Over the course of an experiment involving the quantum entanglement of photons produced from naturally-occurring bioluminescent material, a team of researchers from Northwestern University has discovered that the special structure of proteins that were part of the bio-material somehow protected the photons’ quantum state from being disrupted. Typically, quantum states generated in the lab are very fragile, and researchers go to great lengths to ensure that the particles they’re studying aren’t affected by external forces before they have a chance to measure their properties.
"Can we apply quantum tools to learn about biology?" This question was asked by Prem Kumar, a professor of electrical engineering and computer science in Northwestern’s McCormick School of Engineering and of physics and astronomy. "People have asked this question for many, many years — dating back to the dawn of quantum mechanics," referring to a similar curiosity held by quantum physics pioneer Erwin Schrödinger earlier in the twentieth century. "The reason we are interested in these new quantum states is because they allow applications that are otherwise impossible."
Amongst those applications is the phenomenon of quantum entanglement, involving the instantaneous influence that two paired particles can have over one another: while entangled, an effect on one particle is mirrored by its twin instantaneously, regardless of how far apart the two particles are. This instantaneous transference of information is an important factor in the development of quantum communications technologies, such as quantum computers. The entangled state, however, can be easily disrupted by factors stemming from the local environment, forcing researchers to isolate them to maintain their special state.
For their experiment, Kumar’s team made use of photons emitted from green fluorescent proteins, commonly found in bioluminescent material, such as that found in glowing jellyfish, and has also become increasingly useful in biomedical research. The entanglement property they focused on is called "polarization entanglement", where the wave portion of each of the entangled pairs of photons had the same polarity.
While they found that the entangled photons were still vulnerable to having their states disrupted when being measured, they found that "the prepared state is less sensitive to environmental decoherence because of the protective beta-barrel structure that encapsulates the fluorophore in the protein." That is, the special, barrel-shaped protein structure surrounding each of the molecules that emit the light (the fluorophores) somehow preserved their quantum state, making the light source less likely to be disrupted by the external environment.
Kumar’s team suggests that this property could provide a stable source of entangled photons for use in "biomimetic quantum networks" — quantum networks that mimic biological systems, or quantum sensor applications. The presence of beta-barrel protein structures, named for their distinctive barrel shape, are also not unique to green fluorescent proteins, and are used extensively throughout our biological processes — perhaps future discoveries may yield links to other quantum properties found within ourselves.