QuantumBiology_AlexandraM_Liguori
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Explaining photosynthesis with Quantum Mechanics Dr. Alexandra M. Liguori Work done with: Dr. Ines De Vega, Prof. Susana Huelga, and Prof. Martin B. Plenio Institut f ¨ ur Theoretische Physik, Universit¨ at Ulm June 8, 2011 A. Liguori Explaining photosynthesis with Quantum Mechanics
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Explaining photosynthesis with Quantum Mechanics
Dr. Alexandra M. LiguoriWork done with: Dr. Ines De Vega, Prof. Susana Huelga,
and Prof. Martin B. Plenio
Institut fur Theoretische Physik, Universitat Ulm
June 8, 2011
A. Liguori Explaining photosynthesis with Quantum Mechanics
Photosynthetic systems
A. Liguori Explaining photosynthesis with Quantum Mechanics
Not only plants but many bacteria also use photosynthesis. Some examples:
Figure: Green sulphur bacteria Fenna-Matthew-Olson complex
Figure: Purple bacteria Rhodobacter
A. Liguori Explaining photosynthesis with Quantum Mechanics
Rhodobacter...
A. Liguori Explaining photosynthesis with Quantum Mechanics
Rhodobacter...
Each single batterium absorbs 1 photon every 10 hours but has an extremelyhigh efficiency, over 90%, i.e. every 10 photons which get absorbed 9 of them areefficiently used to activate the process of photosynthesis and only 1 photon islost!
A. Liguori Explaining photosynthesis with Quantum Mechanics
System we studied
→
ΓRC
RC ΓLH12
J22nk
J11nk
ΓLH12
Two questions:1 explain the very high efficiency of these systems2 try and explain their structure, e.g. why so many rings (=antennas) instead
of only one...
A. Liguori Explaining photosynthesis with Quantum Mechanics
Our results
ΓRC
RC ΓLH12
J22nk
J11nk
ΓLH12
0 500 1000 1500 20000
0.2
0.4
0.6
0.8
1
tP R
C(t)
nLH2=1nLH2=2nLH2=3nLH2=4nLH2=5nLH2=6nLH2=1,...,6
Efficiency measured by the integrated population in the RC, PRC(t), as a functionof time t :
CLASSICAL CASE: at most PRC(t) = 0.16667 = 16 regardless of the
number of external rings (=antennas)
QUANTUM CASE: PRC(t) > 0.9⇔ efficiency of about 90% and improvingwith increasing number of external rings!
A. Liguori Explaining photosynthesis with Quantum Mechanics
ΓRC
RC ΓLH12
J22nk
J11nk
ΓLH12
on average 1 photon every 10 hours⇒ only 1exciton at the time in the systemCLASSICALLY: solve with rate equations⇒ nocoherences, only populations involved:
1 energy transported by the single exciton proceedsslowly
2 system is rigid, i.e. efficiency does not change withdifferent numbers of external rings (=antennas)
QUANTUMLY: solve with quantum masterequation⇒ thanks to coherences the system canbe in a superposition state:
1 energy transported by the single exciton proceedsfaster
2 having more external rings permits more coherencesand therefore more efficient transport to the RC
Take-home message
The very high efficiency and flexibility of these photosynthetic systems canonly be explained with Quantum Mechanics and not with classical rateequations!
A. Liguori Explaining photosynthesis with Quantum Mechanics
ΓRC
RC ΓLH12
J22nk
J11nk
ΓLH12
on average 1 photon every 10 hours⇒ only 1exciton at the time in the systemCLASSICALLY: solve with rate equations⇒ nocoherences, only populations involved:
1 energy transported by the single exciton proceedsslowly
2 system is rigid, i.e. efficiency does not change withdifferent numbers of external rings (=antennas)
QUANTUMLY: solve with quantum masterequation⇒ thanks to coherences the system canbe in a superposition state:
1 energy transported by the single exciton proceedsfaster
2 having more external rings permits more coherencesand therefore more efficient transport to the RC
Take-home message
The very high efficiency and flexibility of these photosynthetic systems canonly be explained with Quantum Mechanics and not with classical rateequations!
A. Liguori Explaining photosynthesis with Quantum Mechanics
