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2 - Open quantum system approaches to biological systems
- from Part I - Introduction
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- By Alireza Shabani, University of California, Masoud Mohseni, Google, Seogjoo Jang, University of New York, Akihito Ishizaki, University of California Berkeley, Martin Plenio, Universität Ulm, Patrick Rebentrost, Harvard University, Alan Aspuru-Guzik, Harvard University, Jianshu Cao, Massachusetts Institute of Technology, Seth Lloyd, Massachusetts Institute of Technology, Robert Silbey, Massachusetts Institute of Technology
- Edited by Masoud Mohseni, Yasser Omar, Gregory S. Engel, University of Chicago, Martin B. Plenio, Universität Ulm, Germany
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- Book:
- Quantum Effects in Biology
- Published online:
- 05 August 2014
- Print publication:
- 07 August 2014, pp 14-52
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Summary
Quantum biology, as introduced in the previous chapter, mainly studies the dynamical influence of quantum effects in biological systems. In processes such as exciton transport in photosynthetic complexes, radical pair spin dynamics in magnetoreception, and photo-induced retinal isomerization in the rhodopsin protein, a quantum description is a necessity rather than an option. The quantum modelling of biological processes is not limited to solving the Schrödinger equation for an isolated molecular structure. Natural systems are open to the exchange of particles, energy or information with their surrounding environments that often have complex structures. Therefore the theory of open quantum systems plays a key role in dynamical modelling of quantum-biological systems. Research in quantum biology and open quantum system theory have found a bilateral relationship. Quantum biology employs open quantum system methods to a great extent while serving as a new paradigm for development of advanced formalisms for non-equilibrium biological processes.
In this chapter, we overview the basic concepts of quantum mechanics and approaches to open quantum system (or decoherence) dynamics. Here, we do not intend to discuss all aspects of about a century-old theory of open quantum systems that dates back to the original work of Paul Dirac on atomic radiative emission and absorption (Dirac, 1927). Instead, we mainly focus on the integro-differential equations that are commonly used for modelling quantum-biological systems. Interested readers can learn more about open quantum systems in various books and review articles in both physics and chemistry literature, including the references (Kraus, 1983; Breuer and Petruccione, 2002; Kubo et al., 2003; Weiss, 2008; May and Kühn, 2011).
7 - Environment-assisted quantum transport
- from Part II - Quantum effects in bacterial photosynthetic energy transfer
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- By Masoud Mohseni, Google, Alñn Aspuru-Guzik, Harvard University, Patrick Rebentrost, Harvard University, Alireza Shabani, University of California, Seth Lloyd, Massachusetts Institute of Technology, Susana F. Huelga, Universität Ulm, Martin B. Plenio, Universität Ulm
- Edited by Masoud Mohseni, Yasser Omar, Gregory S. Engel, University of Chicago, Martin B. Plenio, Universität Ulm, Germany
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- Book:
- Quantum Effects in Biology
- Published online:
- 05 August 2014
- Print publication:
- 07 August 2014, pp 159-176
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- Chapter
- Export citation
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Summary
Transport phenomena at the nanoscale exhibit both quantum (coherent) and classical (noisy) behaviour. Coherent and incoherent transfer are normally viewed as limiting cases of a certain underlying dynamics. However, there exist parameter regimes where an intricate interplay between environmental noise and quantum coherence emerges, and whose net effect is an increase in the efficiency of the transport process. In this chapter we illustrate this phenomenon in the context of excitation transport across quantum networks. These are model systems for the description of energy transfer within molecular complexes and, in particular, photosynthetic pigment–protein molecules, a type of biologically relevant structures whose dynamics has been recently shown to exhibit quantum coherent features. We show that nearly perfect transport efficiency is achieved in a regime that utilizes both coherent and noisy features, and argue that Nature may have chosen this intermediate regime to operate optimally.
Introduction
The dynamical behaviour of a quantum system can be substantially affected by interaction with a fluctuating environment and one might initially be led to expect a negative effect on quantum transport involving coherent hopping of a (quasi-) particle between localized sites. In this section, however, we demonstrate that quantum transport efficiency can be enhanced by a dynamical interplay of the quantum dynamics imposed by the system Hamiltonian with the pure dephasing induced by a fluctuating environment.