title: Quantum coherence and correlations in photonic qubits and photoactive hybrid organometallic Perovskite systems
Creators: name: Melo Luna, Carlos Andres
Publisher: name: University of Bayreuth
Year: 2019
Subjects: subject: Quantum Information
subject: Qubits
subject: coherence
subject: information correlation
subject: spectroscopy
subject: lifetime measurement
subject: single-photon quantum source
subject: 530
subject: 540

description: The past two decades have witnessed tremendous advances and breakthroughs in quantum information science and technology, due mainly to the use of quantum physical resources such as coherence and entanglement. The formalization of the concept of universal quantum computing by D. Deutsch in 1985 has matured into commercial initiatives that aim to accelerate the physical implementation of a practical quantum computer. So far, such quantum technology has been pushed forward as information processors that are mainly on superconducting quantum bits (qubits) based. Other developments make use of quantum states of photons in conjunctions with other quantum registers based on electrons, atoms, molecules, artificial systems, between others. Although in any case, multiple qubit technologies are still under intense research and developments and the temperature and size of the quantum register are essential issues. However, all possible physical implementation of quantum information processing devices have in common the fundamental properties of quantum systems: interference, coherence, and entanglement. 
In this thesis, we concerned the study of quantum coherence and entanglement in qubits (encoded on the polarisation basis) and quantum materials (operating at room temperature) to analyze the role of quantum correlations and decoherence for information processing purposes. The current research is divided into two main parts, the first one begins with the analysis of the influence of a birefringent medium over the entanglement of a photonic qubit state. We employ a polarisation maintaining fiber (PMF) as a decohering environment to test the theoretical model in which the symmetry of the coupling between the qubit and environment defines the death and revival of the information correlations. This finding establishes a tool to keep the entanglement independent of the fiber length employing the symmetry properties of the physical system. 
Additionally, to demonstrate that the entanglement is not the only crucial factor in information schemes, we employ the prisoner’s dilemma game (in a two parameters strategy space and extended up to three) to evidence that quantum advantages in this protocol are by the quantum superposition instead of the entanglement of the physical system. Here we also pose an experimental setup with photons to verify our findings with photonic qubits. 
The second part of the thesis examines a novel nanomaterial which could serve up a bridge to the interaction of photons and electrons toward a physical representation of photonic qubits conditioned by external registers (as electrons or ions). The first stage in this direction considers the implementation of single photon emitters. However, previous to it is necessary to recognize the photophysical capabilities of the Perovskites as structure selected. As a complement, the novelty of this nanostructure allow us to give answers to some open questions in this characterization direction in the frame of this research. 
The MA-halide (methylammonium-halide) perovskites are structurally composed by small domains which ranging from nano to micrometer sizes presenting strong photoluminescence intermittency (blinking). We attribute this response to the Auger- nonradiative recombination of additional electrons photogenerated in a trap-filling process due to defects or ion movement. We verified this through the application of an absorbing layer (quencher) of charges of PCBM (Phenyl-C61-butyric acid methyl ester) resulting in considerably decreases in blinking. We also provide a novel technique for real-time observation of the ion movement effect over this material. Additionally, this behavior indicates appropriate conditions for the existence of a few emitters which are useful in quantum protocols and become a motivation to analyze and explain this phenomenon. Then, we prepare two chemical compositions of inorganic Perovskites with a high structural order to explore the necessary conditions to produce single emitter with this material. We visualized the samples through electron microscopy, and both systems were spectrally characterized decreasing dilutions up to observe emission intermittency. We verified the nonclassical behavior of the emission employing a Hanbury Brown-Twiss interferometer by measuring the degree of the second-order coherence correlation function. Finally, but not less important, the additional information presents the laboratories implemented during this doctoral research and the prototype of signals counting device to analyze temporal coincidences in correlated photonic events.