Vacuum-induced Coherence In Y-type Systems

Quantum interference (QI) is one of the quantum natures of atomic and molec-ular systems that has attracted considerable attention in the last two decades. Quantum phenomena such as electromagnetically induced transparency (EIT), elec-tromagnetically induced absorption (EIA), coherent population trapping (CPT) and spontaneous emission cancellation (SEC) are based on quantum interference. Some of the quantum interference are induced by the external fields, while some are inher-ent to the systems. Vacuum-induced coherence (VIC) [also termed as spontaneously generated coherence (SGC)], which originates from the interaction between vacuum and the system, can give rise to peculiar phenomena. Y-type is a common energy configuration in atomic and molecular systems. Quantum interference in Y-type systems has been widely studied. However, there are few works concentrating on VIC in Y-type systems.In this thesis, we studied the effects of VIC on the photon statistics of Y-type systems via generating function method. We also studied the mean forces exerted by a laser plane wave and a laser standing wave on a two-level atom.In Chapter 1, we introduced the background and listed some well-known quan-tum interference phenomena. We also introduced the photon statistics, generating function method and previous works on quantum interference in Y-type systems.In Chapter 2, we presented our theoretical framework. We derived the master equation of a multi-level single atom and the mean forces exerted by laser fields on a two-level atom.In Chapter 3, we studied the VIC in Y-type systems and presented the numer-ical results. We showed that the system can be transparent or present ultra-narrow absorption lines to the probe field in the presence of maximum VIC. The transparen-cy to probe field can be considered as a result of CPT induced by VIC according to the dressed-state theory. We also studied the influence of wave-vector mismatch on photon statistics of a moving Y-type atom.In Chapter 4, we studied the mean forces exerted by a laser plane wave and a laser standing wave on a two-level atom, respectively. Within the limitations of Bloch framework, we derived the mean radiative force on the atom as a function of average emitted photon number <N> and its time derivatives. Since the mean force is difficult to measure while the photon statistical variables (average emitted photon number, emission intensity, etc.) are relatively easy to obtain, our results provide a potential approach to measure the mean force exerted by laser fields on the atom.In Chapter 5, we gave the conclusions and an outlook.