12,175 research outputs found
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
Some remarks on Dirac's hole theory versus quantum field theory
Dirac's hole theory and quantum field theory are generally considered to be
equivalent to each other. However, it has recently been shown that this is not
necessarily the case. In this article we will discuss the reason for this lack
of equivalence and suggest a possible solution.Comment: Correction to title and other minor changes to reflect the version to
be published in the Canadian Journal of Physic
Detection of coherent light in an incoherent background
The change in position of the self-coherence function minimum is used to detect the presence of a coherent source, rather than the change in strength of the self-coherence function at the reference path difference. The system uses both optical and digital signal processing with MATLAB algorithm. An experimental system was built in the visible band, employing a Michelson interferometer, an interference filter centered in the red, and a silicon photodetector. The results were averaged over up to 50 scans, depending on the relative visibility of the white light and laser fringes, to reduce the scan to scan variability. Amplifier gain was introduced to reduce quantization noise
Doped AB_2 Hubbard Chain: Spiral, Nagaoka and RVB States, Phase Separation and Luttinger Liquid Behavior
We present an extensive numerical study of the Hubbard model on the doped
AB chain, both in the weak coupling and the infinite-U limit. Due to the
special unit cell topology, this system displays a rich variety of phases as
function of hole doping () away from half-filling. Near half-filling,
spiral states develop in the weak coupling regime, while Nagaoka itinerant
ferromagnetism is observed in the infinite-U limit. For higher doping the
system phase-separates before reaching a Mott insulating phase of short-range
RVB states at . Moreover, for we observe a crossover,
which anticipates the Luttinger liquid behavior for .Comment: 11 pages, 13 figure
The difference between Dirac's hole theory and quantum field theory
Dirac's hole theory and quantum field theory are generally thought to be
equivalent. In fact field theory can be derived from hole theory through the
process of second quantization. However, it can be shown that problems worked
in both theories yield different results. The reason for the difference between
the two theories will be examined and the effect the this difference has on the
way calculations are done in quantum theory will be examined.Comment: Accepted as a chapter in "Progress in Quantum Physics Research" Nova
Science Publishers. 62 page
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