6,606 research outputs found

    Comment on "Neutron Interferometric Observation of Noncyclic Phase"

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    A critique of a recent experiment [Wagh et.al., Phys.Rev.Lett.81, 1992 (7 Sep 1998)] to measure the noncyclic phase associated with a precessing neutron spin in a neutron interferometer, as given by the Pancharatnam criterion, is presented. It is pointed out that since the experiment measures, not the noncyclic phase itself, but a quantity derived from it, it misses the most interesting feature of such a phase, namely the different sign associated with states lying in the upper and the lower hemispheres, a feature originating in the existence of a phase singularity. Such effects have earlier been predicted and seen in optical interference experiments using polarization of light as the spinor [Bhandari, Phys.Rep.281, 1 (Mar 1997)].Comment: 5 pages, 0 figures, submitted to Phys.Rev.Let

    On Geometric Phase from Pure Projections

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    The geometric phase is usually treated as a quantity modulo 2\pi, a convention carried over from early work on the subject. The results of a series of optical interference experiments involving polarization of light, done by the present author (reviewed in R.Bhandari, Phys. Rep. 281 (1997) p.1) question the usefulness of such a definition of the geometric phase in that it throws away useful and measurable information about the system, for example strengths of singularities giving rise to the geometric phase. Such singularities have been directly demonstrated by phase-shift measurement in interference experiments. In this paper, two recent polarization experiments (Hariharan et.al., J.Mod.Opt. 44 (1997)p.707 and Berry and Klein, J.Mod.Opt. 43 (1996)p.165) are analysed and compared with previous experiments and potentially detectible singularities in these experiments pointed out.Comment: Latex, 15 pages, 6 figures; ([email protected]

    Observable Dirac-type singularities in Berry's phase and the monopole

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    The physical reality and observability of 2n\pi Berry phases, as opposed to the usually considered modulo 2\pi topological phases is demonstrated with the help of computer simulation of a model adiabatic evolution whose parameters are varied along a closed loop in the parameter space. Using the analogy of Berry's phase with the Dirac monopole, it is concluded that an interferometer loop taken around a magnetic monopole of strength n/2 yields an observable 2n\pi phase shift, where n is an integer. An experiment to observe the effect is proposed.Comment: 12 pages Latex, 3 postscript figures; submitted to Physical Review Letters 15 September 2000; revised 19 November 200

    On singularities of the mixed state phase

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    A recent proposal of Sjoqvist et.al. to extend Pancharatnam's criterion for phase difference between two different pure states to the case of mixed states in quantum mechanics is analyzed and the existence of phase singularities in the parameter space of an interference experiment with particles in mixed states pointed out. In the vicinity of such singular points the phase changes sharply and precisely at these points it becomes undefined. A closed circuit in the parameter space around such points results in a measurable phase shift equal to 2n\pi, where n is an integer. Such effects have earlier been observed in interference experiments with pure polarization states of light, a system isomorphic to the spin-1/2 system in quantum mechanics. Implications of phase singularities for the interpretation of experiments with partially polarized and unpolarized neutrons are discussed. New kinds of topological phases involving variables representing decoherence (depolarization) of pure states are predicted and experiments to verify them suggested.Comment: 4 pages Latex, 1 postscript figure; submitted to Physical Review Letters 12 Dec 2000; Revised on 13 August 200

    Exploring the Potentialities of Special Economic Zones in Nepal

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    Special Economic Zones (SEZs) have been established in many countries around the world as a way to promote economic growth and attract foreign investment. In Nepal, the potential of SEZs has been recognized as a way to boost the economy, but there is a lack of comprehensive research on the potentialities and challenges of establishing SEZs in the country. This study aims to explore the potentialities of SEZs in Nepal by examining the concept of SEZs, the current state of SEZs in Nepal, and the experiences of other countries with SEZs. The study will be conducted using a combination of literature review, data analysis, stakeholder interviews, case studies, and scenario planning. The study will use a combination of literature review, data analysis, stakeholder interviews, case studies, and scenario planning to explore the potentialities of SEZs in Nepal. The findings of the study will provide valuable insights for policymakers and stakeholders in Nepal to support the growth and development of SEZs in the country. The study will also contribute to the larger body of knowledge on SEZs and their role in economic development. In conclusion, the study will provide a comprehensive analysis of the potentialities of SEZs in Nepal and offer recommendations for effective implementation and development. The study will contribute to the understanding of SEZs as a tool for promoting economic growth and attracting foreign investment in Nepal.How to cite this article: Bhandari, R., (2023). Exploring the Potentialities of Special Economic Zones in Nepal. GS Spark: Journal of Applied Academic Discourse. 1(1), 35-44. https://doi.org/10.5281/zenodo.837205

    Lattice polarization effects on the screened Coulomb interaction WW of the GW approximation

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    In polar insulators where longitudinal and transverse optical phonon modes differ substantially, the electron-phonon coupling affects the energy-band structure primarily through the long-range Fr\"ohlich contribution to the Fan term. This diagram has the same structure as the GWGW self-energy where WW originates from the electron part of the screened coulomb interaction. The two can be conveniently combined by combining electron and lattice contributions to the polarizability. Both contributions are nonanalytic at the origin, and diverge as 1/q21/q^2 so that the predominant contribution comes from a small region around q=0q{=}0. Here we adopt a simple estimate for the Fr\"ohlich contribution by assuming that the entire phonon part can be attributed to a small volume of qq near q=0q{=}0. We estimate the magnitude for q0\mathbf{q}{\rightarrow}0 from a generalized Lyddane-Sachs-Teller relation, and the radius from the inverse of the polaron length scale. The gap correction is shown to agree with Fr\"ohlich's simple estimate αPωL/2-\alpha_P\omega_L/2 of the polaron effect

    Relation between geometric phases of entangled bi-partite systems and their subsystems

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    This paper focuses on the geometric phase of entangled states of bi-partite systems under bi-local unitary evolution. We investigate the relation between the geometric phase of the system and those of the subsystems. It is shown that (1) the geometric phase of cyclic entangled states with non-degenerate eigenvalues can always be decomposed into a sum of weighted non-modular pure state phases pertaining to the separable components of the Schmidt decomposition, though the same cannot be said in the non-cyclic case, and (2) the geometric phase of the mixed state of one subsystem is generally different from that of the entangled state even by keeping the other subsystem fixed, but the two phases are the same when the evolution operator satisfies conditions where each component in the Schmidt decomposition is parallel transported
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