Susana F. Huelga - Unicamiqis2008.df.unicam.it/iqis2008_files/Huelga.pdf · Susana F. Huelga...
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Dephasing Assisted Transport: Quantum Networks and Biomolecules Susana F. Huelga University of Hertfordshire Work supported by IQIS2008, Camerino (Italy), October 26th 2008 Collaboration: Imperial College London
Transcript of Susana F. Huelga - Unicamiqis2008.df.unicam.it/iqis2008_files/Huelga.pdf · Susana F. Huelga...
Dephasing Assisted Transport:Quantum Networks and Biomolecules
Susana F. HuelgaUniversity of Hertfordshire
Work supported by
IQIS2008, Camerino (Italy), October 26th 2008
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Collaboration:Imperial College London
Outline
• Noisy Entanglement [a selected review]
• Noise-assisted transport of excitations
• Linear Chains• The role of entanglement• Experimental Realizations• Complex Networks --- Biomolecules• Beyond Born-Markov framework
• Conclusions/Future work
Isn’t it the case that noise can only mean trouble???
From theZ-list (1998)
Useful tool (2008)
Isn’t it the case that noise can only mean trouble???
Innsbruck-IFCO, October 2008arXiv:0810.1847
Beam splitter destroys which-pathinformation! A detected photon could havecome from any cavity. Entanglement may ariseS. Bose, Plenio, Knight, Vedral, PRL83, 5158 (1999)Browne, Plenio, SH, PRL 91, 067901(2003)
Beyond noise as a mediator of generalized measurements
Entanglement in open, driven, non-equilibrium systems
Stochastic Resonance-like Effects
Can entanglement be generated out of just incoherent sources?
Plenio & Huelga, Phys. Rev. Lett. 88, 197901 (2002) and Nature Physics Highlights May 2002
Related work: Braun, PRL 89, 277901 (2001); Benatti, Floreanini & Piani PRL 91, 070402 (2003)
Thermal driving
Log-Negativity
Noise Intensity
Specific characterization of a novel SR phenomenon Need to identify suitable measures of SR for composite
systems (dynamical and information theoretic)
Introduce additional controllable parameter: coherentinter-qubit coupling J
Uncorrelatedenvironments
The system: A chain of N weakly driven, ZZ coupled spinsunder the transverse action of independent baths
Building block: N=2Amenable to analytic solution
Huelga & Plenio, PRL 98,170601 (2007)
But can one refer to this phenomenon as SR??
Steady state is PPT (Separable)
Steady state entanglement
LO
CA
LIZ
AT
ION
DE
LO
CA
LIZ
ED
We need delocalization to create entanglement
Is non-monotonic as a function of
Information-theoretic measures of SR
Mutual Information
Beyond Born-Markov: Phenomena persistsUbiquity? Phenomena keepsreappearing in a varietyof scenarios
A chain of driven “spins”subject to a form ofcorrelated environment
Di Franco, Paternostro, Tsomokos & SH, PRA 77, 062337 (2008)
SR-effects in a quantum communication set up
New J. Phys 10 (2008), arXiv:0807.4902
Related, independent resultsSee Aspuru-Guzik group, arXiv0806.4725, arXiv:0807.4725
In a given time T, how much of the initial population insite 1 can be transferred to site N+1 (trapping site)and how is the transport affected by noise?
Which role does entanglement play in the process?
Linear Chains
Homogeneous linear chains with nearest neighbour interactions
N+1
We find that the optimal choice of dephasing rates is zero, for arbitrary choicesof
Tool: Directed random walk algorithm
Analytical expressions can be derived for small N in the steady state
General Proof missing
Non-uniform linear chains:
Noise can significantly enhance the transmission rate of excitations
Interpretation: Line broadening due to local dephasing
Is the percentual improvement in efficiency always small?
Transport of excitations can be assisted by local dephasingWhat about quantum coherence properties during the transport process?
Quantum capacity: Propagate one half of a maximally entangledstate across the chain for optimized local dephasing rates
+Φ
A very simple experimental demonstration
Noise Assisted Transport and Photosynthesis
Reaction Centre
6 CO2
+ 12 H O2
+ energy
6 C H O6 12 6
+ 6 O2+ 6 H O
2
From linear chains to fully connected networks
Motivation: Simplified models for the transfer of excitons in the FMO complex
Noise Assisted Transport and Photosynthesis
Reaction Centre
6 CO2
+ 12 H O2
+ energy
6 C H O6 12 6
+ 6 O2+ 6 H O
2
From linear chains to fully connected networks
Motivation: Simplified models for the transfer of excitons in the FMO complex
Noise Assisted Transport and Photosynthesis
Loss of excitation
Transfer to reaction centre
6 CO2
+ 12 H O2
6 C H O6 12 6
+ 6 CO2+ 6 H O
2
+ energy
Reaction Centre
Exchange of excitation
Complex Networks and light harvesting molecules
Observed exciton transfer time cannot beobtained with a purely coherent evolution
Local dephasing enhances the transfer rate of excitations
(Units 1.2414 10^{-4} eV)
Site 3 couples to the reaction center at site 8=
Measured lifetime of exciton is approx. 1 ns which yields
Local dephasing does lead to a strong enhancement of the excitation transfer in a realistic complex network
Noise Assisted Transport and Photosynthesis
Plenio & Huelga, New J. Phys. 2008
Mohseni, Rebentrost, Lloyd, Aspuru-Guzik, J. Phys. Chem. 2008
Beyond the Born-Markov framework
Noise Assisted Transport and Photosynthesis
No dephasing
Some dephasing
Plenio & Huelga, New J. Phys. 2008
Mohseni, Rebentrost, Lloyd, Aspuru-Guzik, J. Phys. Chem. 2008
Noise Assisted Transport and Photosynthesis
No dephasing
Some dephasing
Plenio & Huelga, New J. Phys. 2008
Mohseni, Rebentrost, Lloyd, Aspuru-Guzik, J. Phys. Chem. 2008
More dephasing
Noise Assisted Transport and Photosynthesis
No dephasing
Some dephasing
Plenio & Huelga, New J. Phys. 2008
Mohseni, Rebentrost, Lloyd, Aspuru-Guzik, J. Phys. Chem. 2008
More dephasing
No photons: Destructive interference !
A very intuitive example
MB Plenio, Clifford Paterson Lecture at the RS London
Photons arrive thanks tonoise !
Related work: Quantum Babinet PrincipleTsomokos, Plenio, de Vega & SH, arXiv:0808.2261
Conclusions
Strategy of just minimizing noise may betoo restrictive for many purposes
Learn how/when fully exploit the interplaycoherent-dissipative dynamics
What is next ?• Noise-assisted processes in general quantum channels(formal approach)• Full analysis under complex environment (non-Markovianbaths, strong coupling, forms of collective decoherence)
Neil Oxtoby, Angel Rivas, DimitrisTsomokos, Shash Virmani and SH+ Alex Chin and Ivette Fuentes-Schuller)
QIP at UH
Beyond Born-Markov: Phenomena persistsUbiquity? Phenomena keepsreappearing in a varietyof scenarios
Procedure:
Take Move to an interaction picture with respect to
Assume that Introduce effective modes
Beam splitter transformations
Solving the dynamics
Hamiltonian part:
Liouvillian:
Solving the dynamics
Entanglement from white noise and loss
Quantify entanglementbetween the two cavitymodes, trace out atom.
Plenio & Huelga, PRL 88, 197901 (2002)
Entanglement from white noise and loss
Quantify entanglementbetween the two cavitymodes, trace out atom.
No cavity decay
No entanglement
Quantify entanglementbetween the two cavitymodes, trace out atom.
No cavity decay
No entanglement
No white noise
No entanglement
Entanglement from white noise and loss
Quantify entanglementbetween the two cavitymodes, trace out atom.
No cavity decay
No entanglement
No white noise
No entanglement
Maximal entanglement at intermediate noise levels
Entanglement from white noise and loss
Separable
Vacuum
Thermal
Non-classical
Vacuum
Noiseless cavity: Steady state solution for effective mode is a thermal distribution
Understanding the dynamics
Separable
Vacuum
Thermal
Non-classical
Vacuum
Noiseless cavity: Steady state solution for effective mode is a thermal distribution
Understanding the dynamics
Plenio & Huelga, PRL 88, 197901 (2002)
Separable
Vacuum
Thermal
Non-classical
Vacuum
For finite κ, things are different
Understanding the dynamics
Plenio & Huelga, PRL 88, 197901 (2002)
+Φ
+Φ
