Browsing by Author "Thorwart, Michael"

Now showing 1 - 3 of 3
  • No Thumbnail Available
    Publication
    Coherent control of an effective two-level system in a non-Markovian biomolecular environment
    (2009-08) Eckel, Jens; Reina Estupiñán, John Henry; Thorwart, Michael
    We investigate the quantum coherent dynamics of an externally driven effective two-level system (TLS) subjected to a slow Ohmic environment characteristic of biomolecular protein–solvent reservoirs in photosynthetic light-harvesting complexes. By means of the numerically exact quasi-adiabatic propagator path integral (QUAPI) method we are able to include non-Markovian features of the environment and show the dependence of the quantum coherence on the characteristic bath cut-off frequency ωc as well as on the driving frequency ωl and the field amplitude A. Our calculations extend from the weak-coupling regime to the incoherent strong-coupling regime. In the latter case, we find evidence for a resonant behaviour, beyond the expected behaviour, when the reorganization energy Er coincides with the driving frequency. Moreover, we investigate how the coherent destruction of tunnelling within the TLS is influenced by the non-Markovian environment.
  • No Thumbnail Available
    Publication
    Enhanced quantum entanglement in the non-Markovian dynamics of biomolecular excitons
    (2009-08) Thorwart, Michael; Eckel, Jens; Reina Estupiñán, John Henry; Nalbach, Peter; Weiss, Stephan
    We show that quantum coherence of biomolecular excitons is maintained over exceedingly long times due to the constructive role of their non-Markovian protein-solvent environment. Using a numerically exact approach, we demonstrate that a slow quantum bath helps to sustain quantum entanglement of two pairs of Forster coupled excitons, in contrast to a Markovian environment. We consider the crossover from a fast to a slow bath and from weak to strong dissipation and show that a slow bath can generate robust entanglement. This persists to surprisingly high temperatures, even higher than the excitonic gap and is absent for a Markovian bath.
  • No Thumbnail Available
    Publication
    Molecular architectures based on π-conjugated block copolymers for global quantum computation
    (2009) Mujica Martínez, Cesar A.; Arce Clavijo, Julio César; Reina Estupiñán, John Henry; Thorwart, Michael
    We propose a molecular setup for the physical implementation of a barrier global quantum computation scheme based on the electron-doped π-conjugated copolymer architecture of nine blocks PPP-PDA-PPP-PA-(CCH-acene)-PA-PPP-PDA-PPP (where each block is an oligomer). The physical carriers of information are electrons coupled through the Coulomb interaction, and the building block of the computing architecture is composed by three adjacent qubit systems in a quasi-linear arrangement, each of them allowing qubit storage, but with the central qubit exhibiting a third accessible state of electronic energy far away from that of the qubits’ transition energy. The third state is reached from one of the computational states by means of an on-resonance coherent laser field, and acts as a barrier mechanism for the direct control of qubit entanglement. Initial estimations of the spontaneous emission decay rates associated to the energy level structure allow us to compute a damping rate of order 10−7 s, which suggest a not so strong coupling to the environment. Our results offer an alloptical, scalable, proposal for global quantum computing based on semiconducting π-conjugated polymers