Dirac's hole theory versus quantum field theory

Dirac's hole theory and quantum field theory are usually considered equivalent to each other. For models of a certain type, however, the equivalence may not hold as we discuss in this Letter. This problem is closely related to the validity of the Pauli principle in intermediate states of perturbation theory.Comment: No figure

Bohmian description of a decaying quantum system

We present a Bohmian description of a decaying quantum system. A particle is initially confined in a region around the origin which is surrounded by a repulsive potential barrier. The particle leaks out in time tunneling through the barrier. We determine Bohm trajectories with which we can visualize various features of the decaying system.Comment: 14 pages, 5 figure

Quantum search with an ensemble of single-query search processes

Recently we introduced an additive composition formulation of an iterative quantum-search algorithm of the Grover type. In this paper, an ensemble-processing scheme suggested by the additive composition is presented. The ensemble-processing consists of single-query search processes and yields the quantum search with certainty. Furthermore we propose a possible quantum circuit for the ensemble processing.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author

Additive composition formulation of the iterative Grover algorithm

In the Grover-type quantum search process a search operator is iteratively applied, say, k times, on the initial uniform superposition database state. We present an additive decomposition scheme such that the iteration process is expressed, in the computational space, as a linear combination of k operators, each of which consists of a single Grover-search followed by an overall phase-rotation. The value of k and the rotation phase are the same as those determined in the framework of the search with certainty. We discuss how the additive form can be effectively utilized and we propose an alternative gate that realizes the same outcome as the iterative search.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author

Situações não usuais originadas da função delta de Dirac e da sua derivada

There is a situation such that, when a function &#131;(<img src="/img/revistas/rbef/v31n4/a04x.gif" align="absmiddle">) is combined with the Dirac delta function &#948;(<img src="/img/revistas/rbef/v31n4/a04x.gif" align="absmiddle">), the usual formula <img src="/img/revistas/rbef/v31n4/a04form01.gif" align="absmiddle">does not hold. A similar situation may also be encountered with the derivative of the delta function &#948;'(<img src="/img/revistas/rbef/v31n4/a04x.gif" align="absmiddle">), regarding the validity of <img src="/img/revistas/rbef/v31n4/a04form02.gif" align="absmiddle">. We present an overview of such unusual situations and elucidate their underlying mechanisms. We discuss implications of the situations regarding the transmission-reflection problem of one-dimensional quantum mechanics.Existe uma situação tal que quando uma função &#131;(<img src="/img/revistas/rbef/v31n4/a04x.gif" align="absmiddle">) é combinada com a função delta de Dirac, &#948;(<img src="/img/revistas/rbef/v31n4/a04x.gif" align="absmiddle">), a formula usual <img src="/img/revistas/rbef/v31n4/a04form01.gif" align="absmiddle"> deixa de ser válida. Uma situação similar pode ocorrer com a derivada da função delta, &#948;'(<img src="/img/revistas/rbef/v31n4/a04x.gif" align="absmiddle">), com relação à formula <img src="/img/revistas/rbef/v31n4/a04form02.gif" align="absmiddle">. Nós apresentamos um apanhado destas situaçãoes não usuais e elucidamos os mecanismos por detrás delas. Nós discutimos as implicações destas situaçãoes em relação ao problema de tranmissão-reflexão em mecânica quântica uni-dimensional