QUANTUM WEIRDNESS: A scanning electron microscope image of the resonator
Image: O'Connell et al./Nature
PORTLAND, Ore.—What's the sound of one molecule clapping? Researchers have demonstrated a device that can pick up single quanta of mechanical vibration similar to those that shake molecules during chemical reactions, and have shown that the device itself, which is the width of a hair, acts as if it exists in two places at once—a "quantum weirdness" feat that so far had only been observed at the scale of molecules.
"This is a milestone," says Wojciech Zurek, a theorist at the Los Alamos National Laboratory in New Mexico. "It confirms what many of us believe, but some continue to resist—that our universe is 'quantum to the core'."
Physicists have long known that, following the laws of quantum mechanics, objects at the scale of atoms or smaller can exist in multiple simultaneous states. For example, a single electron can move along multiple different paths or an atom can be placed in two different places, simultaneously. This so-called superposition of states should in principle apply to larger objects, as well, as in the proverbial thought experiment in which a cat is simultaneously dead and alive. And in recent years various teams have shown that the weird phenomenon does occur among objects as big as molecules, and also in truly macroscopic systems such as electrical currents in superconductors.
In the new experiment Aaron O'Connell, a graduate student at the University of California, Santa Barbara, and his co-workers have shown for the first time that larger objects can also be in two places at once. "It tells us that quantum mechanics works for macroscopic objects in space," says O'Connell, who presented the results here at a meeting of the American Physical Society. The results were also published online Wednesday in Nature. (Scientific American is part of Nature Publishing Group.)
The team used computer-chip manufacturing techniques to create a mechanical resonator—akin to a small tuning fork. The device is a piece of piezoelectric material (a material that expands or contracts in the presence of an electric field as well as generates an electrical field when put under stress) sandwiched between two layers of aluminum, which act as electrodes. It is one micron thick and 40 microns long, just enough to be visible "with your naked eye," O'Connell says.
The resonator's electrodes are attached to an electronic readout based on superconducting circuits, and the whole contraption is kept in a vacuum and cooled to within 20 thousandths of a degree above absolute zero. But the electronic circuitry can also be used to apply a voltage to the electrodes, so that the team can get the resonator to expand and contract at will. This motion takes place at a characteristic, or resonant, frequency of six gigahertz, or six billion cycles per second. (Tuning forks also have a resonant frequency—in the order of kilohertz—but the mode of resonant vibration in that case is to oscillate sideways rather than to expand and contract.)
The team's first result was to show that at such chilly temperatures the width, or amplitude, of the resonator's vibration becomes quantized—in other words, there is a small amount of vibrational energy, called a phonon, below which the resonator is essentially still. The existence of discrete packets of energy is a hallmark of quantum behavior, and phonons are the mechanical equivalent of light's photons—they are the ultimate, indivisible quanta of vibration, whether thermal or acoustic.
Next, the team put the superconducting circuit into a superposition of two states, one with a current and the other one without. Correspondingly, the resonator was in a superposition of vibrating and not vibrating. These quantum states continued for about six nanoseconds—about as long as the team expected—before fading away.
In a vibrating state each atom in the resonator only moves by an extremely small distance—less than the size of the atom itself. Thus, in the superposition of states the resonator is never really in two totally distinct places. But still, the experiment showed that a large object (the resonator is made of about 10 trillion atoms) can display just as much quantum weirdness as single atoms do. "Yup, quantum mechanics still works," says U.C.S.B.'s Andrew Cleland, O'Connell's co-author and adviser. As to how the day-to-day reality of objects that we observe, such as furniture and fruit, emerges from such a different and exotic quantum world, that remains a mystery.
In addition to its theoretical implications, the device could also find applications in the study of phonons that occur in nature, because a phonon that perturbs the resonator can be detected through the electronic circuit—it is essentially a quantum microphone. "This is a fantastically sensitive detector of acoustic vibration," Cleland says. In principle, one could even place molecules on the resonator and "hear them" interact, chemically or otherwise.
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28 Comments
Add CommentThis is a great step forward in our understanding. Think about the possible future implications of mastering this: faster than light communication by altering the state of an object that exists simultaneously both at the transmitting end and the receiving end of the transmission. Possibly one day even FTL/non-linear space travel. The potential truly is quite spectacular.
Reply | Report Abuse | Link to thisMichael F - I think your imagination just made a quantum leap or two, anyway. This may have more to do with synchronizing the quantum states of molecules than zipping across the universe.
Reply | Report Abuse | Link to thisThis is extremely interesting. I expect these results will require extensive interpretation by quantum physicists.
So let me get this straight. A highly detailed - yet easily understandable article - on quantum mechanics is able to be written by a journalistic.
Reply | Report Abuse | Link to thisWhy doesn't this author detail the effects of health care bill? He would be the first to do so.
The article states that the resonating device is one micron thick, consisting of piezoelectric material sandwiched between two layers of aluminum. It is just 40 microns long, making it just visible to the naked eye. The article does not state how thick the piezoelectric material is: it is this material that is resonating in response to the electric current.
Reply | Report Abuse | Link to thisIf the piezoelectric material is not much more than one molecule thick, it would seem that its quantum scale resonance is not a macroscopic manifestation of quantum effects. The molecules would all be synchronously responding, at quantum scales, to the electric current. The fact that the piezoelectric material is a component in an aluminum macroscopic structure would be coincidental to the quantum piezoelectric effect.
I must say I don't understand what the following really means: "in the superposition of states the resonator is never really in two totally distinct places. But still, the experiment showed that a large object (the resonator is made of about 10 trillion atoms) can display just as much quantum weirdness as single atoms do."
Reply | Report Abuse | Link to thisWas the resonator in two distinct places or not? What is the proof exactly that the resonator was in a superposition of vibrating and not vibrating?
bertrand_ducharme - My guess is that the author should have stated: "in the superposition of states the resonator is never really in two totally distinct places at once."
Reply | Report Abuse | Link to thisThe author's statement: "But still, the experiment showed that a large object (the resonator is made of about 10 trillion atoms) can display just as much quantum weirdness as single atoms do." is likely false, since piezoelectric atoms were likely responding individually, each producing the quantum effect.
I think it's necessary that the author respond to clarify these issues.
Correct me if I'm wrong, but the vibrations were on the atomic level, not the macro level, so there was no macro manifestation of vibration. The macro element was the resonator, but the quantum effect was the vibration, which was at the subatomic level. In other words, this is NOT an example of macro quantum effects, but rather subatomic quantum effects produced on a macro substrate.
Reply | Report Abuse | Link to thisThe author clearly states "[C]orrespondingly, the resonator was in a superposition of vibrating and not vibrating" and later "[T]hus, in the superposition of states the resonator is never really in two totally distinct places." All that shenanigan about a thing being in two places at once is mentioned only to show this experiment is comparable in "weirdness." However, technically it may be interpreted correctly that it's in two places at once, depending on the means and widths of the wavefunctions.
Reply | Report Abuse | Link to thisAgain, the author should clarify the confusion resulting from this article and defend the assertion that quantum effects have been produced at macroscopic scales, lest the more imaginative and enthusiastic readers be led to believe that universal quantum leaps by Schrödinger's cat are just around the corner.
Reply | Report Abuse | Link to thisPlease, SciAm, clarify these issues.
They need a better explanation of what was actually being measured during the "superposition" states. As far as I understand, the resonator is driven by a superconducting circuit that also measures whether the resonator is vibrating. So they put the circuit in a superposition state, and then claim that the resonator is in a superposition because the circuit is in one? There seems to be a measurement problem here. All the same, the ability to detect single phonons with this resonator is amazing on its own.
Reply | Report Abuse | Link to thisTo those seeking clarification, why not go straight to the source? The original article was published in Nature. From the abstract:
Reply | Report Abuse | Link to this"Here, using conventional cryogenic refrigeration, we show that we can cool a mechanical mode to its quantum ground state by using a microwave-frequency mechanical oscillatora quantum drumcoupled to a quantum bit, which is used to measure the quantum state of the resonator. We further show that we can controllably create single quantum excitations (phonons) in the resonator, thus taking the first steps to complete quantum control of a mechanical system."
alexoneal - I and apparently you do not have access to the complete article in "Nature". I refer only to the SciAm article.
Reply | Report Abuse | Link to thisThe author seems to imply that the device demonstrates the uncertainty principal, referring to Schrödinger's cat in the subtitle and stating in the opening paragraph:
"...and have shown that the device itself, which is the width of a hair, acts as if it exists in two places at once—a "quantum weirdness" feat that so far had only been observed at the scale of molecules."
In the next to last paragraph, the author states:
"In a vibrating state each atom in the resonator only moves by an extremely small distance—less than the size of the atom itself. Thus, in the superposition of states the resonator is never really in two totally distinct places."
This deceptive reporting confuses a difficult subject in the interest of making the article more appealing to a naive audience. Opening an article with exciting but misleading remarks leads a casual reader to jump to incorrect conclusions as evidenced by the first commentator. That the earlier ambiguities are later moderated does not excuse the initial misrepresentation of the facts.
How do we belive only our common sense (eye ear tounge nose skin awareness).THE THINGS that you can not sense have no state right.NIRVANA.....
Reply | Report Abuse | Link to thisAs a "naive" reader it seems to me to be an experiment requiring a vast support in the form of equipment.
Reply | Report Abuse | Link to thisI wonder where is the state of consciousness in this?
Can my consciousness effect things at this level?
I think this is the old 'rub two quarters together trick.'
Reply | Report Abuse | Link to thisIt would be valuable to see the results from different size resonators, especially much smaller ones.
Reply | Report Abuse | Link to this"Macro-Weirdness: "Quantum Microphone" Puts Naked-Eye Object in 2 Places at Once"
Reply | Report Abuse | Link to this"Thus, in the superposition of states the resonator is never really in two totally distinct places."
What the hell, people?
Isn't that similar to playing any instrument in the same room as a piano. The piano string of the note you are playing starts to resonate without touching the piano.
Reply | Report Abuse | Link to thisThis seems to confirm the idea that parts of the human brain may be quantum in nature. And, may exist in in multiple dimensions at the same time???
Reply | Report Abuse | Link to thisHowever this experiment is interpreted it is still an amazing result. Could there be quantum resonators in our brain cells??
Reply | Report Abuse | Link to this@oldshelly, where do you get that?! You have a strange definition of the word confirm. It seems to mean, something that can be twisted by an over active imagination to imply anything. You need to get back on your meds.
Reply | Report Abuse | Link to thisAfter reading this article, I was just beside myself.
Reply | Report Abuse | Link to thisThe superposition, even at microKelvin, only lasted nanoseconds. Our brains aren't at microKelvin.
Reply | Report Abuse | Link to thisQuantum physics determines almost every property of matter. So, it is extremely important to how our brains, or anything else works. But, if you are looking for new "metaphysics" to come from an experiment like this, you will be disappointed.
This experiment isn't really that surprising, but it is the first example of something so large being put into a superposition of states (and actually proven to be such).
I simply don't understand how the superconducting circuit can both carry a current, and not carry a current, i.e. electrons must be both moving and not moving at the same time!!!
Reply | Report Abuse | Link to thislarge objects give an average effect, dead and alive makes the cat half dead..
Reply | Report Abuse | Link to thisThis article itself is an exercise in understanding quantum effects: it's in the paradoxical "superposition" of stating that this little resonator is in multiple locations and isn't at the same time. Literary irony - or just sub-par journalism?
Reply | Report Abuse | Link to thisThe "quantum microphone" is based on a single electron transistor, that is, a transistor where the current passes one electron at a time. The acoustic waves studied by the research team propagate over the surface of a crystalline microchip, and resemble the ripples formed on a pond when a pebble is thrown into it.
Reply | Report Abuse | Link to this<a href="http://www.blacksmithsurgical.com/surgical-instruments/tuning-forks">Tuning Forks</a>
Chilling a bit of material so close to absolute zero that it makes the responses ridiculously sluggish, then flick the light switch a bunch of times really fast to get it to react multiple ways throughout the object as the motion delay progresses from the point of origin. Woohoo.
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