On time derivatives for <X^> and <p^>: formal 1D calculations

We present formal 1D calculations of the time derivatives of the mean values of the position (x) and momentum (p) operators in the coordinate representation. We call these calculations formal because we do not care for the appropriate class of functions on which the involved (self-adjoint) operators...

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Veröffentlicht in:Revista brasileira de ensino de física 2013-06, Vol.35 (2)
1. Verfasser: De Vincenzo, Salvatore
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Sprache:eng ; por
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Zusammenfassung:We present formal 1D calculations of the time derivatives of the mean values of the position (x) and momentum (p) operators in the coordinate representation. We call these calculations formal because we do not care for the appropriate class of functions on which the involved (self-adjoint) operators and some of its products must act. Throughout the paper, we examine and discuss in detail the conditions under which two pairs of relations involving these derivatives (which have been previously published) can be formally equivalent. We show that the boundary terms present in d{x}/dt and d{x}/dt can be written so that they only depend on the values taken there by the probability density, its spatial derivative, the probability current density and the external potential V= V9 (x) V = V(x). We also show that d(p)/dt is equal to -dv /dx=(FQ) plus a boundary term (Fq = aQ/ax)is the quantum force and Q is the Bohm's quantum potential). We verify that (fq) is simply obtained by evaluating a certain quantity on each end of the interval containing the particle and by subtracting the two results. That quantity is precisely proportional to the integrand of the so-called Fisher information in some particular cases. We have noted that fQ has a significant role in situations in which the particle is confined to a region, even if V is zero inside that region. Apresentamos cálculos formais em 1D das derivadas com respeito ao tempo dos valores médios dos operadores da posição (x) e do momento linear (p) na representação de coordenadas. Chamamos esses cálculos formais porque não nos preocupamos com o tipo apropriado de funções sobre as quais devem atuar os operadores (auto-adjuntos) envolvidos e alguns de seus produtos. Ao longo do artigo, examinamos e discutimos em detalhe as condições em que dois pares de relações que envolvem essas derivadas (que foram previamente publicadas) podem ser formalmente equivalentes. Mostramos que os termos de fronteira presentes em d{x}/dt e d{x}/dt podem ser escritos de modo que eles só dependem dos valores a tomados pela densidade de probabilidade, sua derivada espacial, a densidade de corrente de probabilidade e do potencial externo V = V(x).. Também mostramos que d(p)/dté igual a -dv /dx=(FQ)mais um termo de fronteira ((Fq = aQ/ax)é a força quântica e Q é o potencial quântico de Bohm). Verificamos que (fQ)é obtido simplesmente através do cálculo de uma certa quantidade em cada extremidade do intervalo contendo a partcula e subtraindo os dois
ISSN:1806-1117
1806-1117
DOI:10.1590/S1806-11172013000200008