Experiment investigates how classical physics may emerge from quantum physics

May 24, 2013 by Lisa Zyga feature
Illustration of the simple quantum system consisting of two incommensurate optical lattices that “kick” a macroscopic atomic matter wave (an optically trapped Bose-Einstein condensate). The researchers found that classical behavior emerges naturally in this closed quantum system. Credit: Bryce Gadway, et al.

(Phys.org) —In order to better understand how the laws governing the quantum and classical regimes are related to one another, physicists have performed an experiment allowing them to observe a quantum-to-classical transition in a simple closed quantum system. The results suggest that classical behavior may be an innate property of certain isolated quantum systems such as the one studied here, and can emerge from quantum physics under certain conditions.

The physicists, Bryce Gadway, et al., led by Professor Dominik Schneble at Stony Brook University in New York, have published their paper on the quantum-to-classical transition experiment in a recent issue of Physical Review Letters. Gadway is currently at the University of Colorado in Boulder.

"Our results suggest that may emerge in a very natural way in large —in this case, 'large' meaning just two coupled subsystems—without the invocation of an external 'environment' responsible for decoherence," Gadway told Phys.org. "These results are certainly suggestive that classical behavior—specifically diffusive random-walk-like transport at the expected classical rate—is an innate property of this simple, quantum chaotic system."

The scientists' observation confirms a prediction from 1988 by S. Adachi, et al., that classical behavior will emerge in a driven quantum system consisting of two coupled kicked rotors. In the new study, the researchers realized the kicked rotors by "kicking" a macroscopic atomic matter wave (an optically trapped Bose-Einstein condensate) with two periodically pulsed . By spacing the pulses a certain way, the researchers could create coupling between the two optical lattices, which act as the rotors.

The physicists found that the system's momentum is affected differently when kicked by two coupled rotors compared with being kicked by a single rotor. Specifically, coupling causes a transition from localization to delocalization. In this context, localization means that the matter wave does not diffuse, or spread. On the other hand, delocalization corresponds to the emergence of classical diffusion, as well as fully chaotic behavior. Essentially, the coupling of the two kicked rotors results in a localization-to-delocalization transition, signaling a quantum-to-classical transition, just as predicted 25 years ago.

Although other demonstrations of quantum-to-classical transitions have been previously reported, the researchers explain that this demonstration is particularly interesting because it occurs in a closed system.

(a) Illustration of a Bose-Einstein condensate exposed to a series of pulses from two incommensurate optical lattices that act as kicked rotors. (b) Diffraction spectra of atoms released after 1 kick and 40 kicks, when driven with a single lattice. The graph shows the momentum distribution after 40 kicks. (c) As in (b), but for driving with two lattices. The dashed black line in the graph at the bottom is a Gaussian profile corresponding to diffusive spreading, which signals classical behavior. Credit: Bryce Gadway, et al. ©2013 American Physical Society

"Thus far, most demonstrations of a quantum-to-classical transition have taken place in open quantum systems, where a purely quantum mechanical subsystem (such as a qubit) is coupled to some macroscopic reservoir, with the end result being decoherence of the pure subsystem," Gadway said. "This is somewhat artificial because it relies on divorcing the reservoir from the system that decoheres; it assumes that information lost to the reservoir will never be returned.

"What we've been able to show is that such quantum-to-classical transitions can emerge even in the dynamics of simple closed quantum systems. By coupling two quantum chaotic subsystems—so-called 'kicked quantum rotors'—they both go from being localized due to destructive interference to displaying diffusive energy transport in a completely classical fashion. This is despite that the fact that all the dynamics are strictly unitary and time-reversible."

In the future, the hope that the experiment can be extended to three or more coupled rotors using additional optical lattices. As Gadway explained, these experiments and others could provide further insight into the transition from to delocalization in nonlinear, disordered quantum systems.

"One future line of investigation would be to simply scale this up to coupling three or more quantum kicked rotors, where we expect that the transition to classical behavior may happen for weaker driving and/or weaker rotor-rotor coupling," he said. "We are also looking to couple the external motion of these particles to their internal states (i.e., their spin) to study quantum chaos in 'spinful' systems."

Explore further: Competition in the quantum world

More information: Bryce Gadway, et al. "Evidence for a Quantum-to-Classical Transition in a Pair of Coupled Quantum Rotors." PRL 110, 190401 (2013). DOI: 10.1103/PhysRevLett.110.190401

Professor Dominik Schneble's webpage: Ultracold Physics at Stony Brook University

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User comments : 29

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indio007
1.4 / 5 (9) May 24, 2013
Have we fallen so far that tweaking a mathematical model is called an experiment?
drhoo
not rated yet May 24, 2013
""Have we fallen so far that tweaking a mathematical model is called an experiment?""

monte carlo simulation ??
indio007
1 / 5 (6) May 24, 2013
http://quantummec...157.html

Quantum rotors don't actually exist.
ValeriaT
1 / 5 (14) May 24, 2013
Experiment investigates how classical physics may emerge from quantum physics
Thanks to Couder and dense aether model we already know, how the quantum physics emerges from classical physics.
EyeNStein
1 / 5 (10) May 24, 2013
For quantum and classical you can also read as wavefunction and particle behaviour while reading this article.
What we have here is a glimpse at the boundaries between, and nature of, wave particle duality.
EyeNStein
1.3 / 5 (11) May 24, 2013
The two optical confinement grids relationship, or lack of relationship, these experimenters haver created are simulating coherent and non-coherent environments. In one the wavefunction can persist and in the other de-coherence occurs and classical particle behaviour appears.
If the double slit experiment could be performed between these laser grids: In one case it would be the same as in free space (coupled grids); and in the other pure particle behaviour would be observed (with the two similar but not spacially or temporally related grids).
We have created or destroyed a form of experimental artificial entanglement between the two grids! This is a whole new window on the basis of existence.
EyeNStein
1 / 5 (9) May 24, 2013
Never before have we been able to destroy and create a quantum entangled situation, only destroy them and measure the debris.
kochevnik
1 / 5 (7) May 24, 2013
http://quantummec...157.html

Quantum rotors don't actually exist.
Neither do you, but there you are
EyeNStein
1 / 5 (9) May 25, 2013
Specifically, coupling causes a transition from localization to delocalization

This controlled transition from particle --to -- space filling wavefunction behaviours is unique in its controllability in any experiment I've heard of.
Who would have thought that two totally synthetic laser grids could either appear quantum coherent or quantum decoherent to BEC particles just by altering their artificial time and space relationships?
Reagan
1.7 / 5 (12) May 25, 2013
i am new here .... i love this site ...
Reagan
1.4 / 5 (11) May 25, 2013
The physicists, Bryce Gadway, et al., from Stony Brook University in New York...... great....

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check this site home tab.
DUB30.com
EyeNStein
1 / 5 (8) May 25, 2013
This experiment could be the 'Brownian motion' unexpected hint of breakthrough of understanding quantum physics.
Or on the other hand:They may have just used a QUANTUM method to couple their two independent laser grids, in which case any laser photon's wavefunction would be entangled in either/both grids simultaneously and this result isn't special or unexpected at all.
EyeNStein
1.7 / 5 (11) May 25, 2013
You do know that "dub30.com" is a scam right??
yogurtforthesoul
1 / 5 (5) May 25, 2013

If the double slit experiment could be performed between...


I'll have to think about just how exactly I want to say it, but it seems like this could be an alternate path to check or do the double-slit experiment in a far different setting. I have to wait, because right now the idea is very incomplete.

I just know that while I was reading the article I got the sudden and distinct feeling that particle/waveform duality issues might be looked at "again" via this methodology with a lot of tinkering of course. I'll try to post back with the full idea before I'm spammed to death with miscellaneous one out of five.

BTW, this is nothing radical, just another way to further the same test (NOT a replacement--though I'd like to see a VERY heavy duty quantum mechanical version of the double-slit done one day, but that is a bit off in the future due to our technological limitations).

So, mark down my next post instead of this one, until I find a way to say what I need to correctly.
LarryD
1 / 5 (4) May 25, 2013
Hey, EyeNStein...no I'm not stalking you ha!...You and a couple of other guys sound reasonable enough on this site and obviously much more knowledgeable than me on these matters. So...here's my problem. To me it sounds like just a matter of Logic that QM and CM should meet at some juncture simply because we understand that both exist. Everything Macro is a product/consequence of QM (the other way round if one favours Biocentrism). I have always thought that chemical reactions were one particular route to finding that 'phase' where CM arrives because of QM...that is, those reactions that reveal a macro aspect (dropping a lump of Sdium in water for example). Wouldn't studies on the QChem level have more chance of revealing the '?' in Qm-?-CM in question? I find that discussing |x>+|x'>.....doesn't help me very much.
ValeriaT
1 / 5 (8) May 25, 2013
It's not indeed true, that the classical physics emerges from quantum physics (it's a portion of mainstream physics propaganda be more specific). The quantum physics is not even extraordinarily faithful description of reality - it must be mixed with special relativity (in Dirac equation and similar) to work better. And many theorems (Hamiltonian mechanics) of quantum mechanics are actually a classical physics theorems. In AWT the behavior of random particle gas is still most trivial and fundamental physical system requiring the least number of postulates to work. The quantum mechanics corresponds the perspective of observation of water surface with its own ripples at small distance scale, where everything gets blurred with Brownian noise and the density of environment is proportional to its energy density in accordance to E=mv^2 equivalence.
LarryD
1 / 5 (3) May 25, 2013
Not sure that I agree in total, with you ValeriaT. I am in the process of making myself more familiar with AWT-like theories so until I gather at least some knowledge of your perspective I can't really argue with you.
My basic argument comes simply from a logical progression from one state to another and I make the distinction that I can touch, feel etc whatever is locally macro but it takes my brain to interpret the signals via sound (atoms) and photons that enter my eyes, or say some 'plasma' that causes pain (fire). But I can't actually manipulate these on the macro scale to examine them
EyeNStein
1 / 5 (8) May 25, 2013
@LarryD: there is very little that is intuitive about QM, which is why it took geniuses like Einstein, Dirac and Feynman and a lot of unsung mathematicians to create the mathematical descriptions of reality (Relativity, QED and Standard model) we have today.
Most of the arguments you will read in the comments are about how to interpret and understand the reality those equations represent. (Though some 'contributors' disagree with it all and point you at their favourite fringe theory website, even if it disagrees with observed experiment as described in the article .)
EyeNStein
1 / 5 (8) May 25, 2013
@LarryD: As for accessing quantum theory via chemistry, it's probably the least direct path: Though as we investigate biology in depth we find that nature has found ways to exploit quantum effects to create colours and access difficult reactions which we can learn useful quantum principles for chemistry from.
Even the yellow colour of gold is a quantum effect we can investigate and learn from.
Nano-scale chemistry and physics are especially dependent on quantum effects, and creating substances on the nano scale often requires chemical knowledge.
ValeriaT
1 / 5 (8) May 25, 2013
The whole point is in Occam criterion. At the moment, when the behavior of quantum system can be modeled with classical particle systems in its entirety, then the classical physics becomes more fundamental, because it requires lower number of ad-hoced assumptions (i.e. postulates) for its reasoning. It's simpler, but more flexible and general model of reality.
KBK
1 / 5 (8) May 25, 2013
Important note to article writer:

Stop using the word law to talk about theories and postulates.

Law is a human societal concern, and it has to do with punishment for people doing things you, in the form of group consensus -deem socially unacceptable.

It has no place, whatsoever, in the world of science or physics. It's use in the world of physics and science is totally against the so called reasons behind the very basis of science. It is an insult and ignorance of the most fundamental kind.

Leave the word law to the ignorant and the overtly religious who push their desires and emotions into other people.
ValeriaT
1 / 5 (8) May 25, 2013
Law is a human societal concern.. It has no place, whatsoever, in the world of science or physics
You would be surprised, how deeply the (scopes of) physical laws are defined with intersubjective agreement of people involved. For example, in laws (rules or postulates) of special relativity the speed of light is constant. But we know from gravitational lensing, that the speed of light is changing often. In these situations the relativists are using to say, it's the space-time, which is curved here - not the path of light. But this is solely arbitrary stance invented into behalf of abstract relativity theory, because many astronomers are still using the gravitational lenses like any other material lenses in their observations. There is actually no objective criterion developed for it yet.
LarryD
1 / 5 (4) May 25, 2013
EyeNStein, appreciate your reply and understand. Have read much about the nanoscale investigations (such as the Gold being used in various applications) and now remember that not all of the applications were fully understood. This suggests that, as you say, something more fundamental is at work here. All good stuff eh? Thanks again.
With regard to the comment above regarding the use of the word 'law' I would suggest KBK is incorrect. 'Law' is a 'barrier' which is applicable to any topic but it does have a double meaning. It implies a consequence if 'broken' in the social application but has a sense on something being 'constant' in other areas. The 'law of gravity' is not just a 'postulate' because it has the constant consequence of keeping you on the ground. So don't bring religion etc into the scientific discussion, please, and don't deny the scientist the use of the English language...thank you.
YawningDog
4 / 5 (4) May 26, 2013
Who are the idiots who gave "Reagan" so many stars.

"i am new here .... i love this site ..." Doesn't your mommy love you any more? Report the spam, don't get sucked into his b.s.
dedereu
1 / 5 (5) May 26, 2013
This interesting experiment on destructive interferences does not solve in any wxay the basic problem of quantum mechanics : how we pass from the possibility of many parrallel configurations evolving at the same time ( particules at many place at the same time ) to a single unique classical configuration (particules at a single place), among the many possible configurations, separated by theses destructive chaotic interferences of the wave function, which look like many small parallel micro-worlds, for a micro-system isolated from our external world.
If it was possible to comme back from theses classical worlds, by reversing the movement with very high precision, this would prove that theses parallel worlds are real and not lost, and prove that we live in one world of the many parallel worlds of the quantum mechanic wavefunction.
dedereu
1 / 5 (6) May 26, 2013
As already explained by Dutch, in the 1980,, the realization of an, efficient real quantum computer, which, in this experiment, is, equivalent to coming back to quantum, by reversing the movement, from the apparent classical state (with sufficient precision to keep intact the phases correlations between the many parallel apparent classical states for a resurrection of the quantum state), will prove the reality of the existence of many parallel worlds with different histories, in our universe, without being able to explore them, as it is written in our quantum equations with many parallel histories. It is a very difficult experiment with very fondamental consequences for the understanding of our universe (more exactly our many parallel universes)
ValeriaT
1 / 5 (7) May 26, 2013
... system consisting of two coupled, kicked quantum rotors, by subjecting a coherent atomic matter wave to two periodically pulsed, incommensurate optical lattices. Momentum transport in this system is found to be radically different from that in a single kicked rotor, with a breakdown of dynamical localization and the emergence of classical diffusion..


So that these guys realized, when they constrain pair of quantum oscillators with classical boundary conditions (periodic optical lattice, harmonic vibrations), then it's not undulating like the single unconstrained quantum oscillator anymore. Isn't it a little bit trivial conclusion? What else we should expect? Don't we known that the higher number of quantum oscillators are coupled mutually, the more classical behavior we get? Not to say inside of harmonic optical lattice, which is classical by its whole definition?
RichManJoe
1 / 5 (5) Jun 11, 2013
I am a firm believer that quantum effects directly influence the macro world. As proof, whenever I look for a tool in my tool bag, it is where I look last. When I start looking at the top, it is on the bottom. And when I try to trick it by first looking in the bottom, it is riding on the top.
LarryD
1 / 5 (1) Jun 11, 2013
RichManJoe, or maybe you're just changing from one time line to another...if you believe that, that is. But I know the feeling well and dejavue too...

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