No description available.

Entanglement is one of the most technologically important quantum phenomena and its con-trolled creation brings us a step closer to the realisation of a quantum computer. Hybrid electron and nuclear spin systems which combine long nuclear decoherence times with the high polarisation and rapid processing times of electron spins are considered reliable candidates for the representation of the fundamental building block of a quantum computer, the qubit. In the literature electron spins quite often play the role of a mediator which can access, manipulate and couple states with long coherence times, beneficial for storing quantum information. Despite the fact that an electron spin can be a useful resource for nuclear spin systems, its permanent presence can be a source of decoherence. The use of transient photoexcited electron spins provide an additional advantage and once the operations which involve the electron spin are completed, the electron spin can decay and not interfere further with the evolution of the system. In this thesis we report magnetic resonance experiments and density functional theory calculations for the demonstration of nuclear - nuclear entanglement using photoexcited triplet states. We study homonuclear and heteronuclear fullerene derivatives and we identify in each case the relevant parameters that can lead to high fidelity entangling operations. The hyperfine interaction in a homonuclear system is the key parameter which determines the degree of entanglement between the nucelar spins according to a recent theoretical proposal. We measure and calculate the hyperfine interaction in homonuclear systems with ¹³C nuclear spins in order to prove the feasibility of this scheme. Further experiments on a fullerene system with two nuclear spins a ³¹P and a ¹H show that entangling operations of high fidelity which involve the demonstration of CNOT gates, are possible within the lifetime of the triplet state.

Mémoire numérisé par la Direction des bibliothèques de l'Université de Montréal.

Efficient singlet-singlet (SSET) and triplet-triplet (TTET) energy transfer between fluorenyl and either phenylbenzoyl or naphthyl chromophores in enantiomerically pure dipeptides occur via through-space intramolecular dipole-induced dipole (Förster-SSET) and electron exchange (Dexter-TTET) mechanisms as demonstrated by, UV-visible absorption, fluorescence, phosphorescence and laser flash photolysis measurements. Unprotected, optically pure 3-(2-fluorenyl)-L-alanine (8, Fla) and its C- and N-protected derivatives were synthesized using a modified Sorensen procedure, and were subsequently used for solution-phase synthesis of the dipeptides (9, Bpa-Fla and 10,Npa-Fla) and solid-phase synthesis of a 15-residue peptide (7). UV absorption spectra of the dipeptides indicate that the chromophores do not interact electronically in the ground state nor do their photophysical characteristics change when incorporated into the peptides. Dipeptide bichromophore fluorescence and phosphorescence results show efficient SSET (kSSET > 109 s-1) and TTET (kTTET > 104 s-1). Fluorescence and phosphorescence spectra produced by excitation at donor absorbance wavelengths show complete energy transfer in 9 and efficient energy transfer in 10. Donor-acceptor separation (transfer separation distance) was calculated from the spectral overlap of the donor fluorescence spectrum and the acceptor UV absorption spectrum using the Förster equation for energy transfer. With the spectral overlap value, assumed orientation of the chromophores in the dipeptide and the fluorescence quantum yield of the donor, a "critical" Förster transfer distance was calculated for the two dipeptides (9, 10) to be 14.6 Ã… and 15.1 Ã…, respectively. The actual distance calculated from dipeptide fluorescence spectra, using an assumed Förster distance was 9.1 Ã… and 8.7 Ã…, respectively. HyperChem MM3 modeling of the two dipeptides yielded an average inter-chromophore separation of 11 ±3 Ã…, comparable to the experimental values. Laser flash photolysis of the two dipeptides revealed near complete TTET. The spectral analysis of each dipeptide showed essentially 100% acceptor triplet present, although the donor in each case absorbed all or most of the incident light.

This dissertation describes our study of a photophysical process that leads to ultrafast generation of triplet excitons following photoexcitation, singlet exciton fission, in three different acene dimers and diradicaloids. In pentacene and tetracene dimers, we investigate their mechanism of singlet fission. In a series of diradicaloids, we study the relation between molecular structure, diradical character and the suitability for singlet fission. In the first two chapters we explore singlet fission in pentacene dimer. We demonstrate fast and highly efficient intramolecular singlet fission, consisting of two covalently attached pentacene units. The singlet fission pathway is governed by the energy gap between singlet and charge-transfer states, which change dynamically with molecular geometry but are primarily set by the side group. The process exhibits a sensitivity to solvent polarity and competes with geometric relaxation in the singlet state, while subsequent triplet decay is strongly dependent on conformational freedom. The near orthogonal arrangement of the pentacene units is unlike any structure currently proposed for efficient singlet fission and points toward new molecular design rules. Furthermore, these results are the first to demonstrate the role of charge-transfer states in singlet fission and highlight the importance of solubilising groups to optimise excited-state photophysics. In the next chapter, we examine singlet fission in tetracene dimer, where singlet fission is energetically unfavourable. We demonstrate triplet yield as high as 190% can be achieved via fission from higher singlet excited states mediated by charge-transfer states. The outcomes of this study provide deeper insight into the role of hot singlet states in singlet fission and point toward less stringent molecular design rules. In the last chapter, we shift our focus on a new class of molecules, diradicaloid molecules. We explore a family of zethrene molecules, with tuneable diradical character, and demonstrate their general ability to undergo rapid singlet fission via spin-entangled and emissive triplet-pair state TT. A wide range of zethrene molecules are found to be suitable for singlet fission, with additional benefits of high absorption coefficients and photo-/chemical stability.

In this thesis I explore the possibilities of detecting doubly charged Higgs bosons from the Higgs Triplet Model (HTM) at the Large Hadron Collider (LHC) at CERN. Higgs bosons are included into the Standard Model (SM) of particle physics in order to explain the origin of mass of the elementary particles. Even though the SM is considered to be a reliable starting point for any particle theory, no Higgs particles have to this day been found. There are therefore high expectations for the record-breaking energies of the LHC to lead to a Higgs discovery. The HTM produces seven different Higgs bosons, and among these we find the doubly charged ones. Because of their exotic charge, I focus on studying these Higgs particles in particular. To this purpose, I implement the full HTM theory as an alternative model option in standard particle physics Monte-Carlo software and then simulate LHC proton-proton collisions at a center of mass energy of 14 TeV. The investigated signal is defined as two like-signed leptons, four hard jets and missing energy in the final state. The main production mechanisms are pair-production and associated production with a singly charged Higgs. Since I choose to study a region of parameter space where the triplet vacuum expectation value is relatively large, the doubly charged Higgs decays into W's and the singly charged Higgs into WZ or tb. The results of the simulations show that the LHC could probe Higgs masses up to at least 300 GeV with an integrated luminosity of about 300 fb.1.

Reproduction de : Thèse de doctorat : Lasers, molécules, rayonnement atmosphérique : Lille 1 : 2006. / N° d'ordre (Lille 1) : 3920. Titre provenant de la page de titre du document numérisé. Bibliogr. p. 183-188.

Not available / text

The aim of this study was to develop a Digit Triplet Test (DTT) using NZ English. The DTT is a hearing screening tool that uses spoken numbers presented in background noise to estimate speech recognition thresholds (SRTn). The NZ DTT will be made available via telephone or the internet, and will provide each person who completes the screening test with information about whether they should seek a professional hearing assessment. Normal-hearing participants (22 listeners) with hearing thresholds ≤20 dB HL were tested to establish the intelligibility of the individual digits at various signal-to-noise ratios (-20; -17.5; -15.0; -12.5; -10.0; -7.5; and -5.0 dB). The mid-points of the resulting psychometric functions were then used to adjust the level of each digit to achieve the same intelligibility. A SRT of -10.40 ± 1.75 dB SNR for the broadband presentation was established for the separate ear triplet test with the average slope of 17.3%/dB ± 3.9 %/dB for the ten test lists generated. The binaural ear DTT results were compared to best ear threshold PTA and found to have a highly significant correlation (r = 0.816, p<0.001) and a significant correlation to the QuickSIN sentence-in-noise test (r = 0.668, p<0.001). The binaural triplet test was found to have a sensitivity of 100% and specificity of 85%. The separate ear DTT results were compared to the best ear threshold pure tone audiometry and found to have a highly significant correlation (r = 0.809, p<0.001). The separate ear triplet test was found to have a sensitivity of 88% and specificity of 81% (1 – specificity = 0.187). The internet version of the DTT hearing screening test will provide New Zealanders with an easily accessible and objective test that will raise awareness about hearing and hopefully reduce the length of time people take before seeking advice about their hearing.

Thesis (Ph. D.)--University of Texas at Austin, 2002. / Vita. Includes bibliographical references. Available also from UMI Company.