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Groundbreaking Quantum Light Experiment Validates Single Photon as the Initiation of Photosynthesis

Scientists have used quantum technology to track individual particles of light as they begin the process of photosynthesis.

The intricate process of photosynthesis, which fuels much of life on Earth, has now been demonstrated to commence with the influence of just a single photon. Scientists have long suspected the sensitivity of photosynthesis to individual photons, considering the relatively sparse nature of sunlight at the cellular level of plants. However, it is only through the utilization of quantum physics that researchers have been able to witness the initiation of this process by a solitary packet of light in an experiment detailed in the journal Nature on June 14.

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

The ability to measure the requirement of only one photon for photosynthesis represents a groundbreaking achievement, as noted by Sara Massey, a physical chemist at Southwestern University in Texas, who was not involved in the research. Massey emphasizes the value of tangible data obtained from such experiments in verifying this notion firsthand.

The experiment faced a significant challenge due to the inherent difficulty in generating single photons. To address this, the researchers generated pairs of entangled photons, which exhibited interdependent behavior regardless of their physical separation, as dictated by the laws of the quantum realm. One photon from each entangled pair was directed towards a detector to confirm the presence of only its corresponding photon within the system. Simultaneously, the matching photon was directed into the light-harvesting 2 (LH2) complex of a bacterium, which plays a crucial role in the initial step of photosynthesis. The LH2 complex, extracted from the purple bacterium Rhodobacter sphaeroides, absorbed light energy and transferred it to the photosynthetic machinery. In the experimental setup, the LH2 complex emitted light after absorbing the energy, indicating the successful passage of the photon through the system.

Graham Fleming, a physical chemist at the University of California, Berkeley, and Lawrence Berkeley National Laboratory, and co-author of the study, explained the process: “We create a pair of entangled photons, detect one (the herald), and then expose the other one to our sample while observing for a signal.”

However, the practical implementation faced difficulties due to fluorescence occurring in multiple directions, making it challenging for conventional detectors with limited fields of view to capture the signal. Fleming acknowledged the complexity, stating that detecting the fluorescence was considerably more challenging compared to detecting the herald. Nonetheless, the scientists persevered, repeating the process numerous times, producing over 17 billion herald photons, and successfully detecting LH2 fluorescence in approximately one out of every 10,000 heralds. This extensive repetition enabled statistical analysis of the results. Quanwei Li, a quantum physicist at U.C. Berkeley and co-author of the study, highlighted the significance of this step in quantum optics, given the delicate nature of individual photons. The analysis confirmed that both the input and output of the experiment involved single quanta of energy.

Jianshu Cao, a physical chemist at the Massachusetts Institute of Technology who was not involved in the research, hailed the use of quantum light in demonstrating the quantum nature of energy absorption occurring one photon at a time. Cao expressed intrigue regarding the application of new quantum technology to the intricate and complex biological system of photosynthesis.

The success of this experiment opens doors for future investigations utilizing quantum light, not only within the realm of photosynthesis but also in other areas of study. The research provides an unprecedented level of insight into a process fundamental to life on Earth. Massey reflects on the significance of zooming in at such a minute level, highlighting the experiment’s ability to examine a single particle of light, which is both remarkable and mind-boggling.

Reference: Scientific American


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