Información cuántica con variables continuas

"This thesis identifies the model of simultaneous measurement of the position and momentum observables seminally posed by Arthurs and Kelly as a system described entirely by observables with continuous eigen spectrum; in particular, we treat the model in the regime of Gaussian states by assuming a minimum uncertainty state as the system under measurement. Under this consideration, the mathematical framework used to describe these states in quantum information processing tasks finds applicability. First, we consider the free energies of each quantum system defining the measurement setting in the measurement dynam ics; then, we study how this consideration affects the retrodictive and predictive aspects of accuracy for the simultaneous measurement of the position and momentum observables of the system under examination. We find that the accuracy of the simultaneous measurement is affected by the degree of coupling between the detectors of the measurement apparatus and the system under observation"

Evolución temporal del estado enredado de un haz de partículas de spín arbitrario en el experimento de Stern-Gerlach

“En una región de campo magnético inhomogéneo, luego, en este lugar, la función de onda asociada a este ensamble de átomos sufre una separación en regiones espacialmente distintas, finalmente esta función de onda colapsa a manera de un par de distribuciones de impacto en una pantalla detectora. En este trabajo se realiza un análisis teórico donde a través del método del operador de evolución se obtiene la evolución temporal del estado cuántico que representa un haz de átomos o moléculas con espín arbitrario en la región del campo magnético del experimento de Stern-Gerlach. Dicha evolución describe las situaciones para un haz polarizado y uno no polarizado (situación correspondiente al experimento de Stern-Gerlach original); los grados de libertad internos son representados por una mezcla estadística de estados y una superposición de estados respectivamente; los grados de libertad externos se representan a través de un paquete de ondas Gaussiano. La evolución obtenida muestra un enredamiento cuántico entre los dos grados de libertad del sistema y a partir de las expresiones obtenidas puede derivarse la evolución temporal para cualquier espín específico. El enredamiento cuántico es caracterizado para el caso puro (la situación del haz polarizado) a través de la entropía de Von Neumann.

Quantum Nonlocality and Quantum Correlations in the Stern–Gerlach Experiment

The Stern–Gerlach experiment (SGE) is one of the foundational experiments in quantum physics. It has been used in both the teaching and the development of quantum mechanics. However, for various reasons, some of its quantum features and implications are not fully addressed or comprehended in the current literature. Hence, the main aim of this paper is to demonstrate that the SGE possesses a quantum nonlocal character that has not previously been visualized or presented before. Accordingly, to show the nonlocality into the SGE, we calculate the quantum correlations C ( z , θ ) by redefining the Banaszek–Wódkiewicz correlation in terms of the Wigner operator, that is C ( z , θ ) = ⟨ Ψ | W ^ ( z , p z ) σ ^ ( θ ) | Ψ ⟩ , where W ^ ( z , p z ) is the Wigner operator, σ ^ ( θ ) is the Pauli spin operator in an arbitrary direction θ and | Ψ ⟩ is the quantum state given by an entangled state of the external degree of freedom and the eigenstates of the spin. We show that this correlation function for the SGE violates the Clauser–Horne–Shimony–Holt Bell inequality. Thus, this feature of the SGE might be interesting for both the teaching of quantum mechanics and to investigate the phenomenon of quantum nonlocality