The present thesis can be divided in three parts: 1) Quantum gate teleportation; 2) Numerical search of universal entanglers; 3) Connections between quantum information and number theory. Regarding the quantum gate teleportation, a separability criterion of normal matrices is used to find the analytical conditions of the preservation of separability under conjugation. That analytical condition allowed to find the general formula of an element of $mathbb{C}^{4}$ Clifford group, as well to understand the role of the basis of measurement in the quantum gate teleportation protocol. Considering the searching for universal entanglers, the same separability criterion of normal matrices was used as fitness function in a computational heuristics, in prder to find good candidates for universal entanglers in $mathbb{C}^{3} otimes mathbb{C}^{4}$ and $mathbb{C}^{4} otimes mathbb{C}^{4}$ Hilbert spaces. At last, in the connection of quantum information with the number theory, it is presented the study of the preparation and entanglement of several multi-qubit quantum states based in integer sequences, and the Riemannian quantum circuit, a quantum circuit whose eigenvalues are related to the zeros of the Riemann zeta function. The existence of such circuit proves that is always possible to construct a physical system related to a finite amount of zeros. / A presente tese està dividida em trÃs partes: 1) TeleportaÃÃo de portas quÃnticas; 2) Busca numÃrica por entrelaÃadores universais; 3) ConexÃes entre a informaÃÃo quÃntica e a teoria dos nÃmeros. No que diz a teleportaÃÃo de portas quÃnticas, um critÃrio de separabilidade para matrizes normais à usada para encontrar as condiÃÃes analÃticas da preservaÃÃo da separabilidade sob conjugaÃÃo. Tais condiÃÃes analÃticas permitiram encontrar a forma geral de um elemento do grupo de Clifford em $mathbb{C}^{4}$, assim como tambÃm entender o papel da base de mediÃÃo no protocolo de teleportaÃÃo de portas quÃnticas. Considerando a busca por entrelaÃadores universais, o mesmo critÃrio de separabilidade de matrizes normais foi utilizado como funÃÃo de aptidÃo em uma heurÃstica computacional aplicada para encontrar bons candidatos a entrelaÃadores universais nos espaÃos de Hilbert de dimensÃes $mathbb{C}^{3} otimes mathbb{C}^{4}$ e $mathbb{C}^{4} otimes mathbb{C}^{4}$. Por fim, sobre as conexÃes da informaÃÃo quÃntica com a teoria dos nÃmeros, à apresentado um estudo da preparaÃÃo e entrelaÃamento de vÃrios estados quÃnticos de mÃltiplos qubits baseados em sequÃncias de nÃmeros inteiros. Apresenta-se ainda o circuito quÃntico Riemanniano, um circuito quÃntico cujos autovalores sÃo relacionados aos zeros da funÃÃo Zeta de Riemann. A existÃncia deste circuito prova que à sempre possÃvel construir um sistema fÃsico relacionado a uma quantidade finita de zeros.

Pour d non puissance d’un nombre premier, le nombre maximal de bases deux à deux décorrélées d’un espace de Hilbert de dimension d n’est pas encore connu. Dans ce mémoire, nous commençons par donner une construction de bases décorrélées en lien avec une famille de représentations irréductibles de l'algèbre de Lie su(2) et faisant appel aux sommes de Gauss.Puis nous étudions de façon systématique la possibilité de construire de telle bases au moyen des opérateurs de Pauli. 1) L’étude de la droite projective sur Zdm montre que, pour obtenir des ensembles maximaux de bases décorrélées à l’aide d'opérateurs de Pauli, il est nécessaire de considérer des produits tensoriels de ces opérateurs. 2) Les sous-modules lagrangiens de Zd2n, dont nous donnons une classification complète, rendent compte des ensembles maximalement commutant d'opérateurs de Pauli. Cette classification permet de savoir lesquels de ces ensembles sont susceptibles de donner des bases décorrélées : ils correspondent aux demi-modules lagrangiens, qui s'interprètent encore comme les points isotropes de la droite projective (P(Mat(n, Zd)²),ω). Nous explicitons alors un isomorphisme entre les bases décorrélées ainsi obtenues et les demi-modules lagrangiens distants, ce qui précise aussi la correspondance entre sommes de Gauss et bases décorrélées. 3) Des corollaires sur le groupe de Clifford et l’espace des phases discret sont alors développés.Enfin, nous présentons quelques outils inspirés de l’étude précédente. Nous traitons ainsi du rapport anharmonique sur la sphère de Bloch, de géométrie projective en dimension supérieure, des opérateurs de Pauli continus et nous comparons l'entropie de von Neumann à une mesure de l'intrication par calcul d'un déterminant. / For d not a power of a prime, the maximal number of mutually unbiased bases (MUBs) in a d-dimensional Hilbert space is still unknown. In this thesis, we begin by an original building of MUBs by means of Gauss sums, in relation with a family of irreducible representations of the Lie algebra su(2).Then, we sytematically study the possibility of building such bases by means of Pauli operators. 1) The study of the projective line on Zdm shows that, in order to obtain maximal sets of MUBs, tensorial products of these operators are in order. 2) Lagrangian submodules of Zd2n, of which we give a complete classification, account for maximally commuting sets of Pauli operators. This classification enables to know which of these sets are likely to yield unbiased bases. They correspond to Lagrangian half-modules that can be interpreted as the isotropic points of the projective line (P(Mat(n, Zd)²),ω). Hence, we establish an isomorphism between the unbiased bases thus obtained and distant Lagrangian half-modules, which precises by the way the correspondance between Gauss sums and MUBs. 3) Corollaries on the Clifford group and the finite phase space are then developed.Finally, we present some tools inspired by the previous study. We deal with the cross-ratio on the Bloch sphere and projective geometry in higher dimension, Pauli operators with continuous exponents and we compare von Neumann entropy with a determinantal measure of entanglement