As far as science was concerned, quantum states and quantum effects were observable (if at all) only in the deepest cold, in temperatures hovering just above absolute zero. There were moments of research during and after the 1990’s when quantum effects were managed more than a few degrees (Kelvin) off zero, but for all practical purposes “cryo” and “quantum” were believed to be exclusively copacetic. Then around 2000 new research began discovering quantum effects in a most unexpected quarter – biology – and at ‘normal’ or so called room temperatures. This is seemingly impossible, however, apparently true.
[SciTechStory: Confirmation: Quantum entanglement in photosynthesis]
[SciTechStory: The robin flies with quantum coherence]
From bird navigation to photosynthesis the evidence is mounting that quantum effects, especially quantum coherence, are used in biological processes, and most astonishingly, the effects persist in functioning at biologically sustainable temperatures. While biologists are thrilled by this discovery and for them it opens a new world of research, called quantum biology, for physicists it is also a massive conundrum. How is this persistence of quantum states at high temperatures possible?
There are attempts to answer that question, the newest just hitting the Net at arXiv [29 February 2012, Open Access, Quantum biology on the edge of quantum chaos] by a trio of physicists, Gabor Vattay and Stuart Kauffman and the University of Vermont (USA) and Samuli Niiranen at the Tampere Institute of Technology (Finland). They believe they have found a mechanism that explains how quantum coherence is maintained at biological temperatures.
The heart of their theory is that biological persistence of quantum effects depends on the existence of what is called state transition. The most intuitive of these transition states is where water goes through phases between solid (ice), liquid (water) and gas (water vapor).
The transitions the researchers consider a template are more subtle (atomic rather than physical) – the metal to insulator transition (MIT). There are various materials, especially semiconductors (as the name implies) that with a little nudge (chemical or electrical, for example) can conduct electrons (conductor), or not (insulator). In the technical terms of the paper, the quantum process they are describing is a metal-insulator transition from Anderson localization to extended wave functions. (Where waves of energy remain ordered, coherent, and then transition to disordered wave functions. During this transition a semiconductor changes from an insulator with ordered electro-magnetic wave functions to a metal (conductor) with disordered wave functions.)
Here’s where their story becomes even more difficult to follow. I’ll do my best to keep it simple, but that means losing precision: At an even more subtle level are the quantum effects, especially quantum coherence where particles such as photons, electrons or even molecules are said to be ‘entangled,’ which in quantum-speak is where pairs of particles are, in effect, identical (share the same state). Measure one particle of the pair and you know everything about the other particle (called quantum superposition). The transition in this realm is based on moving to and from quantum coherence to quantum chaos (where the particles are no longer entangled).
In the previous world of quantum mechanics, at least in the research lab, a state of quantum coherence is incredibly fleeting, measured in nano or micro seconds. Quantum coherence ‘normally’ decoheres (breaks down) very rapidly, and at higher temperatures can’t be created (in the lab) at all. Yet nature seems to do it – continually and at high temperatures. Here’s where the new theory steps in and maintains that in photosynthesis, for example, the transition state between quantum coherence and chaos is maintained by the continual addition of new particles – photons of sunlight. In a system they tested, using the light-collecting components of plants called chromophores; they were able to show that loss of quantum coherence is significantly delayed and rebuilt by trapping (harvesting) incoming photons. The researchers call it the “Poised Realm” between the coherent (quantum mechanics) and incoherent (classical mechanics) world.
What is this all about? The key to an answer, at least in the case of photosynthesis, is that the quantum effect involved is part of the ‘harvesting mechanism’ that converts sunlight (photons) into stored energy (as carbohydrate). In short, it is one of the fundaments of life.
What Vattay, Kauffmann and Niiranen have done is work out a model (in mathematics, of course) that they have been able to demonstrate with a biological experiment that explains the quantum mechanism behind this process. They believe that their model can eventually explain many if not all occurrences of quantum biology. The implications are vast, for example, as they put it: “Using this new critical design principle from biology might open the way to build lossless quantum coherent energy and information processing devices operating at room temperature.”
That remains to be seen, of course. Their paper presents a theory and minimum experimental evidence. It will now undergo what all challenging theories experience – critique and attempts to re-create the original experiment along with any number of new experiments to test the theory. In a few years, more will be known about how robust their theory actually is. In the meantime, it at least shows that plausible explanations can be found for something that up to now were considered unexplainable. That’s called progress in science.