Search for the bridge to the quantum world

Jul 02, 2010

Science fiction has nothing over quantum physics when it comes to presenting us with a labyrinthine world that can twist your mind into knots when you try to make sense of it.

A team of Arizona State University researchers, however, believe they've opened a door to a clearer view of how the common, everyday world we experience through our senses emerges from the ethereal quantum world.

Physicists call our familiar everyday environment the classical world. That's the world in which we and the things around us appear to have measurable characteristics such as mass, height, color, weight, texture and shape.

The quantum world is the world of the elemental building block of matter - atoms. Atoms are combinations of neutrons and protons and electrons bound to a nucleus by electrical attraction.

But most of an atom - more than 99 percent of it - is empty space filled with invisible energy.

So from a quantum-world view, we and the things around us are mostly empty space. The way we experience ourselves and other things in the classical world is really just "a figment of our imaginations shaped by our senses," explains ASU Regents' Professor David Ferry.

For more than a century, scientists and engineers have struggled to come to a satisfactory conclusion about the missing link that bridges the classical and quantum worlds and enables a transition from that world of mostly empty space to the familiar environment we experience through our senses.

One proposed scenario based on these questions was investigated in a dissertation written by Adam Burke to earn his doctorate in electrical engineering in 2009 from ASU's Ira A. Fulton Schools of Engineering.

To try working out an answer to some of the questions, Burke teamed with Ferry, a professor in the School of Electrical, Computer and Energy Engineering, Tim Day, who recently earned his doctorate in electrical engineering from the school, physicist Richard Akis, an associate research professor in the school, Gil Speyer, an assistant research scientist for the engineering schools' High Performance Computing Initiative, and Brian Bennett, a materials scientist with the Naval Research Laboratory.

The result is an article published recently in the research journal Physical Review Letters and featured on PhysOrg.com, a science, technology and research news website. It describes the transition from quantum to classical world as a "decoherence" process that involves a kind of evolutionary progression somewhat analogous to Charles Darwin's concept of natural selection.

The authors built on two theories called decoherence and quantum Darwinism, both proposed by Los Alamos National Laboratory researcher Wojciech Zurek.

The decoherence concept holds that many quantum states "collapse" into a "broad diaspora," or dispersion, while interacting with the environment. Through a selection process, other quantum states arrive at a final stable state, called a pointer state, which is "fit enough" (think "survival of the fittest" in Darwinian terms) to be transmitted through the environment without collapsing.

These single states with the lowest energy can then make high-energy copies of themselves that can be described by the Darwinian process and observed on the macroscopic scale in the classical world.

The experiments arose from using advanced scanning gate microscopy to obtain images of what are called quantum dots.

Burke, now doing research in a post-doctoral program at the University of New South Wales in Sydney, Australia, explains it like this:

Imagine the quantum dot as a billiard table in which the quantum point contacts are the two openings through which a ball could enter or leave the dot, and the interior walls of the dot act as bumpers.

If there were no friction on the table, a billiard ball with an initial trajectory would bounce off of these walls until eventually finding an exit and leaving the dot (this is the decoherence part).

Or it might find a trajectory that does not couple to the openings and would therefore be a surviving pointer state, what is called a diamond state.

One difference between the classical physics of billiard balls and the quantum physics of electrons is that an electron can tunnel through "forbidden phase space" to enter this diamond state, whereas a billiard ball entering from outside the dot would not find itself able to reach this diamond trajectory.

It is this isolated classical trajectory, and the buildup of an electron wave functions' amplitude along that trajectory, that is referred to as a scarred wave function.

To experimentally measure these scars, imagine that we can't see inside the walls of our billiard table, but we can count the billiard balls exiting the table. This is what is normally measured with the conductance of the quantum dot and its environment.

"We measure the current through the dot, the numbers of 'billiard balls' passing through it per second, to try to see how this changes when we move our probe around the 'billiard table,' " Ferry says.

Furthermore, there is the probe of the scanning gate microscope, which applies a small electric field. This can be pictured as a small circular bumper on the billiard table that can be moved around within the dot.

This small "bumper" is rastered left to right, top to bottom over the area of interest. If a ball is traveling along this diamond pattern it is perturbed by the bumper when it rasters into the trajectory.

Think of rastering like the way a television image works, with a pattern of scanning lines that cover the area on which the image is projected, or a set or horizontal lines composed of individual pixels that are used to form an image on a computer screen.

When this happens, the ball bounces off the perturbation, and takes a new course within the dot until finally coupling out one of the openings to be measured. The change in the ball's motion appears as a change in the conductance - the number of balls going through the openings in a given time.

Ferry explains: "With scanning gate microscopy, we monitor where these changes occur within the scans, and hopefully this gives us a map of the scarred wave functions corresponding to the pointer states."

Quantum mechanically, he says, a new electron will tunnel right into the diamond state, so the measurement can continue until the whole area is mapped.

The data that came from the team's experiment supports Zurek's theories of decoherence and quantum Darwinism, Burke says.

Ferry says these findings are just one step in a process that is open to conjecture, but they point toward a "smoking gun" for the existence of this quantum Darwinism and a new view in the search for evidence of how the quantum-to-classical world transition actually occurs.

If you can wrap your mind around all this, he says, "You open the door to a deeper understanding of what is really going on" at the core of physical reality.

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GSwift7
1.7 / 5 (3) Jul 02, 2010
Okay, that's creepy stuff to think about. I'm having trouble understanding the analogies here. How does this fit with the idea that entropy must always increase in the universe? Darwinism suggests a tendency of increased organization, which makes sense in biology, but shouldn't there be a tendency for things to lose order over time in physics? This survival of the most organized state doesn't seem to match what we observe on the macro scale. Are they saying that the decoherence is really dominating, but we just happen to observe the part that's left over?

I struggle with this kind of stuff. It makes my brain hurt trying to visualize it.
aintry
Jul 02, 2010
This comment has been removed by a moderator.
Hesperos
1 / 5 (1) Jul 02, 2010
Okay, that's creepy stuff to think about. I'm having trouble understanding the analogies here. How does this fit with the idea that entropy must always increase in the universe? Darwinism suggests a tendency of increased organization, which makes sense in biology, but shouldn't there be a tendency for things to lose order over time in physics? This survival of the most organized state doesn't seem to match what we observe on the macro scale. Are they saying that the decoherence is really dominating, but we just happen to observe the part that's left over?

I struggle with this kind of stuff. It makes my brain hurt trying to visualize it.

The classical world is the average of the quantum world. Thermodynamics remains valid because the quantum probabilities average out that way. However for individual particles, all bets are off which allows the microscopy. (I used to operate a scanning electron microscope for JHU/APL. Not the same, but close enough to grasp the concept.)
Jigga
1 / 5 (1) Jul 02, 2010
Quantum Darwinism is one of many postmodern theories or rather concepts based on correspondence principle ("everything is somehow connected with everything"), which tend more to "explain", then predict.

http://en.wikiped...arwinism

Main problem is, Darwinian theory has very wide parameter space, so that it's virtually impossible to formalize it for obtaining of some testable predictions. And theories are defined only by their postulate sets...

We can see natural evolution in nearly everything, for example in condensation and coalescence of rain droplets during their fall - but frankly, what could we predict/compute from such "model"? Such perspective is good mainly for writers of esoteric books about quantum mechanics, who need to extend their manuscripts by few easy pages, which contradict to anything from the previous content.
Jigga
1 / 5 (2) Jul 02, 2010
How does this fit with the idea that entropy must always increase in the universe?
Actually this is a very good point. From fundamental Schroedinger equation of quantum mechanics follows, the wave packet of every free particle will always expand into infinity in less or more distant perspective.

So if we can observe some emergence of more compact and complex structures from "ethereal quantum world", we can be 100% sure, what we are observing by now is definitely NOT a QUANTUM phenomena. Or we would only confuse well established terms.
Jigga
1 / 5 (2) Jul 02, 2010
..how the common, everyday world we experience through our senses emerges from the ethereal quantum world...
"etheral" means to "behave like Aether", i.e. to behave like hypothetical omnipresent gas. Such gas is forming both more dense fluctuations, both dissolves them.

While the later process could be interpreted as a quantum entropic process, the former process of fluctuations merging is actually a negentropic one - we can see, aether concept is more symmetric in time and general, then the quantum view, because it can describe both repulsive forces (like the pressure of radiation), both attractive ones (like the condensation and gravity).

Whereas quantum mechanics cannot describe gravity at all - the worse, it contradicts it by its very nature. The connection "aetheral quantum world" is actually an oxymoron.
BadMan
not rated yet Jul 02, 2010
I appreciate the attempt by the researchers, but I doubt the validity of the results. Although quantum dots are a good macroscopic equivalent of a quantum particle, it is still a construct therefore may not be a accurate representation of the quantum processes they are refering to due to the fact that it seems to violate entropy. Granted, I am not an expert, but a violation is a violation neverless. The results are fine for observations of the system of this particular quantum dot, but it is not a definitive explanation of any quantum process.
johanfprins
2.7 / 5 (6) Jul 02, 2010
most of an atom - more than 99 percent of it - is empty space filled with invisible energy.

This is of course absolute nonsense. Where is the "empty space". The nucleus is surrounded by electron-waves; each having energy. Thus, their intensities are energy: This is hardly "empty space". Each wave is an entity!

There is NO break between the "quantum world" and the "classical world" when modelling light and matter ONLY in terms of waves. To thus search for a "bridge" when it is NOT needed is a waste of time and energy!
bluehigh
1 / 5 (1) Jul 02, 2010
Chalk your cues folks. Atomic billiards is back in town. This time though, no bits of solid mass smashing about but some mystical waves bouncing around the tables empty spaces.

Same old question for the promoter of waves only models. Waves of WHAT? Invisible energy of course! Suppose we call the wave-entity a particle. Oh I forgot,we are not discussing reality but just some fictional untestable playstation physics model.

Just smile and wave.
Hesperos
1 / 5 (1) Jul 03, 2010
most of an atom - more than 99 percent of it - is empty space filled with invisible energy.

This is of course absolute nonsense. Where is the "empty space". The nucleus is surrounded by electron-waves; each having energy.

Your word "surrounded" is the problem. QM tells us that particles may only exist in distinct domains.
johanfprins
3 / 5 (2) Jul 04, 2010
Chalk your cues folks. Atomic billiards is back in town. This time though, no bits of solid mass smashing about but some mystical waves bouncing around the tables empty spaces.

The only mystical waves I know about are those that supposedly have intensities each equal to a "probability distribution"; which for most of them give the "most probable" position of a "particle" at a position where the "probability distribution" is zero!: What can be more "mystical" than this?

The compelling experimental evidence from electrodynamics gravity is that BOTH light an matter consist of energy-fields NOT mystical particles. So why do we stick to mystical particles? Only because Bohr's wrong model of the atom assumes that a "particle" can circle a nucleus, even when its energy is less than its rest mass energy! Now this is REALLY mystical is it not?

As soon as I observe a particle at a "most probable position" where the probability is zero to find it, I will gleefully "wave at it".
johanfprins
3 / 5 (2) Jul 04, 2010
Your word "surrounded" is the problem. QM tells us that particles may only exist in distinct domains.

Yes the present incorrect Copenhagen-interpretation of QM tells us that "particles" exist without even defining what is meant by the term "particle". When asking for a definition one sees a lot of waving (of the hands): Thus it MUST still be a wave.

Obviously an electron wave surrounds the nucleus of an atom; or else we would not have had the models of chemical-bonding which the Chemists use with great success. "Electron-particles" do not feature in these models: Why not? Most probably because they just do not exist at all.

As I have said over and over, one can model ALL aspects of QM in terms of waves; also photo-electric ejection of electrons. So why invoke "mystical particles" and "mystical probability waves". Obviously the latter are just pure voodoo.
Jigga
1 / 5 (1) Jul 04, 2010
particle = wave with boundary (condition)

Do you agree with such definition?
Hesperos
1 / 5 (1) Jul 05, 2010
particle = wave with boundary (condition)
Do you agree with such definition?

Concerning the the electron for example, we might wonder: is it a particle which acts like a wave, or a wave which acts like a particle? Fortunately, QM provides the answer. Both! Even Einstein was forced to agree, since E=MC^2.

I worked for JHU/APL for 12 1/2 years performing many analytical tasks including chemistry. Spectroscopy is an excellent tool for that discipline and I became expert at FTIR, AAS and EDS. AAS stands for Atomic Absorption Spectroscopy (look the other 2 up :-) and after spending a few hours slaving over the ground state flame I guarantee that even the most die-hard QM sceptic would become convinced.
johanfprins
3 / 5 (2) Jul 05, 2010
particle = wave with boundary (condition)

Do you agree with such definition?

No: A standing light wave within a cavity is standing because it experiences boundary conditions: It is definitely not a "particle".
Similarly a standing electron wave within a metal is NOT a "particle": It is a delocalised wave. Thus there are NO "charge-carriers" within a metal.

When you apply an electric-field to the metal, the boundary conditions change: The delocalised waves superpopse to form wave-packets which can transfer charge. One can of course now treat these wave packets as if they are "particles": However, they are still waves which became localised because the boundary conditions require it when applying the electric field.

Thus under suitable boundary conditions one can get localisation of waves BUT it is NOT the case for ALL boundary conditions, and the localised waves are NOT "particles". So "particle = wave with boundary (condition)" is NOT generally valid.
johanfprins
3.7 / 5 (3) Jul 05, 2010
Both! Even Einstein was forced to agree, since E=MC^2.

Don't lie: Einstein NEVER agreed. That is why he posed the EPR paradox. Neither did Schroedinger and de Broglie ever agree fully!

FTIR, AAS and EDS. AAS stands for Atomic Absorption Spectroscopy (look the other 2 up :-)

I do not have to look these techniques up since I have used them directly and indirectly during my physics-career: I cannot in my wildest dreams see how they could convince anybody with common sense that wave-particle duality is real. Are you sure you did not see the Cheshire cat within your "ground state flame"?

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