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Roberto Laura

Publications and source records attributed to Roberto Laura.

12 recordsLinked to original sources
arXiv2019

Frauchiger-Renner argument and quantum histories

In this article we reconstruct the Frauchiger and Renner argument, taking into account that the assertions of the argument are made at different times. To do this, we use a formalism of quantum histories, namely the Theory of Consistent Histories. We show that the supposedly contradictory conclusion of the argument requires computing probabilities in a family of histories that does not satisfy the consistency condition, i.e., an invalid family of histories for the theory.

quant-ph↗
arXiv2014

Interpretations of Quantum Theory in the Light of Modern Cosmology

The difficult issues related to the interpretation of quantum mechanics and, in particular, the "measurement problem" are revisited using as motivation the process of generation of structure from quantum fluctuations in inflationary cosmology. The unessential mathematical complexity of the particular problem is bypassed, facilitating the discussion of the conceptual issues, by considering, within the paradigm set up by the cosmological problem, another problem where symmetry serves as a focal point: a simplified version of Mott's problem.

gr-qc↗
arXiv2014

Quantum histories without contrary inferences

In the consistent histories formulation of quantum theory it was shown that it is possible to retrodict contrary properties. We show that this problem do not appear in our formalism of generalized contexts for quantum histories.

quant-ph↗
arXiv2009

A general theoretical framework for decoherence in open and closed systems

A general theoretical framework for decoherence is proposed, which encompasses formalisms originally devised to deal just with open or with closed systems. The conditions for decoherence are clearly stated and the relaxation and decoherence times are compared. Finally, the spin-bath model is developed in detail from the new perspective.

quant-ph↗
arXiv2006

Decoherence in closed and open systems

A generalized formal framework for decoherence, that can be used both in open and closed quantum systems, is sketched. In this context, the relationship between the decoherence of a closed system and the decoherence of its subsystems is studied, and the corresponding decoherence times are defined: for macroscopic systems, the decoherence time of the closed system is much greater than the decoherence time of its subsystems. Finally, it is shown that the application of the new formal framework to a well-known model leads to physically adequate results.

quant-ph↗
arXiv2000

Functional Approach to Quantum Decoherence and the Classical Final Limit

For a wide set of quantum systems it is demonstrated that the quantum regime can be considered as the transient phase while the final classical statistical regime is a permanent state. A basis where exact matrix decoherence appears for these final states is found. The relation with the decoherence of histories formalism is studied. A set of final intrinsically consistent histories is found.

quant-ph↗
arXiv2000

Perturbative method for generalized spectral decompositions

Imposing analytic properties to states and observables we construct a perturbative method to obtain a generalized biorthogonal system of eigenvalues and eigenvectors for quantum unstable systems. A decay process can be described using this generalized spectral decomposition, and the final generalized state is obtained.

quant-ph↗
arXiv1999

Internal Time Superoperator for Quantum Systems with Diagonal Singularity

We generalize the concepts of Internal Time Superoperator, its associated non unitary similarity transformations and Liapounov variables, to quantum systems with diagonal singularity, and we give a constructive proof of the existence of these superoperators for systems with purely diagonal Hamiltonian having uniform absolutely continuous spectrum on the interval from zero to infinity.

quant-ph↗
arXiv1999

Subdynamics theory in the functional approach to quantum mechanics

The formalism of subdynamics is extended to the functional approach of quantum systems, and used for the Friedrichs model, in which diagonal singularities in states and observables are included. We compute in this approach the generalized eigenvectors and eigenvalues of the Liouvulle-Von Newmann operator, using an iterative scheme. As complex generalized eigenvalues are obtained, the decay rates of unstable modes are included in the spectral decomposition.

quant-ph↗
arXiv1996

Minimal Irreversible Quantum Mechanics

It is demonstrated that, making minimal changes in ordinary quantum mechanics, a reasonable irreversible quantum mechanics can be obtained. This theory has a more general spectral decompositions, with eigenvectors corresponding to unstable states that vanish when $t \to \infty .$ These ''Gamov vectors'' have zero norm, in such a way that the norm and the energy of the physical states remain constant. The evolution operator has no inverse, showing that we are really dealing with a time-asymmetric theory. Using Friedrichs model reasonable physical results are obtained, e. g. : the remaining of an unstable decaying state reappears, in the continuous spectrum of the model, with its primitive energy.

quant-ph↗