3,118 research outputs found
Effects of an External Field and Dissipation on Decoherence
Decoherence is the suppression of the interference of quantum states. It plays important roles in the study of the quantum-classical transition. It is also the major obstacle in the implementation of various schemes of quantum computers. Decoherence can be affected by many factors. The interactions between quantum systems of interest and dissipative environments cause the extensively studied environment-induced-decoherence. Decoherence can also occur as the result of a temperature effect. A recent experiment investigated the engineering of decoherence, which involves applying an external field to the quantum system. In this thesis, we study the effect of an external field on decoherence in the case of a harmonic oscillator coupled to a heat bath by calculating its contribution to the attenuation coefficient, which is a measure of decoherence in coordinate space and involves directly observable probability distributions. It is found that, while non-random external force does not result in decoherence, a random external force can lead to intrinsic decoherence that does not require a dissipative environment. The attenuation coefficient for a free harmonic oscillator in a dissipative environment is also calculated using the solution of the initial value quantum Langevin equation. One of the key results obtained is that ”decoherence without dissipation” does not occur in the case of a free harmonic oscillator, in contrast to the case of a free particle
Nuclear dependence of azimuthal asymmetry in semi-inclusive deep inelastic scattering
Within the framework of a generalized factorization, semi-inclusive deeply
inelastic scattering (SIDIS) cross sections can be expressed as a series of
products of collinear hard parts and transverse-momentum-dependent (TMD) parton
distributions and correlations. The azimuthal asymmetry $ is studied. It is shown that the azimuthal
asymmetry is suppressed by multiple parton scattering and the transverse
momentum dependence of the suppression depends on the relative shape of the
twist-2 and 3 quark distributions in the nucleon. A Gaussian ansatz for TMD
twist-2 and 3 quark distributions in nucleon is used to demonstrate the nuclear
dependence of the azimuthal asymmetry and to estimate the smearing effect due
to fragmentation.Comment: 9 pages in RevTex with 2 figure
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