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

Transcript of QuantumBiology_AlexandraM_Liguori

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