arXiv subjects

E. R. F. Taillebois

Publications and source records attributed to E. R. F. Taillebois.

6 recordsLinked to original sources

arXiv2021

Effective descriptions of localization in a proper-time parametrized framework

Although the quantization of relativistic systems in a proper-time framework gives new insights concerning the understanding of the so-called localization problem, classical observers cannot be treated as quantum comoving frames and real measurement are typically conceived using an external parameter related to a classical frame. Here, the connection between the proper-time formalism and usual descriptions parametrized by classical observers is obtained by defining a restriction operation that mixes contributions of different values of proper-time. Such a restriction procedure allows us to retrieve the concepts of Newton-Wigner position and Kijowski time of detection in an effective fashion, opening the possibility to interpret the related causalities issues as an apparent phenomena resulting from the time uncertainty that is inherent to every physically acceptable single-particle quantum state.

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arXiv2021

On the measurement predictions concerning the intrinsic relativistic spin operator

Although there are several proposals of relativistic spin in the literature, the recognition of intrinsicality as a key characteristic for the definition of this concept is responsible for selecting a single tensor operator that adequately describes such a quantity. This intrinsic definition does not correspond to Wigner's spin operator, which is the definition that is widely adopted in the relativistic quantum information theory literature. Here, the differences between the predictions obtained considering the intrinsic spin and Wigner's spin are investigated. The measurements involving the intrinsic spin are modeled by means of the interaction with an electromagnetic field in a relativistic Stern-Gerlach setup.

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arXiv2020

On a proper-time approach to localization

The causality issues concerning Hegerfeldt's paradox and the localization of relativistic quantum systems are addressed through a proper-time formalism of single-particle operators. The proposed description does not depend on classical parameters connected to an external observer and results in a single-particle formalism in which localization is described by explicitly covariant four-vector operators associated with POVM measurements parametrized by the system's proper-time. As a consequence, it is shown that physically acceptable states are necessarily associated with the existence of a temporal uncertainty and their proper-time evolution is not subject to the causality violation predicted by Hegerfeldt.

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arXiv2020

Localization POVMs and intrinsic temporal uncertainty

The causality issues concerning the localization of relativistic quantum systems, as evidenced by Hegerfeld's paradox, are addressed through a proper-time formalism of single-particle operators. Starting from the premise that physical variables associated to the proper-time gauge have a prominent role in the specification of position, since they do not depend on classical parameters connected to an external observer, we obtain a single-particle formalism in which localization is described by explicitly covariant four-vector operators associated with POVM measurements parametrized by the system's proper-time. Among the consequences of this result, we emphasize that physically acceptable states are necessarily associated with the existence of a temporal uncertainty and their proper-time evolution is not subject to the causality violation predicted by Hegerfeldt.

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arXiv2020

Relativistic spin operator must be intrinsic

Although there are many proposals of relativistic spin observables, there is no agreement about the adequate definition of this quantity. This problem arises from the fact that, in the present literature, there is no consensus concerning the set of properties that such an operator should satisfy. Here we present how to overcome this problem by imposing a condition that everyone should agree about the nature of the relativistic spin observable: it must be intrinsic. The intrinsicality concept is analyzed in the relativistic classical limit and then it is extended to the quantum regime, the spin problem being treated in the context of the irreducible unitary representations of the Poincaré group. This approach rules out three-vector proposals of relativistic spin observable and leads to a unique satisfactory spin definition that, besides being intrinsic, also possesses interesting physical features such as covariance and consistency of predictions in the non relativistic limit. To support the presented results from an operational perspective, a consistent observer-independent model for the electromagnetic-spin interaction is also presented.

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arXiv2013

A new view on spin reduced density matrix for relativistic particles

We present a new interpretation for reduced density matrices of secondary variables in relativistic systems via an analysis of Wigner's method to construct the irreducible unitary representations of the Poincaré group. We argue that the usual partial trace method used to obtain spin reduced matrices is not fully rigorous, however, employing our interpretation, similar effective reduced density matrices can be constructed. In addition, we show that our proposal is more useful than the usual one since we are not restricted only to the reduced density matrices that could be obtained by the ordinary partial trace method.

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