Macroscopic Dipole Coherence Phenomena

Partha Ghose

Erwin Louis Hahn

Principles of coherent radiation are reviewed as they apply to the coherent interaction between two quantum Ievel atomic oscillators and classical radiation fields.The equivalence between electric dipole and magnetic dipole interactions is outlined for macroscopic systems.The power mechanism for formation of coherent signals is briefly calculated.The self-induced transparency mechanism and area-theorem connected with this mechanism serves as a means of predicting properties of photon echoes.It is stressed that when the classical field is a self-consistent solution to both the equations of the density matrix and Maxwell's equations a reaction field need not be added.

Elisabetta Sassaroli, Yogendra Narain Srivastava, J. Swain +1 more

Axel Stenquist

In the present thesis, the interaction between atoms in superposition states and attosecond pulses is studied from the microscopic to the macroscopic regime. Using a semi-classical framework, three different models have been explored in order to investigate attosecond light--matter interaction processes. The first model is a microscopic, single-atom model. Through using this model, the absorption and the radiation of an external attosecond pulse was studied for several atomic superposition states and pulse energies. The second model was composed by two coupled atoms, where the interaction was described by either dipole-dipole or radiation interaction. The model was validated by simulating the Förster resonant phenomena. In addition, this model was used to determine the behaviour of the interactions with respect to separation distance and the initial states of the atoms. It was found that dipole-dipole interaction is dominant in the near field, whilst radiation interaction is dominant in the far field. Additionally, it was found that superpositions with high principal quantum numbers increase the strength of the dipole-dipole interaction but not the radiation interaction. The simulated results have been validated, in the short-time regime, using perturbation theory. The last model investigated in this thesis is a macroscopic many-atom model. It was implemented in order to simulate the propagation of an attosecond pulse through a large sample of atoms. Utilising this model, collective effects of many-atom systems were studied. It was found that a macroscopic sample emits collimated radiation and that dissipation of pulse energy in a macroscopic sample retains the behaviour of radiation produced by a single atom but that it is deformed by the propagation through the sample. The models explored in this thesis can be used in the study of light-matter interaction on the attosecond timescale with inter-atomic interactions and collective effects. The work presented here can be built on further to investigate research areas such as the dipole-blockade effect in cold atom physics, ionisation due to inter-atomic interaction or collective coherent effects.

Ulrich Weiß, Hermann Grabert

Ai‐Xia Zhang, Ju-Kui Xue

We propose a scheme to reveal the interplay between dipole–dipole interaction (DDI), inter-level coupling and macroscopic phase transitions in dipolar condensates. By considering a macroscopic sample of dipolar bosons in triple-well potentials, DDI-induced coupling between the inter-level physics and the macroscopic phase transitions is presented. When the DDI exceeds certain thresholds, the degeneracy of the two lowest energy levels and the excitation of new eigenstates occur, respectively. Interestingly, these thresholds give the boundaries of various quantum phase transitions. That is, the quantum phase transitions are the consequence of the levels' degeneracy and the new eigenstates' excitation. Furthermore, DDI-induced long-range macroscopic Josephson oscillations are observed and long-range coherent quantum transportation is achieved. Our results give clear proof of the interplay between the multi-level physics and quantum phase transitions, and also provide a way for designing the long-range coherent quantum transportation.