Departmental Oral Examination (Thesis Title: "Composite System Quantum Mechanics with Internal Entanglement")

Event Date and Time: 
Tue, 2017-06-06 11:00 - 13:00
Henn 318
Local Contact: 
Physics and Astronomy, UBC
Intended Audience: 

Although many quantum mechanics problems of a point particle have been well understood, the realistic physical model is often a composite system consisting of particles bound together, and its quantum mechanics is an important problem with applications in many areas of physics. Unlike a point particle, a composite object possesses the internal structure described by the degrees of freedom, which are often entangled with each other. We call the entanglement among the degrees of freedom present in the composite system as “internal entanglement” to stress that both entangled degrees of freedom equivalently describe the composite system, as opposed to the situation when the system concerned is entangled with an external object. Examples of the internal entanglement include the entanglement between a vibrational and a rotational mode of a molecule, and that between its position and its internal clock-state etc.

In this thesis, we study quantum mechanics of composite objects by focusing on the effects of the internal entanglement. We firstly look at the tunnelling of a diatomic molecule through a half-silvered mirror in the continuum space and observe that the spatial superposition state of the diatomic molecule made by a half-slivered mirror can decohere by emission of radiation due to the fact that its internal degrees of freedom is entangled with radiation fields, and there exists the entanglement between its position and its internal (i.e., relative position) degrees of freedom. Secondly, we study the lattice analog of 
the above problem in molecular crystals, namely we replace the diatomic molecule by a biexicton, and the half-silvered mirror by an impurity. We 
find that discreteness of a lattice makes the wave vector of a biexicton and the relative distance between two excitons of it inseparable and entangled with each other. We investigate how this inseparability affects the creation of the biexciton-impurity bound states and the entanglement dynamics. Finally we propose a possible application of our study of the internal entanglement to the Anderson model of a composite quasiparticle.
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