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New evidence for quantum Darwinism!

Well, what do you know.  Less than two weeks after I found out about the concept of quantum Darwinism for the first time, there’s a report of an experiment that’s actually found evidence for the process, and apparently not for the first time:


Since quantum Darwinism was first proposed in 2003 by Wojciech Zurek of Los Alamos National Laboratory, several studies have found evidence to support the idea. Most recently, a team of physicists and engineers from Arizona State University and the Naval Research Laboratory in Washington, D.C., has performed experiments using scanning gate microscopy to image scar structures in an open quantum dot. Their results have revealed the existence of periodic scar offspring states that evolve and eventually contribute to a robust state, much in the way that the derivation of pointer states is predicted by quantum Darwinism.

The “scars,” as the researchers explained, are actually scarring on the quantum wave functions, which cause the wave functions’ amplitudes to be highly concentrated along classical trajectories. Scars are traditionally thought to be unstable, where any small perturbation could break up the connection to the classical trajectory. However, when scar states replicate and evolve through quantum Darwinism, becoming a family of mother-daughter states, they can become coherent and eventually stabilize into multiple pointer states.

To detect this scar replication, the researchers used scanning gate microscopy to scan a conductive tip over the scar structures at a constant height. The tip acts as a local perturbation by causing a change in electrical conductance proportional to the sample’s electron density at that location. By measuring the change in conductance at different locations, the technique revealed that the scar structures have a periodic magnetic field that fits well with the idea of periodic offspring states.

So it sounds like this is quickly becoming more than an abstract interpretation.  There’s real evidence that this is actually going on.  This is a major step forward in explaining something that’s been a point of contention in quantum physics for generations: how the wavefunction “collapses” (or appears to) to produce our “classical” world.

I do wish they weren’t calling it “quantum Darwinism,” though.  “Darwinism” is a loaded term in a lot of ways.  It’s misapplied when used for evolutionary biology, often used by creationists to paint evolutionary theory as just blind faith in one man’s dogma, when in fact modern evolutionary biology is as far beyond Darwin’s tentative, incomplete, and often inaccurate ideas as modern physics is beyond Newton’s pre-relativistic, pre-quantum model of physics.  Darwin was just the beginning of the process.  Also, more broadly, the term “Darwinism” has long been co-opted for philosophies like social Darwinism that distort and misuse “survival of the fittest” notions (a term actually coined by Herbert Spencer) into something rather different from what Darwin had in mind.  A term like “quantum evolution” or “quantum selection” might be more appropriate, though admittedly less evocative.

On the other hand, Zurek isn’t proposing a comprehensive analogy with evolutionary biology, merely evoking the specific idea of the environment selecting for entities better adapted to thrive in that environment, which is essentially the concept of natural selection that Darwin introduced in On the Origin of Species.  So I guess this is one case where the term “Darwinism” isn’t really inaccurate, as long as you ignore the unfortunate ideological baggage attached to the term by its many abusers.

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  1. Peter
    June 4, 2010 at 4:04 pm

    What sort of implications does this have for interpretations, if any?

    • June 4, 2010 at 4:14 pm

      Well, as I understand it, QD is an explanation of the mechanism behind decoherence. It explains the appearance of wavefunction collapse in a way that requires no actual collapse. So it supports decoherence interpretations such as Everett (Many-Worlds). I think.

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