NATURE
International Weekly Journal of Science
Volume 330 | Issue 6146 | 26 November 1987
LETTERS TO NATURE
Evidence for Quantum Coherence in Photosynthetic Energy Transfer
H.C. Voss¹, P.J. Engel², G.R. Fleming³
¹Department of Chemistry, University of Surrey, Guildford, UK ²Department of Physics, University of Surrey, Guildford, UK ³Department of Chemistry, University of California, Berkeley, USA
Abstract. We present spectroscopic evidence suggesting quantum coherent energy transfer in photosynthetic light-harvesting complexes at physiological temperatures. Two-dimensional photon echo spectroscopy of the Fenna-Matthews-Olson (FMO) complex reveals long-lasting quantum beating at 77 K, indicating electronic coherence times exceeding 660 femtoseconds. At room temperature (300 K), coherence persists for approximately 300 fs—orders of magnitude longer than predicted by classical models. These observations challenge conventional descriptions of biological energy transfer and suggest that quantum mechanical effects may play a functional role in photosynthesis.
Introduction.
The mechanism of energy transfer in photosynthetic complexes has been described as an incoherent hopping process governed by Förster theory¹. However, recent theoretical work has suggested that quantum coherence between electronic states may enhance transfer efficiency². We report experimental observation of coherent electronic oscillations in the FMO complex from Chlorobium tepidum using two-dimensional electronic spectroscopy (2DES).
Methods.
Samples were prepared as described previouslyÂł. 2DES experiments employed 20 fs pulses centered at 800 nm. Coherence dynamics were extracted from the waiting-time evolution of cross-peak amplitudes.
Results.
Figure 1 shows oscillatory signals in the 2D spectrum at waiting times from 0 to 660 fs. Fourier analysis reveals a dominant frequency component at [REDACTED - CLASSIFIED] Hz, with additional peaks at harmonic intervals. The coherence decay time of ~660 fs at 77 K exceeds the predicted 10-100 fs timescale for protein-induced dephasing.
[FIGURE 1: 2D photon echo spectra showing coherent beating at indicated waiting times]
Discussion.
The observed coherence times suggest that the protein environment protects electronic quantum states rather than destroying them. This implies that photosynthetic systems may have evolved to exploit quantum mechanics for efficient energy transfer—a principle we term “quantum biological optimization.”
The [REDACTED] frequency component appears to represent a fundamental resonance in the energy landscape. Further investigation is warranted to determine its biological significance.
Conclusion.
These results demonstrate that quantum coherence can persist in biological systems at physiological temperatures. The implications extend beyond photosynthesis to fundamental questions about the role of quantum mechanics in life processes.
Received: 15 October 1987 | Accepted: 3 November 1987
References
- Förster, T. Ann. Physik 2, 55-75 (1948)
- Engel, G.S. et al. Nature 446, 782-786 (2007) — [NOTE: Future citation, error in timeline]
- Fleming, G.R. & van Grondelle, R. J. Phys. Chem. 108, 79-82 (2004)
EDITORIAL NOTE
The authors wish to acknowledge the support of the Science and Engineering Research Council (UK) and the U.S. Department of Energy. A patent application has been filed regarding the [REDACTED] frequency component and its potential applications. Correspondence should be addressed to H.C. Voss at the University of Surrey.
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© 1987 Nature Publishing Group
[REDACTED SECTION - REQUIRES SECURITY CLEARANCE]
The following section has been removed by order of the Ministry of Defence:
Pages 438-442: Appendix B - Frequency Analysis and Harmonic Relationships
Pages 443-445: Materials and Methods - Spectrometer Calibration Procedures
Appendix C has been classified TOP SECRET and transferred to DSTL Porton Down.
Document reconstructed from declassified materials, 2027.