This thesis focuses on pioneering a scalable route to fabricate quantum information devices based upon single InAs/InP quantum dots emitting in the telecommunications wavelength band around 1550 nm. Using metallic gates in combination with nanotemplate, site-selective epitaxy techniques, arrays of single quantum dots are produced and electrostatically tuned with a high degree of control over the electrical and optical properties of each individual quantum dot. Using metallic gates to apply local electric fields, the number of electrons within each quantum dot can be tuned and the nature of the optical recombination process controlled. Four electrostatic gates mounted along the sides of a square-based, pyramidal nanotemplate in combination with a flat metallic gate on the back of the InP substrate allow the application of electric fields in any direction across a single quantum dot. Using lateral fields provided by the metallic gates on the sidewalls of the pyramid and a vertical electric field able to control the charge state of the quantum dot, the exchange splitting of the exciton, trion and biexciton are measured as a function of gate voltage. A quadrupole electric field configuration is predicted to symmetrize the product of electron and hole wavefunctions within the dot, producing two degenerate exciton states from the two possible optical decay pathways of the biexciton. Building upon these capabilities, the anisotropic exchange splitting between the exciton states within the biexciton cascade is shown to be reversibly tuned through zero for the first time. We show direct control over the electron and hole wavefunction symmetry, thus enabling the entanglement of emitted photon pairs in asymmetric quantum dots. Optical spectroscopy of single InAs/InP quantum dots atop pyramidal nanotemplates in magnetic fields up to 28T is used to examine the dispersion of the s, p and d shell states. The g-factor and diamagnetic shift of the exciton and charged exciton states from over thirty single quantum dots are calculated from the spectra. The g-factor shows a generally linear dependence on dot emission energy, in agreement with previous work on this subject. A positive linear correlation between diamagnetic coefficient and g-factor is observed.

Simulating the nonequilibrium behavior of interacting quantum systems is an important way to understand results of experimental quantum simulators, motivate new materials, and refine new quantum algorithms. However, this is a challenging task due to the exponential difficulty of such systems, which motivates dimensional reduction methods, such as semiclassical limits. This work extends semiclassical phase space methods to spin systems with no clear classical limit with the cluster truncated Wigner approximation (cTWA), and improves on Schrieffer-Wolff low energy effective dynamics with variational adiabatic generators. The cTWA was used to compute nonequilibrium dynamics in spin chains, finding behavior such as signatures of many body localization; rapid thermalization and preservation of fluctuations; effective thermodynamic classical behaviors; and signatures of quantum chaos and butterfly velocities, in 1d spin 1/2 chains. Variational Schrieffer-Wolff methods were used to find efficient non-perturbative dressings for the Hubbard model and find effective quasiparticle dynamics and nonthermal states in quantum chaotic spin chains. These methods are potentially effective tools to separate essential quantum behavior from classical behavior, and can be used to diagnose quantum thermalization behavior in interacting quantum systems.

A l’heure des mégadonnées, du traitement et de l’échange d’informations de masse, le développement de nouvelles technologies liées à l’information est un défi important de notre société. Pour répondre à ce besoin grandissant, le monde de l’infiniment petit régi par les lois de la physique quantique offre d’importantes possibilités de développement technologique. Cette thèse s’inscrit dans le contexte de l’émergence des nouvelles technologies quantiques basées sur l’utilisation d’atomes artificiels. Nous nous sommes particulièrement intéressés aux possibilités offertes par les spins nucléaires uniques dans le diamant. Le début de ce mémoire de thèse vise à introduire les propriétés du défaut NV du diamant dont le spin électronique peut être utilisé pour détecter les spins nucléaires présents dans la matrice de diamant. Le caractère anisotrope de l’interaction hyperfine entre le spin électronique du centre NV et les spins nucléaires de 13C sera exploité pour initialiser l’état de ces spins nucléaires en tirant profit d’un anti-croisement de niveau. La structure particulière des niveaux d’énergie de ce système de spins à l’anti-croisement de niveaux nous permettra de revisiter le phénomène de piégeage cohérent de population avec un spin nucléaire unique à température ambiante. Enfin, en vue des applications technologiques de ce système, nous présenterons la mise en place d’une expérience de détection micro-onde du spin électronique associé au défaut NV permettant de s’affranchir de l’illumination optique qui représente la source principale de décohérence de l’état quantique des spins nucléaires. Les résultats obtenus dans cette thèse, relatifs au contrôle des systèmes de spins dans le diamant, s’inscrivent dans la perspective de développement des systèmes quantiques hybrides. Ainsi, l’association des longs temps de cohérence des spins nucléaires aux performances de calcul des bits quantiques supraconducteurs est une voie prometteuse de développement des technologies quantiques de l’information. / At a time where processing and exchanging big sets of data is one of the main challenge of our society, the development of technologies related to information based on the principles of quantum physics offer interesting new perspectives. This thesis is within the context of the emergence of new quantum technologies based on artificial atoms. We are particularly interested in the opportunities offered by single nuclear spins in diamond. The beginning of this thesis introduces the properties of the NV coloured center of diamond. In particular, we explain how the NV defect electronic spin can be used to detect nuclear spins dispersed in the diamond matrix. By making use, the anisotropic nature of the hyperfine interaction between the NV electron spin and 13C nuclear spins, we demonstrate nuclear spin initialization close to the nuclear spin levels anti-crossing. The specific structure of the spin system’s energy levels enables us to revisit the phenomenon of coherent population trapping with a single nuclear spin at room temperature. Finally, in the aim of developing new technologies based on this spin system, we describe the beginning of a project going towards the implementation of the micro-wave detection of a single electronic spin in diamond. This project is aiming to get rid of the optical illumination which is the main source of decoherence of the nuclear spin quantum state in diamond. The results obtained in this thesis about the control of spin systems in diamond, can be combined with the development of hybrid quantum systems. Thus, the combination of the long coherence time of nuclear spins with the computing performances of superconducting qu-bits is a promising development of quantum information technology.

This dissertation reports high-resolution experimental study and numerical analysis of the rubidium dimer 31Πg, "6" ^"1" "Σ" _"g" ^"+" , "3" ^"3" "Π" _"g" , and "4" ^"3" "Σ" _"g" ^"+" excited electronic states. The term energies of over 2 400 observed ro-vibrational levels spanning a large range of rotational and vibrational quantum numbers were measured with the perturbation facilitated optical-optical double resonance technique 24 000 cm-1 – 26 000 cm-1 above the ground state minimum of Rb2. The excited electronic states were probed by exciting Rb2 molecules from the thermally populated ro-vibrational levels of the "X" ^" 1" "Σ" _"g" ^"+" ground electronic state through intermediate levels of the mixed" " "A" ^"1" "Σ" _"u" ^"+" " ~ " "b" ^"3" "Π" _"u" electronic states. Probe laser resonance was detected by measuring the laser induced fluorescence from the excited electronic states to the "a" ^"3" "Σ" _"u" ^"+" triplet ground state. The ro-vibrational term energies from each electronic state were fit to molecular constants using the Dunham expansion. These molecular constants were subsequently used to generate Rydberg-Klein-Rees model potential energy functions. The spin multiplicity of the electronic states as well as the vibrational numbering of the triplet electronic states were determined by resolving the bound-free emission from the excited ro-vibrational levels to the triplet ground state. / Physics

Entanglement is a key resource in many quantum information schemes andin the last years the research on multi-qubit entanglement has drawn lots ofattention. In this thesis the experimental generation and characterization ofmulti-qubit entanglement is presented. The qubits are implemented in the polarizationdegree of freedom of photons and we have prepared genuine entangledstates of two, four and six photons. We emphasize that one type of states thatwe produce are invariant entangled states, remaining unchanged under simultaneousidentical unitary transformations of all their individual constituents.Such states can be applied to e.g. decoherence-free encoding, quantum communicationwithout sharing a common reference frame, quantum telecloning,secret sharing and remote state preparation schemes.In the experimental implementation we use a single source of entangledphoton pairs and extract the first, second and third order parametric downconversion.The multi-order processes are not entirely spontaneous, as we getthe right states utilizing bosonic emission enhancement due to indistinguishability.Despite the achievement of six-photon entangled states, is the setupcompletely free from interferometric overlaps making it robust and contributingto high fidelities of the generated states. The analysis results of our experimentalstates are in very good agreement with theory and also show very highvisibilities in their correlations.

No description available.

No description available.

No description available.

No description available.

Quantum walks are the quantum mechanical analogue of classical random walks. Discrete-time quantum walks have been introduced and studied mostly on the line Z or higher dimensional space Z d but rarely defined on graphs with fractal dimensions because the coin operator depends on the position and the Fourier transform on the fractals is not defined. Inspired by its nature of classical walks, different quantum walks will be defined by choosing different shift and coin operators. When the coin operator is uniform, the results of classical walks will be obtained upon measurement at each step. Moreover, with measurement at each step, our results reveal more information about the classical random walks. In this dissertation, two graphs with fractal dimensions will be considered. The first one is Sierpinski gasket, a degree-4 regular graph with Hausdorff di- mension of df = ln 3/ ln 2. The second is the Cantor graph derived like Cantor set, with Hausdorff dimension of df = ln 2/ ln 3. The definitions and amplitude functions of the quantum walks will be introduced. The main part of this dissertation is to derive a recursive formula to compute the amplitude Green function. The exiting probability will be computed and compared with the classical results. When the generation of graphs goes to infinity, the recursion of the walks will be investigated and the convergence rates will be obtained and compared with the classical counterparts. / Mathematics