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- ItemSingle Molecules for Quantum Information and Metrology(2024) Escalante, Richard; Maze Ríos, Jerónimo; Pontificia Universidad Católica de Chile. Facultad de FísicaSingle luminescent molecules provide a unique approach in the development of quantum technologies utilizing single photon sources. This includes quantum metrology by using a molecule’s sensitivity of its emission and magnetic properties to the local environment. In this thesis, we present our investigation of the optical properties of several different classes of luminescent molecules. We begin by providing some theoretical background of single quantum emitters as well as a brief description of the experimental methodologies and equipment. Next, we present an optical investigation of an ensemble of iron phthalocyanines molecules. This molecule possesses a ground state triplet, which is a desirable property for optically active spin qubits, but has a very weak optical emission. Diffraction limited spots displayed photo-instability in the form of blinking and irreversible bleaching. In ensemble form however, their optical stability allowed us to identify a possible Raman peak where we calculated the associated phonon frequency. Next, we present our single molecule study of vanadium phthalocyanine. This molecule has been documented as displaying very long spin coherence times even at room temperatures. We confirmed the presence of a single molecule by measuring the second order correlation function. Additionally, we looked at the intensity and spectral response as a function of the excitation laser polarization. The spectrum was fitted to a two Gaussian function, which may correspond to the two dipole transitions as suggested by theoretical calculations. Lastly, we looked at the optical properties of rare earth europium complexes known for having very sharp optical transitions in the emission spectrum, with each having varying levels of sensitivity to the local environment. Motivated by techniques to investigate non-radiative decay channels, we looked at the optical response of four different europium complexes under two 1 µs pulses of 515 nm laser separated by 1 µs. Each displayed a very different results and allowed us to identify the best candidates for single molecule studies. Finally, we looked at the emission spectrum as well as the optical response under a 6 µs long pulse using time-correlation single photon spectroscopy.
- ItemDelving into the phenomenology of very special relativity: from subatomic particles to binary stars(2024) Santoni, Alessandro; Muñoz Tavera, Enrique; Koch, Benjamin; Pontificia Universidad Católica de Chile. Facultad de FísicaEn esta tesis, se investigan las implicaciones de las teorías de violación de Lorentz (LV), enfocándose en Very Special Relativity (VSR) y sus consecuencias fenomenológicas. Presentada inicialmente como un mecanismo alternativo para las masas de los neutrinos, VSR se ha convertido en una parte significativa del marco general de la LV, distinguida por su estructura de grupo y la presencia de operadores no locales.Después de una introducción exhaustiva a los principios de la LV y VSR, presentamos sus modificaciones a la ecuación de Dirac. Una parte significativa de la tesis está dedicada al desarrollo de un formalismo Hamiltoniano dentro del contexto de VSR, abordando sus no-localidades. Este enfoque se extiende al límite no relativista, conectándolo al esquema de Schrödinger.Luego establecemos límites superiores en los parámetros de VSR, examinando sus correcciones a una amplia gama de sistemas y escenarios físicos, como los niveles de Landau de partículas cargadas, el factor g de los electrones, el espectro de energía de neutrones ultrafríos en el campo gravitatorio terrestre, y la emisión gravitacional de estrellas binarias. Este último análisis nos llevó a la construcción de una teoría de campo en VSR para partículas de espín-2, que resultó acomodar una masa del gravitón gauge-invariante.Mediante este estudio, conectamos varias predicciones teóricas con datos experimentales, allanando el camino para futuras exploraciones en teorías de LV y evidenciando su potencial para abordar preguntas no resueltas en la física moderna.
- ItemQuantum measurement transition and entanglement of trapped ions and optomechanical systems(2024) Araya Sossa, Kevin Jordan; Orszag Posa, Miguel; Pontificia Universidad Católica de Chile. Instituto de FísicaAlthough quantum mechanics has been able to explain a wide range of physical, chemical, and even biological events with unprecedented accuracy, fundamental problems remain. For instance, the problem of quantum measurement and quantum entanglement, which are the most perplexing problems that have persisted since the foundation of quantum mechanics. Both are crucial quantum resources with broad applications in quantum information science, quantum computing and quantum optics. For this reason, this thesis is devoted to research the quantum measurement from the weakest regime to the strongest one as well as the dynamics of entanglement of different quantum systems. In this work, we study the measurement transition for a coherent-squeezed pointer state through a transition factor Γ that involves a system-pointer coupling by using an arbitrary measured observable A. In addition, we show that the shift in the pointer’s position and momentum establishes a relationship with a new value defined as the transition value, which generalizes the weak value as well as the conditional expectation value. Furthermore, a new strategy is introduced to achieve different measurement regimes by just adjusting the r and ϕξ parameters of the coherent-squeezed pointer state, opening an interesting way to test quantum mechanics foundations. Our scheme has been theoretically applied in a trapped ion illuminated by a bichromatic laser beam, with a high potential to be implemented in future experimental setups. Besides, we propose a method to regulate the quantum entanglement in the system mentioned before as well as a dispersive-hybrid system where a qubit is directly coupled to a cavity and a mechanical resonator. Entanglement can be controlled by only tuning the squeezing parameters associated with the vibrational mode. As the squeezing amplitude becomes larger, the maximal entanglement abruptly falls to zero at specific squeezing phases. For the hybrid system, it is also possible to generate entanglement for bipartitions from the qubit-cavity-resonator system after applying this strategy. Entangled qubit-cavity states are created through squeezing, even though there is no direct interaction between them. We also analyze the effect of atomic, optical, and vibrational losses on the quantum entanglement. We finally discuss our schemes to be implemented in future experimental setups and promote further studies to generalize the concept of “monogamy of entanglement” in tripartite systems outside qubit-composite states, in particular, (2 ⊗ 2 ⊗ n)-dimensional systems.
- ItemTransport phenomena in nontrivial topological materials(2023) Bonilla Moreno, Daniel Alejandro; Muñoz Tavera, Enrique; Pontificia Universidad Católica de Chile. Instituto de FísicaIn this Ph.D. thesis, we present our work related to electronic quantum transport in materials with nontrivial topology. The fundamental objectives of our work were as follows: Firstly, to study ballistic transport in a nano junction made of a Type I Weyl semimetal material that contains a cylindrical defect created by the application of mechanical strain. In addition to the torsion effect modeled by a pseudo-gauge field, we added an external magnetic field and the repulsive effect of the deformation produced by the mismatch of the crystal lattice. Using the appropriate Landauer ballistic formalism to describe this type of system, we calculated their transport coefficients. Secondly, to study diffusive transport using the linear response regime, of a uniform and diluted concentration of the aforementioned defects through the bulk of a Weyl semimetal slab. For this purpose, we used the standard particle scattering theory, along with Green's functions techniques and diagrammatic methods. Finally, to study the diffusive transport through a single-layer graphene sheet doped with charged impurities, and influenced by the electromagnetic coupling to a topological insulator or a semiconductor. We pursued to investigate the role played by the magneto-electric effect produced by the topological insulator in transport properties, such as electrical conductivity. Here, we also applied a combination of methods based on scattering, linear response, Green's functions, and diagrammatics. We have obtained analytical expressions for the electrical and thermal conductivities, as well as for the Seebeck coefficient. Our results demonstrate the promising nature of these novel topological materials as thermoelectrics for future applications.
- ItemLoops in Holographic Correlators(2023) Muñoz Sandoval, Iván Ignacio; Bañados, Máximo; Pontificia Universidad Católica de Chile. Instituto de FísicaIn the context of the Anti de-Sitter (AdS)/Conformal Field Theory (CFT) correspondence, we investigate the computation of holographic correlation functions for quantum fields in the bulk. Unlike the semi-classical approach, quantum computations involve Infra-Red (IR) and Ultra-Violet (UV) divergences. However, consistent with the semiclassical approximation, we find that IR infinities correspond to boundary divergences, while UV divergences correspond to the bulk. We present a systematic procedure for solving the perturbative quantum problem in the bulk. To illustrate our approach, we consider a Φ4 scalar field on a fixed AdS background and obtain the boundary correlation function in position and momentum space. In position space, we use two approximations: (i) we assume that the field is composed of the classical solution plus a quantum fluctuation, and we solve the classical part before using the holographic dictionary to obtain the quantum correction to the 2- and 4-point functions, requiring UV and IR renormalizations;(ii) using the quantum effective action, we renormalize the UV divergence from the equation of motions and then use the holographic dictionary to obtain the dual correlation function. Both formulations lead to the same conclusions and demonstrate that the bulk theory is renormalizable up to AdS7. Meanwhile, in momentum space, we use the background field method and renormalize the two-point function up to one loop, finding exact agreement with the position space computation. Finally, we provide a general set-up for obtaining the off-shell graviton bulk propagator, which is crucial for obtaining correlation functions for more realistic models.