• Volume 6, Issue 3

      March 1976,   pages  117-187

    • Interaction between classical and quantum systems and the measurement of quantum observables

      E C G Sudarshan

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      Quantum mechanics presumes classical measuring instruments with which they interact. The problem of measurement interaction between classical and quantum systems is posed and solved. The restriction to compatible measurements comes about naturally as the condition for the integrity of the classical system. A technical device is the perspective on classical mechanics as quantum mechanics with essentially hidden dynamical variables.

    • A quantum approach to paramagnetic resonance

      Pranawa Deshmukh Sudha Krishnaswamy

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      In the semi-classical theory of the problem of interaction of radio-frequency (r.f.) field with electron or nuclear spin, the application of quantisation is restricted to the spin system only, the r.f. field being treated classically. In this paper, a purely quantum approach is discussed for a system with spin > 1/2 using a Glauber vector to describe coherent excitations of the r.f. field. It is illustrated here for the case of spin 3/2. One finds that this quantum approach contains the classical one.

    • Entropy, information and Maxwell’s demon after quantum mechanics

      Rajendra Bhandari

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      The problem of the subjective nature of entropy and its relation to information and irreversibility is examined in the light of the quantum measurement problem. The main thesis of the paper is that state collapse during a measurement and hence entropy increase in the observed universe is seen by observers who are only able to observe a restricted manifold of states determined by their concepts, language, etc., in short by their level of perception. The thesis leads to the assertion that any universe with a structure must evolve.

    • Alpha decay of isobaric analogue states in24Mg and28Si

      Amit Roy M L Jhingan K V Iyengar

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      Theα-decay of isobaric analogue states (which are forbidden by isospin selection rules) excited in24Mg and28Si through preton capture by23Na atEp=677 and 739 keV and by27Al atEp=295, 327 and 405 keV, respectively, have been studied using solid state track detectors. The ratio ofα-decay widths of the two resonance states in24Mg to the state at 1.632 MeV (2+) in20Ne yields the value 0.065 for the mixing parameterε and the value 4.01 keV for the Coulomb matrix element responsible for the isospin mixing in24Mg.

      In28Si the measurement of theα-decay widths of the three resonance states resulted in the determination of the proton, gamma and alpha partial widths which comprise the total width of the resonance states. Limits have been set for the value of the two mixing parameters involved in this case. Upper limits of 16 and 39 keV have been obtained for the Coulomb matrix elements responsible for the isospin mixing in28Si.

    • Interface exciton modes and superconducting transition temperature of a metal in contact with a semiconductor

      S Rangarajan Sudhanshu S Jha

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      The problem of superconductivity in a metal-semiconductor system has been studied, using the dielectric formulation of superconductivity. The charge redistribution due to the quantum penetration of the metallic electrons to the semi-conductor side is approximated by a simple exponential function. The interface exciton modes are obtained within the framework of classical electrostatics, and their effect in modifying the effective electron-electron interaction near the interface is investigated. It is found that the strength of the excitonic term is small, and by itself, insufficient to lead to superconductivity. Nevertheless, it can alter the superconducting transition temperature of a metal, if it is already superconducting due to some other mechanism. This has been studied as a function of the various parameters entering in the problem.

    • Reflectance spectra and thermoluminescence of NaF coloured in an electrodeless discharge

      S V Moharil B T Deshmukh

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      A comparative study ofγ-ray colouration and electrodeless discharge excitation is reported for NaF. New absorption bands and glow peaks were found. These are shown to be characteristic of electrodeless discharge method of colouration. These are attributed to the multiple types of defects. Further, it is shown that the process by which such defects are formed is strongly temperature dependant. A tentative explanation for the peculiar characteristic of the electrodeless discharge excitation is put forth. The possibility of exploiting these peculiarities for the study of certain properties of colour centres is pointed out.

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