Yasser Omar

Quantum Effects in Biology

List of contributors Preface Part I. Introduction: 1. Quantum biology: introduction Graham R. Fleming and Gregory D. Scholes 2. Open quantum system approaches to biological systems Alireza Shabani, Masoud Mohseni, Seogjoo Jang, Akihito Ishizaki, Martin Plenio, Patrick Rebentrost, Al...n Aspuru-Guzik, Jianshu Cao, Seth Lloyd and Robert Silbey 3. Generalized Forster resonance energy transfer Seogjoo Jang, Hoda Hossein-Nejad and Gregory D. Scholes 4. Multidimensional electronic spectroscopy Tomas Mancal Part II. Quantum Effects in Bacterial Photosynthetic Energy Transfer: 5. Structure, function, and quantum dynamics of pigment protein complexes Ioan Kosztin and Klaus Schulten 6. Direct observation of quantum coherence Gregory S. Engel 7. Environment-assisted quantum transport Masoud Mohseni, Al...n Aspuru-Guzik, Patrick Rebentrost, Alireza Shabani, Seth Lloyd, Susana F. Huelga and Martin B. Plenio Part III. Quantum Effects in Higher Organisms and Applications: 8. Excitation energy transfer in higher plants Elisabet Romero, Vladimir I. Novoderezhkin and Rienk van Grondelle 9. Electron transfer in proteins Spiros S. Skourtis 10. A chemical compass for bird navigation Ilia A. Solovyov, Thorsten Ritz, Klaus Schulten and Peter J. Hore 11. Quantum biology of retinal Klaus Schulten and Shigehiko Hayashi 12. Quantum vibrational effects on sense of smell A. M. Stoneham, L. Turin, J. C. Brookes and A. P. Horsfield 13. A perspective on possible manifestations of entanglement in biological systems Hans J. Briegel and Sandu Popescu 14. Design and applications of bio-inspired quantum materials Mohan Sarovar, Dorthe M. Eisele and K. Birgitta Whaley 15. Coherent excitons in carbon nanotubes Leonas Valkunas and Darius Abramavicius Glossary References Index.

Entanglement controlled single-electron transmittivity

We show that the electron transmittivity of single electrons propagating along a one-dimensional (1D) wire in the presence of two magnetic impurities is affected by the entanglement between the impurity spins. For suitable values of the electron wave vector, there are two maximally entangled spin states which, respectively, make the wire completely transparent whatever the electron spin state or strongly inhibit electron transmission.

Graphene-enabled low-control quantum gates between static and mobile spins

We show that the features of Klein tunneling make graphene a unique interface for implementing low control quantum gates between static and mobile qubits. A ballistic electron spin is considered as the mobile qubit, while the static qubit is the electronic spin of a quantum dot fixed in a graphene nanoribbon. Scattering is the low control mechanism of the gate, which in other systems is very difficult to exploit because of both backscattering and the momentum dependence of transmission. We find that the unique features of Klein tunneling enable quasideterministic quantum gates between the spin of a ballistic electron and a static spin held in a dot, regardless of the momenta or the shape of the incident electron wave function. The Dirac equation is used to describe the system in the one particle approximation, with the interaction between the static and the mobile spins modeled by a Heisenberg Hamiltonian. Furthermore, we discuss an application of this model to generate entanglement between two well-separated static qubits.

Electron Fabry–Perot interferometer with two entangled magnetic impurities

We consider a one-dimensional (1D) wire along which single conduction electrons can propagate in the presence of two spin-1/2 magnetic impurities. The electron may be scattered by each impurity via a contact-exchange interaction and thus a spin-flip generally occurs at each scattering event. Adopting a quantum waveguide theory approach, we derive the stationary states of the system at all orders in the electron–impurity exchange coupling constant. This allows us to investigate electron transmission for arbitrary initial states of the two impurity spins. We show that for suitable electron wave vectors, the triplet and singlet maximally entangled spin states of the impurities can respectively largely inhibit the electron transport or make the wire completely transparent for any electron spin state. In the latter case, a resonance condition can always be found, representing an anomalous behaviour compared to typical decoherence induced by magnetic impurities. We provide an explanation for these phenomena in terms of the Hamiltonian symmetries. Finally, a scheme to generate maximally entangled spin states of the two impurities via electron scattering is proposed.

Quantum Thermal Machines Fuelled by Vacuum Forces

We propose a quantum thermal machine composed of two nanomechanical resonators (two membranes suspended over a trench in a substrate) placed a few μm from each other. The quantum thermodynamical cycle is powered by the Casimir interaction between the resonators and the working fluid is the polariton resulting from the mixture of the flexural (out-of-plane) vibrations. With the help of piezoelectric cells, we select and sweep the polariton frequency cyclically. We calculate the performance of the proposed quantum thermal machines and show that high efficiencies are achieved thanks to (i) the strong coupling between the resonators and (ii) the large difference between the membrane stiffnesses. Our findings can be of particular importance for applications in nanomechanical technologies where a sensitive control of temperature is needed.

Quantum Computation and Information

After a very brief survey of the key milestones and open problems in quantum computation and information, the research effort at IST-UTL is outlined, namely, the goals, ongoing tasks and results of the QuantLog project. In order to illustrate some key issues in quantum computation, the problem of minimizing the number of qubits in quantum automata is presented in detail at a level appropriate for non-specialists.

Improving Classical Authentication over a Quantum Channel

We propose a quantum protocol to authenticate classical messages that can be used to replace Wegman–Carter’s classical authentication scheme in quantum key distribution (QKD) protocols. We show that the proposed scheme achieves greater conditional entropy of the seed for the intruder given her (quantum) observation than the classical case. The proposed scheme is suitable for situations where the shared symmetric key used in authentication becomes dangerously short (due to noise or eavesdropping), and there is a threat that it might be completely consumed without being replaced. Our protocol is an improvement over a classical scheme by Brassard and takes advantage of quantum channel properties. It is motivated by information-theoretical results. We stress that the proposed authentication protocol can also be used as an independent authentication protocol that is not a part of a QKD. However by adopting it, QKD becomes a fully quantum protocol. We prove that quantum resources can improve both the secrecy of the key generated by the PRG and the secrecy of the tag obtained with a hidden hash function. We conclude that the proposed quantum encoding offers more security than the classical scheme and, by applying a classical result, we show that it can be used under noisy quantum channels.

Effect of static disorder in an electron fabry-perot interferometer with two quantum scattering centers

In a recent paper—F. Ciccarello et al., New J. Phys. 8, 214 (2006)—we have demonstrated that the electron transmission properties of a one-dimensional (1D) wire with two identical embedded spin-1/2 impurities can be significantly affected by entanglement between the spins of the scattering centers. Such an effect is of particular interest in the control of the transmission of quantum information in nanostructures and can be used as a detection scheme of maximally entangled states of two localized spins. In this letter, we relax the constraint that the two magnetic impurities are equal and investigate how the main results presented in the above paper are affected by a static disorder in the exchange coupling constants of the impurities. Good robustness against deviation from impurity symmetry is found for both the entanglement dependent transmission and the maximally entangled states generation scheme.

Promoting the Public Awareness of Mathematics in Developing Countries: A Responsibility and an Opportunity

In this article we present a case for the importance of promoting the public awareness of mathematics in developing countries. We start by discussing the factors that attract the public to mathematics and argue they are universally valid, including in developing countries, with less educated populations. Based on the experience of the NGO SiW—Scientists in the World, which has developed projects in Africa and South-East Asia, we present several concrete examples of activities raising the public awareness of mathematics in those regions, as well as ideas for possible future projects and recommendations on how to implement them.

Quantum Effects in Biology and Their Applications to Light Harvesting and Sensing

Abstract This session introduced the novel area of quantum effects in biological systems: it presented its seminal experimental discoveries and theoretical ideas, namely regarding photosynthetic systems and olfactory recognition, and discussed their potential applications to the development of artificial devices for more efficient light harvesting and finer sensing.