world splits into two worlds, one in which the ion spins up and one in which the ion spins down.
LOL, I sometimes wonder if Carlos hadn’t read Berkley and Kant. Remember the incident he describes in one of his books involving the Mexican Air Force jet that seemed to violate causality?
“LOL, I sometimes wonder if Carlos hadnt read Berkley and Kant. Remember the incident he describes in one of his books involving the Mexican Air Force jet that seemed to violate causality?”
Well, he was known as a voracious reader of books, it being noted that wherever he lived was stacked to the ceiling with them.
However, his emphasis was always perception, not defining what was possible to perceive, it being far too complex to grasp all at once. So what we think is cause and effect may not be. Nor may they be in the right order.
Castaneda puts a great deal of emphasis on the unreliability of ordinary memory, but we are reliant on memory and assumptions to make the cause and effect association.
I remember a friend’s story of his meeting with a rural peasant in the Chiapas area of southern Mexico. The two went to a Pemex station far from the peasant’s home, and went into the restroom. The peasant was amazed and perplexed at water coming out of the sink faucet, but could not associate that with the act of turning the sink knob on and off. He had no grasp of the machinations involved.
From his point of view, turning the knob to produce water was like waving your hands in the air to make a magical gesture. It made no sense. He was shown it several times, but still tried to grab the faucet and shake it to make water come out.
As pitiful as it sounds, the peasant was really stuck in that mindset, and would have needed considerable training to learn even the basics of modern society. It was an alien zeitgeist.
However, we should not be very confident, either, because our mindset is just as contained. To make matters worse, there is an inherent limitation to mechanical complexity, in which fewer and fewer people actually understand what is involved. To the rest of us, it just “works”, but we have little or no idea why. Already our society is experiencing peripheral problems with legacy technologies that no longer have experts familiar with their use.
Ironically, Castaneda pointed to this as one of the reasons that the culture of the old sorcerers collapsed. Knowledge became complex and specialized, which made it brittle. Then people entered the situation with a different zeitgeist, and bonked them on the head.
Clueless layman question: How does one determine that a particle is in superposition since measuring it causes the “collapse” into one state or the other?
Ask me about chemistry or the life sciences. I have just as many questions as anybody else about quantum mechanics.
A particle can be described as also being a wave. When that's done, the particle is represented by a wavefunction. In short, the wavefunction squared gives the probability that the particle will be in some particular state. So, the calculation, which represents the behavior of reality, involves probabilities and not certainties regarding the values particular to the possible state of the particle. That means before each look at a particle, the particle is considered to be in a superposition of all the possible values it can have. That includes when one takes a second look at the same particle.
In cases like the one in the article though, the state is a single many particle state of a system that involves the values of 2 particles and the vaue of the state of the system. That means the values are limited and certainties and distinguishability enter the picture. So if one has information about one, or more of the particles that are linked by being in the same system state, they have information about the value(s) of other particle(s) by virtue of knowing the value(s) for the state of the system.
In the first case, the particles were free and even if they were not and there was a common state, no initial info was known. Since the laws of physics must be consistent, each measurement of a free particle will be consistent with a probability and not certainty. That applies even if it's the same particle and a measurement that indicated it was "up" was obtained. That behavior, or peculiarity of reality makes it appear as if the particle "collapses" back to a state that consists of a superposition of values. ...like an exposed card that's shoved back into the a deck that's subsequently reshuffled.
The details begin to be understood when one considers that "particles" arise out of fields and the particles are described by superimposed, time varying sinusoids. In general, it's the phase of the representative waves that change, that causes the "collapse" type description. Phase velocities can be faster than light, but all that obtains from that is a slower than light speed, wave envelope shape change. The particles represented by the amplitudes of the field(s) never move faster than light, nor do they communicate(exchange energy) faster than light, but the phases of the sinusiods that make up the field(s) envelopes do.
If one has 2 particles in a particular system, the state is known and a relavant pair value for one of the particles is known, the other must be fixed to the opposite, or some other value that maintains the overall fixed the system value(s). In general, that's because the particle's wave components are phased to accomodate their membership in the system with a particular state. System membership in the article is called entanglement. The particles in any such system can not be in a collapsed state, because they're constantly being looked at by the other particles in the system. ie. the phases of the sinusoids that represent the particles are locked so that the system's value(s) remain fixed.
Thanks for the explanation. It actually helped a lot. :-)