Creating and sharing knowledge for telecommunications

Seminar - A bit a of quantum in bacterial photosynthetic complexes


on 07-11-2014

... Niek van Hulst, ICFO – The Institute of Photonic Sciences

07/11/2014, 14:00
Room P9, Mathematics Building, IST


I will address the role of quantum effects in photosynthesis. Exploring individual pigment-protein complexes (LH2) of a purple bacterium with coherent fs pulses it is observed that ultrafast quantum coherent energy transfer occurs under physiological conditions. Surprisingly quantum coherences between electronically coupled energy eigen-states persist at least 400 fs, and distinct, time-varying energy transfer pathways can be identified in each complex. Interestingly the single molecule approach allows to track coherent phase jumps between different pathways, which suggest that long-lived quantum coherence renders energy transfer robust in the presence of disorder.

The photosynthetic antenna complexes are efficient in energy transfer, yet such complexes are not designed to emit light and thus hard to observe at the level of individual units. We have developed nanofabrication methods to couple single pigment complexes resonantly to a gold nanoantenna. This way the fluorescence decay speeds up from nanosecond to picosecond timescale, the quantum efficiency is enhanced and up to 1000 times more emission is collected. Using the bright photon emission, we revealed that the bacterial LH2 complex with 27 bacteriochlorophylls coordinated in two rings of chromophores shows photon anti-bunching at ambient conditions, i.e. a bacterial complex acting as a non-classical single-photon emitter.

Quantum Computation and Information Seminar
http://math.tecnico.ulisboa.pt/seminars/qci/?action=next

Support: Phys-Info (IT), SQIG (IT), CFIF and CAMGSD, with support from FCT, FEDER and EU FP7, namely via the Doctoral Programme in the Physics and Mathematics of Information (DP-PMI), and projects PEst-OE/EEI/LA0008/2013, CQVibes, Landauer (318287) and PAPETS (323901). More Information..

Talk - Verification of Markov chains and its relation to the Skolem Problem


on 31-10-2014

... The talk of Manuel Biscaia had to be postponed to this Friday, October 31. To Manuel and to the participants my apologies for the inconvenience.
Verification of Markov chains and its relation to the Skolem Problem

Manuel Biscaia, SQIG - Instituto de Telecomunicações

October 31, 2014, Friday, 16h15m.

Abstract: When studying probabilistic dynamical systems, temporal logic has typically been used to reason about path properties. Recently, there has been some interest in reasoning about the dynamical evolution of state probabilities of these systems. In this paper we show that verifying linear temporal properties concerning the state evolution induced by a Markov chain is equivalent to the decidability of the Skolem problem -- a long standing open problem in Number Theory. However, from a practical point of view, usually it is enough to check properties up to some acceptable error bound. We show that an approximate version of Skolem problem is decidable, and that it can be applied to verify, up to an arbitrarily small error, linear temporal properties of the state evolution induced by a Markov chain.
L states that whenever {γ1,…,γk}⊢Lα there is a proof in which each formula occurrence is either a sub-formula of α or of some of γi. In this work we extend Statman's result and show that any propositional (possibly modal) structural logic satisfying a particular statement of the sub-formula principle is PSPACE-complete. As a consequence, EXPTIME-complete propositional logics, such as PDL and the common-knowledge epistemic logic with at least 2 agents satisfy this particular sub-formula principle, if and only if, PSPACE=EXPTIME.

Room: 3.10, Mathematics

Support: SQIG/Instituto de Telecomunicações with support from FCT and FEDER namely by the FCT project PEst-OE/EEI/LA0008/2013. More Information..