Quantum biology refers to applications of quantum mechanics and theoretical chemistry to biological objects and problems. Over the past decade, growing evidence suggests that certain biological systems might employ quantum mechanics. In recent years progress in experimental technology has revealed that quantum phenomena are relevant for fundamental biological processes such as photosynthesis, magneto-reception and olfaction.
One of the most scientifically accepted hypothesis on how some migratory birds can sense the Earth’s magnetic field is based on photochemical reactions in the birds retina. The excitement of electrons in pairs of light sensitive proteins called cryptochromes causes a physical rather than chemical signature on the proteins that the birds detect. This hypothesis explains why some migratory birds, such as the European Robins, can only orient themselves to a magnetic field in light and with a working ocular system.
Darpa’s Defense Sciences Office under its “QuBE,” short for “Quantum Effects in Biological Environments” program is looking for innovative research that will investigate the way that nature may be exploiting quantum mechanical effects in biological systems.
“Nature is an extraordinary testbed. We think it’s possible that over millions of years of evolution, biological organisms have developed systems that exploit quantum physics,” Goodman said. “The QuBE program is designed to test this hypothesis. The work we’re pursuing questions fundamental assumptions about how biological processes work.”
If manifestly quantum effects are shown to be at play in biological systems, and scientists can understand the mechanisms at work, the findings could lead to fundamentally new technologies, including bio-inspired sensors. In addition to exploring magnetic navigation, QuBE researchers are also studying photosynthesis, olfaction, and the underlying theoretical framework needed to link biology and quantum phenomena.
“The time and cost to develop many of the traditional sensors that the Department of Defense uses is substantial. Nature, on the other hand, has already evolved extraordinary capabilities—think of a dog’s sense of smell,” Goodman explained. “In addition to being extremely capable, natural sensors are also robust, durable, exhibit great sensitivity and enormous selectivity, and are produced amid the dirt and dust of the natural world; nature doesn’t need clean rooms. We’re hoping to follow nature’s lead to capture those qualities in manmade sensor systems.”
Quantum Biology Effects
However, in recent years progress in experimental technology has revealed that quantum phenomena are relevant for fundamental biological processes such as photosynthesis, magneto-reception and olfaction.
How migratory birds get directions by sensing the earth’s magnetic fields?
Magnetoreception is the ability of some migrating species to navigate using the Earth’s magnetic field. Earth’s. First, light induced electron transfer from one radical pair forming molecule (for example, in a cryptochrome in the retina of a bird) to an acceptor molecule creates a radical pair; a radical pair is (typically) a pair of bound molecules that each has an unpaired electron.
These pairs are created, by a photochemical process, in spin correlated states; that is, singlets or triplets. The state of these spins then evolves under the combined effect of the Earth’s weak magnetic field and internal nuclear hyperfine interactions with the host nuclei. Second, the singlet (S) and triplet (T) electronspin states interconvert owing to the external (Zeeman) and internal (hyperfine) magnetic couplings. The singlet and triplet radical pairs recombine into singlet and triplet products, respectively, which are biologically detectable.
In the case of the avian magnetoreception, if the interpretation of behavioural experiments on certain avian species is correct, then it could be that the ability of these species to navigate by the Earth’s magnetic field is transduced by a magnetically sensitive chemical reaction that relies on certain subtle quantum effects.
How animals and insects smell odorant molecules in the air to avoid danger or find food?
There is also quantum theory of olfaction. The vast majority of smell scientists consider that our olfactory receptors detect aspects of the molecular shape of an odour – its size, functional group and so on. However, problem is that no one has been able to show how this works, nor are we even sure exactly what is detected: is it the smell itself, or smell plus molecular chaperone, write Al-Khalili and McFadden.
In contrast to this dominant view, there have been suggestions over the years that “quantum tunnelling” in our noses is responsible, and there has been an occasionally acrimonious debate over the validity of these theories. As Al-Khalili and McFadden acknowledge, resolving this issue will involve studying the crystal structure of the receptors (this is very difficult), but they emphasise that the only theoretical explanation for our sense of smell is the quantum one
How plants harvest sunlight and turn it into electrical energy with 100% efficiency?
Photosynthesis provides energy for almost all life on Earth. This energy, in the form of photons, is absorbed by light harvesting antennas as an electronic excitation. This excitation is then transported from each antenna to a reaction centre where charge separation creates more stable forms of chemical energy. Photosynthesis, is ruled by quantum energy transfers. Energy “simultaneously samples” potential routes, and opts for the most efficient one to get the job done.
What is remarkable is the observed efficiency of this and other photosynthetic units. Almost every photon (nearly 100%) that is absorbed is successfully transferred to the reaction centre, even though the intermediate electronic excitations are very shortlived (~ 1 ns).
DARPA’s Quantum effects in Biological Environments (QuBE)
Biological sensors often display high sensitivity, selectivity, and low false alarm rates while being fabricated and operated in dirty, noisy natural environments. Attempts to emulate these sensors synthetically have not fully met expectations.
Recent evidence suggests that some biological sensors exploit nontrivial quantum mechanical effects to produce macroscopic output signals. Examples of such sensors include the highly efficient energy transfer properties of photosynthesis in plants, bacteria, and algae; magnetic field sensing used by some birds for navigation; and the ability of some animals to detect odors at the single molecule level.
The Quantum Effects in Biological Environments (QuBE) program is laying the foundation for novel sensor designs by challenging the long-held view that biological sensors utilize primarily classical physics. QuBE will verify, understand, and exploit these effects to develop new scientific foundations for sensor technologies for military applications.
Study on Magnetic Compass Orientation in Birds Builds Case for Bio-Inspired Sensors
Researchers show that migratory birds are unable to use their magnetic compass in the presence of urban electromagnetic noise. The findings open up new areas of study for magnetic sensors.
Researchers working on DARPA’s Quantum Effects in Biological Environments (QuBE) program have shown that the electromagnetic noise that permeates modern urban environments can disrupt a bird’s internal magnetic compass. The findings settle a decades-long debate into whether low-level, artificial electric and magnetic fields can affect biological processes in higher vertebrates. For DARPA, the results hint at a new class of bio-inspired sensors at the intersection of biology and quantum physics.
In an online Nature paper, research teams from the University of Oldenburg and the University of Oxford, led by Prof. Henrik Mouritsen, document a series of experiments using European robins that were carried out from 2005 to 2011.
Night-migratory songbirds like European robins have an internal magnetic compass that allows them to choose the correct migratory direction during the spring and fall migration seasons. However, when the robins used in the Oldenburg experiments were exposed to everyday levels of electromagnetic background noise, the birds failed to orient themselves correctly. When the researchers later shielded the birds from background electromagnetic noise, the birds oriented to the correct migratory direction. Birds tested in rural environments, far from sources of electromagnetic noise, required no screening to properly orient using their magnetic compass. Full details of the experiments are available in the paper.
Electromagnetic noise is emitted everywhere that humans use electronic devices. The observations from the Oldenburg study suggest that birds utilize a biological system that is sensitive to manmade electromagnetic noise with intensities well below the guidelines for human exposure adopted by the World Health Organization.
But why is DARPA studying bird migration? According to Dr. Matt Goodman, the Program Manager for QuBE, one reason is that the observed phenomena might have their roots in quantum physics.