Regenerative quantum coherence in photosynthesis under natural conditions

Charles Q. Choi

Sergei Vladimirovich Kozyrev, Igor Vasil'evich Volovich

Nicolai G. Basov, Arkadii Z Grasyuk, Iosif G. Zubarev

Yiteng Zhang

We humans always want to believe that we can overpower nature. However, the reality is that nature outperforms humans in many aspects. Animals' abilities to navigate/orient and photosynthesis are two excellent examples in these aspects. However, the mechanisms underlying them are still unknown. For decades, scientists and researchers have made a lot of efforts to reveal these mysteries in nature. Recently, quantum coherence and entanglement are believed to play a crucial role in such biological systems–avian compass and photosynthesis. Thus, nature might know more tricks to utilize quantum mechanics than humans. Studies on the mechanisms underlying avian compass and photosynthesis are highly able to improve or inspire new technologies in detection of weak magnetic fields and solar cells. In this thesis, the effect of quantum coherence and entanglement in these systems is studied. Based on the studied systems, this thesis falls into two parts: avian compass–radical pair mechanism and photosynthesis–enhancing photocell efficiency via coherence. The radical pair mechanism used to explain the avian compass is studied in the first part. It is demonstrated that Cryptochrome is a suitable candidate of the primary magnetoreceptor, located in birds' eyes. Also, the product yields due to the radical pair reactions are able to act as the direction signal for birds. The long-lived quantum entanglement has presented between the radical pairs. In photosynthesis, quantum coherence has been demonstrated to play an essential role in high energy conversion efficiency. Studies have revealed that the quantum coherence can break the detailed balance, the key factor limiting the efficiency in artificial solar cells. By mimicking photosynthetic complexes, a designed solar cell taking advantage of coherent donors caused by dipole-dipole interactions is able to achieve a higher energy conversion efficiency than the famous Shockley-Queisser limit. Again, more and more evidence has shown that quantum mechanics is able to play a crucial role in biological systems. Quantum coherence and entanglement, as main signatures of quantum mechanics, can be used to explain many astonishing phenomena in nature, such as avian magnetoreception and photosynthesis. Learning from nature can accelerate developments of new technologies.

Stephan Hoyer

Ultrafast spectroscopy experiments show that photosynthetic systems can preserve quantum beats in the process of electronic energy transfer between pigments, even at room temperature. But what does this discovery imply for biology - and for quantum mechanics? This dissertation examines photosynthesis through the tools of quantum information science. We evaluate to what extent photosynthesis can be thought of as a type of quantum technology, and consider how we can apply experimental tools widely used for quantum technologies (state tomography and coherent control) to photosynthesis. Throughout, we use the Fenna-Matthews-Olson (FMO) complex of greens sulfur bacteria as a model photosynthetic pigment-protein complex.In Part I, we evaluate two mechanisms for the possible biological relevance of quantum coherent motion. First, we consider the extent to which dynamics in light-harvesting systems exhibit the quantum speedups characteristic of quantum algorithms and quantum walks. Second, we demonstrate a ratchet effect in electronic energy transfer enabled by partially coherent dynamics. To do so, we build a new model of energy transfer between weakly coupled light-harvesting complexes to understand how electronic coherence arises under natural conditions.In Part II, we present proposals for experimental probes of light harvesting dynamics with ultrafast spectroscopy. We show how the signal from pump-probe spectroscopy can be formally inverted to determine the excited state electronic density matrix. Finally, we examine the feasiblity of coherent control experiments on light-harvesting systems, and provide two realistic targets feasible with present-day technology.

Omar Gamel, C. H. Herman Chan, Graham R. Fleming +1 more