Groundbreaking Quantum Light Experiment Confirms Single Photon as the Initiator of Photosynthesis

Scientists Utilize Quantum Technology to Monitor Individual Light Particles Initiating Photosynthesis

The phenomenon of photosynthesis, which powers a significant portion of life on Earth, has been observed at the quantum level, where it has been discovered that a single photon is sufficient to initiate the process.

An artist’s depiction of plants beginning the process of photosynthesis. Credit: Jenny Nuss/Berkeley Lab

For a long time, scientists have suspected that photosynthesis is responsive to individual photons, the basic units of light, due to the relatively low intensity of sunlight at the cellular level. However, it is only with the aid of quantum physics that researchers have been able to witness the initiation of photosynthesis by a single packet of light. The findings of this experiment were published on June 14 in the journal Nature.

Sara Massey, a physical chemist at Southwestern University in Texas who was not involved in the research, describes the achievement as groundbreaking, stating, “It makes sense that photosynthesis only requires a single photon, but to actually be able to measure that… is really groundbreaking. Being able to actually see that hands-on with the data from these experiments is very valuable.”

One of the main challenges lies in the difficulty of generating one photon at a time. To overcome this obstacle, the researchers generated pairs of entangled photons that interacted regardless of their separation, as dictated by the laws governing the quantum realm. One photon from each pair was directed towards a detector to confirm that only its corresponding photon was present in the system. Simultaneously, the matching photon was sent into the light-harvesting 2 (LH2) complex of a bacterium, which plays a crucial role in the initial stage of photosynthesis. The LH2 structure was extracted from the purple bacterium Rhodobacter sphaeroides, where it absorbed light energy and transferred it to the photosynthesis machinery. When the photon passed through the system, the LH2 complex emitted light, indicating its successful passage.

Graham Fleming, a physical chemist at the University of California, Berkeley, and Lawrence Berkeley National Laboratory, and a co-author of the study, explains the experimental process: “We make a pair of entangled photons, we detect one—we call that the herald—then we put the other one on our sample and look for a signal.”

However, in practice, detecting the fluorescence is more challenging since it can occur in any direction, making it difficult for conventional detectors with limited fields of view to capture. Fleming explains, “It’s easy enough to detect the herald; it’s a heck of a lot harder to detect the fluorescence. Most of the time, we’re not seeing anything.”

Therefore, the scientists repeated the process numerous times, generating over 17 billion herald photons and detecting LH2 fluorescence in about one out of every 10,000 heralds. This extensive repetition allowed the researchers to statistically analyze the results. Quanwei Li, a quantum physicist at U.C. Berkeley and co-author of the study, emphasizes the significance of this step in quantum optics, given the intricate nature of individual photons. The analysis confirmed that both the input and output of the experiment consisted of single units of energy.

Jianshu Cao, a physical chemist at the Massachusetts Institute of Technology who was not involved in the research, commends the application of new quantum technology, particularly quantum light, to a complex and intricate biological system. Cao states, “They actually use quantum light to show that the energy absorption is a quantum event that occurs one photon at a time. I think it’s very intriguing they were able to apply the new quantum technology, which is the quantum light, to a very large and complex and messy biological system.”

According to Fleming, Cao, and Massey, the groundbreaking outcomes of the experiment open doors for future studies utilizing quantum light, not only in the realm of photosynthesis but also in broader investigations.

Furthermore, the recent research provides scientists with an unprecedented level of insight into a fundamental process essential for life on our planet. Massey expresses astonishment at the remarkable nature of the experiment, stating, “This is an experiment where you’re actually looking at one single particle of light, and that’s just amazing and mind-blowing to think about, that we’re zooming in at that level.”

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