Vacuum-mediated incoherent processes in coherently prepared media

In the past few decades, dramatic success has been achieved in <br>preparing, modifying, or controlling the matter-light interaction. <br>One approach for this is to use external influences such as electromagnetic <br>fields. Many of these effects share common physical mechanisms, some of <br>which may be summarized as coherence or interference phenomena. Somewhat <br>related to the success of coherent interactions, considerable attention <br>has also been devoted to the study of incoherent processes, such as the <br>spontaneous emission of light by an atom mediated by the surrounding vacuum <br>field. One of the reasons for this interest is that the decoherence due to <br>incoherent processes is one of the major limitations to many schemes of <br>current theoretical and experimental interest. The work in this subject <br>area can be summarized as an effort to inhibit or circumvent the disturbing <br>incoherent processes, which traditionally have been considered inevitable. <br>Incoherent processes, however, are not undesirable a priori. There are also <br>schemes which require the presence of incoherent processes. These different <br>sides of the incoherent processes are also reflected in the current work. <br> <br>The first part I deals with spontaneous emission with the aim of controlling <br>or suppressing the irreversible incoherent evolution due to the emission. <br>In chapter I.1, quantum interference effects are used to suppress <br>the spontaneous emission from the upper to the lower state in an atomic <br>two-level system. These interference effects are induced by an <br>intense external low-frequency field, which creates additional <br>multiphoton pathways. The interference of all possible pathways <br>then accounts for the modified decay dynamics. <br>In chapter I.2, the ansatz is to modify the system dynamics by <br>using incoherent pump fields to induce interference effects. <br>This requires less stringent conditions for the atomic system than <br>spontaneous-emission interference. <br>In the third chapter I.3, we combine the collective effects <br>occurring in a sample of nearby atoms with coherence and <br>interference phenomena usually studied in single-atom systems. <br>This allows for schemes with a rapid system evolution and <br>almost complete population transfer between various system states, <br>depending on sensitive and convenient control parameters. <br>As possible implementation, we discuss <br>the absorption and fluorescence emission properties of the atomic sample <br>which may be used to construct e.g. fast optical switching devices. <br> <br>In part II, we discuss mechanical effects of the matter-light interaction <br>with the emphasis on ground state laser cooling of trapped ions. Here, on the <br>one hand, the momentum transfer caused by the spontaneous decay is crucial <br>in order to cool the trapped particle, but on the other hand, the system needs <br>to be prepared suitably in order to avoid the usual cooling limit due to the <br>recoil of uncontrolled spontaneous emission events. In particular, <br>chapter II.4 discusses a scheme based on double electromagnetically induced <br>transparency (EIT) in order to allow for a complete suppression of the <br>cooling laser field absorption at certain frequencies. This schemes features <br>a fast and almost complete cooling to the mechanical ground-state of the ion. <br>Finally, we discuss the extension to multiple-EIT which allows to cool at <br>different trap frequencies simultaneously. <br>This is of interest e.g. for setups with different axial and radial <br>trap frequencies or for the cooling of ion strings. <br> <br>In the last part III, we make explicit use of incoherent relaxation, <br>as we discuss the resonance fluorescence spectrum of laser-driven few-level <br>atoms. Even though it may seem paradoxical on first sight, in chapter III.5, <br>we propose the incoherent part of the fluorescence spectrum of strongly driven <br>few-level atoms as an interesting candidate for high-precision spectroscopy. <br>For this, we combine ideas from quantum optics and quantum <br>electrodynamics (QED). This can be seen as a first step to treat dynamical <br>processes within the framework of QED. <br>As an application, the outcome of such experiments would allow for a sensitive <br>test of the validity of the dressed-state basis as the natural description <br>of the combined atom-laser system. <br>Chapter III.6 deals with more fundamental questions related to <br>the interpretation of the complex energy shift acquired by a bound electron <br>due to the virtual interactions with the surrounding vacuum. The leading <br>order of this self-energy has a real part, which contributes to the Lamb shift, <br>and an imaginary part, which is interpreted as the inverse lifetime of the given <br>atomic state. This interpretation, however, becomes problematic if one considers <br>the next-higher order corrections (two-loop order). <br>We evaluate the problematic contributions of the squared decay rates <br>and interpret some of these contributions as off-resonant corrections to the <br>photon scattering cross section.

Author dc:creator

• Evers, Jörg

Contributors dc:contributor

• Keitel, Christoph H.

• Inkohärenter Prozess
• Hochpräzisionsspektroskopie
• Kollektiveffekte
• theoretical physics
• quantum optics
• quantum electrodynamics
• incoherent processes
• interference

Repository record source_url

https://freidok.uni-freiburg.de/data/1549

OAI identifier oai:identifier

oai:freidok.uni-freiburg.de:1549