Condensación fotónica en magnetic cavity QED

Román Roche, Juan
Zueco Láinez, David (dir.)

Universidad de Zaragoza, CIEN, 2020
Departamento de Física de la Materia Condensada, Área de Física de la Materia Condensada

Máster Universitario en Física y Tecnologías Físicas

Resumen: More than 47 years ago Hepp and Lieb showed that photon condensation was theoretically possible in Dicke’s model. In this model, symmetry breaking was induced by the coupling of an electromagnetic cavity to the electric dipoles of N free atoms in the thermodynamic limit. The experimental realization of this model has been pursued for the last 47 years. However, the transition has never been measured. During this time, the community has enjoyed a tortuous succession of proposals on how to achieve photon condensation, each shortly matched with a corresponding no-go theorem.
In this Master’s Thesis we present a no-go theorem that unifies all these no-go theorems (including some recent ones) and we propose a rather straightforward way to avoid them: harnessing magnetic coupling. Therefore, we solve this long-standing theoretical controversy and provide a realistic experimental layout to measure the transition, using magnetic molecules (instead of electric-dipole-coupled ones).
This Master’s Thesis is divided in two blocks. The first block discusses the problem of photon condensation as presented in the literature, with electric-dipole coupling. Section 1 starts with a brief presentation of Pauli’s equation and how it leads to the Hamiltonian of the model under study, we then proceed to give a thorough overview of the historical contributions to the topic, from Hepp and Lieb’s original contribution to the present day. Then, in Sec. 2, we present a unified no-go theorem that settles the debate, proving that photon condensation does not occur when the coupling between light and matter is through the electric dipole. The second block explores magnetic cavity QED. In Sec. 3 we introduce Zeeman coupling in our Hamiltonian of the model while considering molecules without electric dipole, we show that this leads to the Dicke model, in which superradiance occurs. After finding that magnetic cavity QED permits photon condensation we test the robustness of the model against some generalizations. Following the success in Sec. 3, in Sec. 4 we discuss a transmission experiment designed to measure the phase transition. Finally, we draw some conclusions from our results and outline possible continuations. Technical details are left for the appendices.

Tipo de Trabajo Académico: Trabajo Fin de Master

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