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Coherence effects in vacuum-induced processes

Martin Kiffner

Published Jan 1, 2007• 0 citations
Publisher

Abstract

Quantum interference and coherence effects in the interaction of atoms with the quantized electromagnetic field are investigated theoretically. A general master equation for the description of atom-field interactions is introduced. The interplay of the concepts of complementarity and interference in the time-energy domain are studied on the basis of the fluorescence light emitted by a single laser-driven atom, where the coherence of spontaneous processes gives rise to quantum interference in the spectrum of resonance fluorescence. The vacuum-induced dipole-dipole interaction in pairs of multi-level atoms is analyzed. It is shown that the interaction between orthogonal transition dipole moments of different atoms does not only influence the system dynamics crucially, but implies that the few-level approximation in general cannot be applied to near-degenerate Zeeman sublevels of the atomic level scheme. Potential applications of dipole-dipole interacting multi-level atoms for the implementation of decoherence-free subspaces and the generation of entanglement between atomic states are examined. The generation of an entangled state of the radiation field with a macroscopic number of photons is discussed on the basis of a single-atom laser.

DOI
10.11588/heidok.00007386

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Quantum interference and coherence effects in the interaction of atoms with the quantized electromagnetic field are investigated theoretically. A general master equation for the description of atom-field interactions is introduced. The interplay of the concepts of complementarity and interference in the time-energy domain are studied on the basis of the fluorescence light emitted by a single laser-driven atom, where the coherence of spontaneous processes gives rise to quantum interference in the spectrum of resonance fluorescence. The vacuum-induced dipole-dipole interaction in pairs of multi-level atoms is analyzed. It is shown that the interaction between orthogonal transition dipole moments of different atoms does not only influence the system dynamics crucially, but implies that the few-level approximation in general cannot be applied to near-degenerate Zeeman sublevels of the atomic level scheme. Potential applications of dipole-dipole interacting multi-level atoms for the implementation of decoherence-free subspaces and the generation of entanglement between atomic states are examined. The generation of an entangled state of the radiation field with a macroscopic number of photons is discussed on the basis of a single-atom laser.
The interplay of the concepts of complementarity and interference in the time-energy domain are studied. In particular, we theoretically investigate the fluorescence light from a J = 1/2 to J= 1/2 transition that is driven by a monochromatic laser field. We find that the spectrum of resonance fluorescence exhibits a signature of vacuum-mediated interference effects, whereas the total intensity is not affected by interference. We demonstrate that this result is a consequence of the principle of complementarity, applied to time and energy. Since the considered level scheme can be found, e.g., in (198)Hg(+) ions, our model system turns out to be an ideal candidate to provide evidence for as yet experimentally unconfirmed vacuum-induced atomic coherences.
We discuss various aspects of the incoherent spontaneous emission in atomic few-level systems arising from the coupling of the atom to the surrounding vacuum. First, we consider systems where the decoherence due to spontaneous emission acts as a limiting factor. Here, we combine collective effects in larger samples of atoms with control mechanisms known from single-atom schemes, or modify the system dynamics by externally inducing multiphoton quantum interference effects. In the second part, we discuss ground-state laser cooling of trapped atoms and ions. Here, the momentum transfer in the spontaneous emission events is required to cool the particles, but needs to be controlled in order to achieve a low cooling limit. In our scheme, we make use of double electromagnetically induced transparency in order to design the absorption spectrum of the trapped particle. In the final part, we show that the incoherent part of the resonance fluorescence spectrum of a two-level system may serve as an interesting candidate for high-precision spectroscopy. For this, we discuss relativistic and radiative corrections to the resonance fluorescence spectra of laser-driven few-level systems.
Abstract This thesis presents an investigation into the quantum characteristics of fluorescence emitted by a two-level atom placed in the electromagnetic vacuum and driven by a classical coherent field. The theoretical analysis employs the Jaynes–Cummings model together with the master-equation formalism commonly used to describe open quantum systems. Within this framework, the work examines key nonclassical fea tures such as photon antibunching, sub-Poissonian statistics, and quantum regression. Particular emphasis is given to resonance fluorescence and the influence of weak and strong driving fields on the coherence properties of the emitted radiation. The master equation is solved in the long-time limit to obtain the evolution of relevant atomic expectation values, which are subsequently used to study population dynamics, mean photon behavior, and spectral features of the fluorescence signal. The study also highlights the role of vacuum fluctuations in spontaneous emission and their impact on the quantum behavior of the atom, ultimately providing insights into the generation of coherent and nonclassical light from driven atomic systems and their relevance to quantum communication and quantum information technologies. Keywords: Fluorescence, Jaynes–Cummings model, Photon statistics, Quantum optics, Two-level atom
Abstract This thesis presents an investigation into the quantum characteristics of fluorescence emitted by a two-level atom placed in the electromagnetic vacuum and driven by a classical coherent field. The theoretical analysis employs the Jaynes–Cummings model together with the master-equation formalism commonly used to describe open quantum systems. Within this framework, the work examines key nonclassical fea tures such as photon antibunching, sub-Poissonian statistics, and quantum regression. Particular emphasis is given to resonance fluorescence and the influence of weak and strong driving fields on the coherence properties of the emitted radiation. The master equation is solved in the long-time limit to obtain the evolution of relevant atomic expectation values, which are subsequently used to study population dynamics, mean photon behavior, and spectral features of the fluorescence signal. The study also highlights the role of vacuum fluctuations in spontaneous emission and their impact on the quantum behavior of the atom, ultimately providing insights into the generation of coherent and nonclassical light from driven atomic systems and their relevance to quantum communication and quantum information technologies. Keywords: Fluorescence, Jaynes–Cummings model, Photon statistics, Quantum optics, Two-level atom
The resonance fluorescence emitted by a system of two dipole-dipole interacting nearby four-level atoms in a $J=1/2\ensuremath{\leftrightarrow}J=1/2$ configuration is studied. This setup is the simplest realistic model system which provides a complete description of the (inter-atomic) dipole-dipole interaction for arbitrary orientation of the inter-atomic distance vector, and at the same time allows for intra-atomic spontaneously generated coherences. Our main interest is the interplay of both these different coupling mechanisms. We discuss different methods to analyze the contribution of the various vacuum-induced coupling constants to the total resonance fluorescence spectrum. These allow us to find a dressed state interpretation of the contribution of the different inter-atomic dipole-dipole couplings to the total spectrum. We further study the role of the spontaneously generated coherences, and identify two different contributions to the single-particle vacuum-induced couplings. We show that they have a noticeable impact on the total resonance fluorescence spectrum down to small inter-atomic distances, even though the dipole-dipole coupling constants then are much larger in magnitude than the the single-particle coupling constants. Interestingly, we find that the inter-atomic couplings can induce an effect of the intra-atomic spontaneously generated coherences on the observed spectra which is not present in single-atom systems.