{"id":{"repo_id":"freiburg-diss","oai_identifier":"oai:freidok.uni-freiburg.de:1549"},"canonical_url":"https://search.dev.ndltd.org/etd/freiburg-diss/oai:freidok.uni-freiburg.de:1549","repository":{"repo_id":"freiburg-diss","name":"University of Freiburg","base_url":"https://freidok.uni-freiburg.de/oai/oai2.php"},"display":{"title":"Vacuum-mediated incoherent processes in coherently prepared media","abstract":"In the past few decades, dramatic success has been achieved in
preparing, modifying, or controlling the matter-light interaction.
One approach for this is to use external influences such as electromagnetic
fields. Many of these effects share common physical mechanisms, some of
which may be summarized as coherence or interference phenomena. Somewhat
related to the success of coherent interactions, considerable attention
has also been devoted to the study of incoherent processes, such as the
spontaneous emission of light by an atom mediated by the surrounding vacuum
field. One of the reasons for this interest is that the decoherence due to
incoherent processes is one of the major limitations to many schemes of
current theoretical and experimental interest. The work in this subject
area can be summarized as an effort to inhibit or circumvent the disturbing
incoherent processes, which traditionally have been considered inevitable.
Incoherent processes, however, are not undesirable a priori. There are also
schemes which require the presence of incoherent processes. These different
sides of the incoherent processes are also reflected in the current work.
The first part I deals with spontaneous emission with the aim of controlling
or suppressing the irreversible incoherent evolution due to the emission.
In chapter I.1, quantum interference effects are used to suppress
the spontaneous emission from the upper to the lower state in an atomic
two-level system. These interference effects are induced by an
intense external low-frequency field, which creates additional
multiphoton pathways. The interference of all possible pathways
then accounts for the modified decay dynamics.
In chapter I.2, the ansatz is to modify the system dynamics by
using incoherent pump fields to induce interference effects.
This requires less stringent conditions for the atomic system than
spontaneous-emission interference.
In the third chapter I.3, we combine the collective effects
occurring in a sample of nearby atoms with coherence and
interference phenomena usually studied in single-atom systems.
This allows for schemes with a rapid system evolution and
almost complete population transfer between various system states,
depending on sensitive and convenient control parameters.
As possible implementation, we discuss
the absorption and fluorescence emission properties of the atomic sample
which may be used to construct e.g. fast optical switching devices.
In part II, we discuss mechanical effects of the matter-light interaction
with the emphasis on ground state laser cooling of trapped ions. Here, on the
one hand, the momentum transfer caused by the spontaneous decay is crucial
in order to cool the trapped particle, but on the other hand, the system needs
to be prepared suitably in order to avoid the usual cooling limit due to the
recoil of uncontrolled spontaneous emission events. In particular,
chapter II.4 discusses a scheme based on double electromagnetically induced
transparency (EIT) in order to allow for a complete suppression of the
cooling laser field absorption at certain frequencies. This schemes features
a fast and almost complete cooling to the mechanical ground-state of the ion.
Finally, we discuss the extension to multiple-EIT which allows to cool at
different trap frequencies simultaneously.
This is of interest e.g. for setups with different axial and radial
trap frequencies or for the cooling of ion strings.
In the last part III, we make explicit use of incoherent relaxation,
as we discuss the resonance fluorescence spectrum of laser-driven few-level
atoms. Even though it may seem paradoxical on first sight, in chapter III.5,
we propose the incoherent part of the fluorescence spectrum of strongly driven
few-level atoms as an interesting candidate for high-precision spectroscopy.
For this, we combine ideas from quantum optics and quantum
electrodynamics (QED). This can be seen as a first step to treat dynamical
processes within the framework of QED.
As an application, the outcome of such experiments would allow for a sensitive
test of the validity of the dressed-state basis as the natural description
of the combined atom-laser system.
Chapter III.6 deals with more fundamental questions related to
the interpretation of the complex energy shift acquired by a bound electron
due to the virtual interactions with the surrounding vacuum. The leading
order of this self-energy has a real part, which contributes to the Lamb shift,
and an imaginary part, which is interpreted as the inverse lifetime of the given
atomic state. This interpretation, however, becomes problematic if one considers
the next-higher order corrections (two-loop order).
We evaluate the problematic contributions of the squared decay rates
and interpret some of these contributions as off-resonant corrections to the
photon scattering cross section.","abstract_html":"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.","abstract_has_math":false,"creators":["Evers, Jörg"],"institution":null,"degree_name":null,"degree_level":null,"degree_discipline":null,"degree_department":null,"school":null,"contributors":["Keitel, Christoph H."],"advisors":[],"committee_chairs":[],"committee_members":[],"year":null,"date_issued":"","date_published":null,"updated_at":"2026-07-24T02:22:22Z","subjects":["Inkohärenter Prozess","Hochpräzisionsspektroskopie","Kollektiveffekte","theoretical physics","quantum optics","quantum electrodynamics","incoherent processes","interference"],"languages":[],"rights":[],"rights_urls":[],"identifier_entries":[]},"links":{"outbound_url":"https://freidok.uni-freiburg.de/data/1549","outbound_label":"Repository record","outbound_source":"source_url"},"metadata_groups":[{"id":"people","label":"People","entries":[{"key":"dc:contributor","label":"Contributor","values":["Keitel, Christoph H."]},{"key":"dc:creator","label":"Author","values":["Evers, Jörg"]}]},{"id":"academic_context","label":"Academic Context","entries":[{"key":"dc:type","label":"Dc Type","values":["DoctoralThesis"]}]},{"id":"subjects_keywords","label":"Subjects and Keywords","entries":[{"key":"dc:subject","label":"Dc Subject","values":["Inkohärenter Prozess","Hochpräzisionsspektroskopie","Kollektiveffekte","theoretical physics","quantum optics","quantum electrodynamics","incoherent processes","interference"]}]},{"id":"additional","label":"Additional Metadata","entries":[{"key":"dc:description.abstract","label":"Abstract","values":["In the past few decades, dramatic success has been achieved in
preparing, modifying, or controlling the matter-light interaction.
One approach for this is to use external influences such as electromagnetic
fields. Many of these effects share common physical mechanisms, some of
which may be summarized as coherence or interference phenomena. Somewhat
related to the success of coherent interactions, considerable attention
has also been devoted to the study of incoherent processes, such as the
spontaneous emission of light by an atom mediated by the surrounding vacuum
field. One of the reasons for this interest is that the decoherence due to
incoherent processes is one of the major limitations to many schemes of
current theoretical and experimental interest. The work in this subject
area can be summarized as an effort to inhibit or circumvent the disturbing
incoherent processes, which traditionally have been considered inevitable.
Incoherent processes, however, are not undesirable a priori. There are also
schemes which require the presence of incoherent processes. These different
sides of the incoherent processes are also reflected in the current work.
The first part I deals with spontaneous emission with the aim of controlling
or suppressing the irreversible incoherent evolution due to the emission.
In chapter I.1, quantum interference effects are used to suppress
the spontaneous emission from the upper to the lower state in an atomic
two-level system. These interference effects are induced by an
intense external low-frequency field, which creates additional
multiphoton pathways. The interference of all possible pathways
then accounts for the modified decay dynamics.
In chapter I.2, the ansatz is to modify the system dynamics by
using incoherent pump fields to induce interference effects.
This requires less stringent conditions for the atomic system than
spontaneous-emission interference.
In the third chapter I.3, we combine the collective effects
occurring in a sample of nearby atoms with coherence and
interference phenomena usually studied in single-atom systems.
This allows for schemes with a rapid system evolution and
almost complete population transfer between various system states,
depending on sensitive and convenient control parameters.
As possible implementation, we discuss
the absorption and fluorescence emission properties of the atomic sample
which may be used to construct e.g. fast optical switching devices.
In part II, we discuss mechanical effects of the matter-light interaction
with the emphasis on ground state laser cooling of trapped ions. Here, on the
one hand, the momentum transfer caused by the spontaneous decay is crucial
in order to cool the trapped particle, but on the other hand, the system needs
to be prepared suitably in order to avoid the usual cooling limit due to the
recoil of uncontrolled spontaneous emission events. In particular,
chapter II.4 discusses a scheme based on double electromagnetically induced
transparency (EIT) in order to allow for a complete suppression of the
cooling laser field absorption at certain frequencies. This schemes features
a fast and almost complete cooling to the mechanical ground-state of the ion.
Finally, we discuss the extension to multiple-EIT which allows to cool at
different trap frequencies simultaneously.
This is of interest e.g. for setups with different axial and radial
trap frequencies or for the cooling of ion strings.
In the last part III, we make explicit use of incoherent relaxation,
as we discuss the resonance fluorescence spectrum of laser-driven few-level
atoms. Even though it may seem paradoxical on first sight, in chapter III.5,
we propose the incoherent part of the fluorescence spectrum of strongly driven
few-level atoms as an interesting candidate for high-precision spectroscopy.
For this, we combine ideas from quantum optics and quantum
electrodynamics (QED). This can be seen as a first step to treat dynamical
processes within the framework of QED.
As an application, the outcome of such experiments would allow for a sensitive
test of the validity of the dressed-state basis as the natural description
of the combined atom-laser system.
Chapter III.6 deals with more fundamental questions related to
the interpretation of the complex energy shift acquired by a bound electron
due to the virtual interactions with the surrounding vacuum. The leading
order of this self-energy has a real part, which contributes to the Lamb shift,
and an imaginary part, which is interpreted as the inverse lifetime of the given
atomic state. This interpretation, however, becomes problematic if one considers
the next-higher order corrections (two-loop order).
We evaluate the problematic contributions of the squared decay rates
and interpret some of these contributions as off-resonant corrections to the
photon scattering cross section.","In den letzten Jahren wurden sehr weitreichende Erfolge
bei der Präparation, Modifikation, oder der Kontrolle der
Materie-Licht-Wechselwirkung erzielt. Ein Ansatz ist hierbei
die Verwendung von externen Einflüssen wie etwa elektromagnetische
Felder. Viele der Effekte können dabei als Kohärenz- oder
Interferenzeffekte interpretiert werden.
Analog dazu werden auch inkohärente Prozesse untersucht,
wie etwa die spontane Emission von Licht durch Atome
durch die Wechselwirkung des Atoms mit dem umgebenden Vakuum-Feld.
Eine Hauptmotivation ist dabei, daß solche inkohärenten Prozesse
eine der wesentlichen Einschränkungen sind bei vielen aktuellen
Konfigurationen von theoretischem und experimentellem Interesse.
Das Ziel ist hier also die Unterdrückung oder Umgehung der
störenden inkohärenten Prozesse, die üblicherweise als
unausweichlich betrachtet werden.
Inkohärente Prozesse sind jedoch nicht immer unerwünscht. Es
gibt auch Konfigurationen, die die Anwesenheit von inkohärenten
Prozessen benötigen. Diese verschiedenen Seiten der inkohärenten
Prozesse spiegeln sich auch in dieser Arbeit wieder.
Im ersten Teil I soll die spontane Emission unterdrückt werden,
um die Zeitentwicklung des Systems durch die inkohärenten
Prozesse zu kontrollieren. In Kapitel I.1 wird Quanteninterferenz
ausgenutzt, um den spontanen Zerfall vom oberen zum unteren Zustand in
einem Zweiniveausystem zu kontrollieren.
Diese Interferenzeffekte werden dabei durch ein intensives externes
Niederfrequenzfeld induziert, welches zusätzlich zur normalen
Dynamik Mehrphotonenpfade ermöglicht. Die Interferenz aller möglichen
Pfade erzeugt dann die modifizierte Systemdynamik.
In Kapitel I.2 wird die Systemdynamik durch inkohärente Pumpfelder
erzeugt, die ebenfalls Interferenzeffekte ermöglichen. Der Vorteil
ist hierbei, daß das
verwendete Atom weniger Bedingungen erfüllen muß, um als System
geeignet zu sein.
Im dritten Kapitel I.3 werden Kollektiveffekte, die in einem
Ensemble von dicht benachbarten Atomen auftreten, mit Kohärenz-
und Interferenzphänomenen kombiniert, wie sie üblicherweise
in Einzelatomsystemen untersucht werden.
Diese Kombination erlaubt Systeme mit einer schnellen Zeitentwicklung,
die durch empfindliche Kontrollparameter gesteuert werden können.
Als eine Anwendung werden die optischen Eigenschaften
des atomaren Ensembles diskutiert, die etwa zur Konstruktion
schneller optischer Schaltelemente verwendet werden können.
Im zweiten Teil II geht es um mechanische Effekte in der Materie-Licht-
Wechselwirkung, mit Grundzustandskühlung von gefangenen Ionen
durch Laserfelder als Schwerpunkt. Einerseits wird hier
der Impulstransfer durch die spontane Emission benötigt, um
das gefangene Teilchen kühlen zu können; andererseits
muß die Emission aber kontrolliert werden, damit ein niedriges
Kühllimit erreicht werden kann. Konkret wird in Kapitel II.4
ein Kühlschema diskutiert, das auf doppelter elektromagnetisch
induzierter Transparenz (EIT) basiert. Dieses Schema erlaubt eine schnelle
und fast vollständige Kühlung in den mechanischen Grundzustand des
Ions. Abschließend werden Erweiterung zu vielfacher EIT diskutiert,
mit deren Hilfe man Ionen bei verschiedenen Fallenfrequenzen gleichzeitig
kühlen kann. Dies ist etwa für Aufbauten mit verschiedener Axial- und
Radialfrequenz von Interesse, oder für das Kühlen von Ionenketten.
Der letzte Teil III macht explizit Gebrauch von der inkohärenten
Relaxation.
Auch wenn es zunächst paradox erscheinen mag, wird das inkohärente
Fluoreszenzspektrum von lasergetriebenen atomaren Wenigniveausystemen
als interesanter Kandidat für die
Hochpräzisionsspektroskopie vorgeschlagen. Hierfür werden Ideen
aus der Quantenoptik und der Quantenelektrodynamik (QED) kombiniert.
Dies kann als erster Schritt zur Behandlung dynamischer Prozesse
im Rahmen der QED aufgefaßt werden.
Als Anwendung kann das Ergebnis solcher Experimente verwendet werden,
um die Gültigkeit der verkleideten Zustände als natürliche
Basis des kombinierten Laser-Atom-Systems zu verifizieren.
Kapitel III.6 schließlich befaßt sich mit fundamentalen Fragen
zur Interpretation der komplexen Energieverschiebung,
die ein gebundenes Elektron durch die virtuelle Wechselwirkung
mit dem umgebenden Strahlungsfeld erfährt. Der führende Beitrag
zu dieser Selbstenergie hat einen Realteil, der zur Lamb-Verschiebung
beiträgt, und einen Imaginärteil, der als inverse Lebensdauer des
atomaren Zustands interpretiert wird. Diese Interpretation wird
jedoch problematisch, wenn die nächsthöheren Ordnungen der
Korrekturen berücksichtigt werden (Zweischleifenkorrekturen).
Zunächst wird die Größenordnung des Effektes abgeschätzt durch
die Berechnung der Beiträge der quadratischen Zerfallsraten.
Dann werden einige der Beiträge als nicht-resonante Korrekturen
zum Photonenstreuquerschnitt interpretiert."]},{"key":"dc:format.medium","label":"Dc Format Medium","values":["application/pdf"]},{"key":"dc:title","label":"Title","values":["Vacuum-mediated incoherent processes in coherently prepared media","Durch das Vakuum vermittelte inkohärente Prozesse in kohärent präparierten Medien"]}]}],"canonical_facts":{"dc:contributor":["Keitel, Christoph H."],"dc:creator":["Evers, Jörg"],"dc:description.abstract":["In the past few decades, dramatic success has been achieved in
preparing, modifying, or controlling the matter-light interaction.
One approach for this is to use external influences such as electromagnetic
fields. Many of these effects share common physical mechanisms, some of
which may be summarized as coherence or interference phenomena. Somewhat
related to the success of coherent interactions, considerable attention
has also been devoted to the study of incoherent processes, such as the
spontaneous emission of light by an atom mediated by the surrounding vacuum
field. One of the reasons for this interest is that the decoherence due to
incoherent processes is one of the major limitations to many schemes of
current theoretical and experimental interest. The work in this subject
area can be summarized as an effort to inhibit or circumvent the disturbing
incoherent processes, which traditionally have been considered inevitable.
Incoherent processes, however, are not undesirable a priori. There are also
schemes which require the presence of incoherent processes. These different
sides of the incoherent processes are also reflected in the current work.
The first part I deals with spontaneous emission with the aim of controlling
or suppressing the irreversible incoherent evolution due to the emission.
In chapter I.1, quantum interference effects are used to suppress
the spontaneous emission from the upper to the lower state in an atomic
two-level system. These interference effects are induced by an
intense external low-frequency field, which creates additional
multiphoton pathways. The interference of all possible pathways
then accounts for the modified decay dynamics.
In chapter I.2, the ansatz is to modify the system dynamics by
using incoherent pump fields to induce interference effects.
This requires less stringent conditions for the atomic system than
spontaneous-emission interference.
In the third chapter I.3, we combine the collective effects
occurring in a sample of nearby atoms with coherence and
interference phenomena usually studied in single-atom systems.
This allows for schemes with a rapid system evolution and
almost complete population transfer between various system states,
depending on sensitive and convenient control parameters.
As possible implementation, we discuss
the absorption and fluorescence emission properties of the atomic sample
which may be used to construct e.g. fast optical switching devices.
In part II, we discuss mechanical effects of the matter-light interaction
with the emphasis on ground state laser cooling of trapped ions. Here, on the
one hand, the momentum transfer caused by the spontaneous decay is crucial
in order to cool the trapped particle, but on the other hand, the system needs
to be prepared suitably in order to avoid the usual cooling limit due to the
recoil of uncontrolled spontaneous emission events. In particular,
chapter II.4 discusses a scheme based on double electromagnetically induced
transparency (EIT) in order to allow for a complete suppression of the
cooling laser field absorption at certain frequencies. This schemes features
a fast and almost complete cooling to the mechanical ground-state of the ion.
Finally, we discuss the extension to multiple-EIT which allows to cool at
different trap frequencies simultaneously.
This is of interest e.g. for setups with different axial and radial
trap frequencies or for the cooling of ion strings.
In the last part III, we make explicit use of incoherent relaxation,
as we discuss the resonance fluorescence spectrum of laser-driven few-level
atoms. Even though it may seem paradoxical on first sight, in chapter III.5,
we propose the incoherent part of the fluorescence spectrum of strongly driven
few-level atoms as an interesting candidate for high-precision spectroscopy.
For this, we combine ideas from quantum optics and quantum
electrodynamics (QED). This can be seen as a first step to treat dynamical
processes within the framework of QED.
As an application, the outcome of such experiments would allow for a sensitive
test of the validity of the dressed-state basis as the natural description
of the combined atom-laser system.
Chapter III.6 deals with more fundamental questions related to
the interpretation of the complex energy shift acquired by a bound electron
due to the virtual interactions with the surrounding vacuum. The leading
order of this self-energy has a real part, which contributes to the Lamb shift,
and an imaginary part, which is interpreted as the inverse lifetime of the given
atomic state. This interpretation, however, becomes problematic if one considers
the next-higher order corrections (two-loop order).
We evaluate the problematic contributions of the squared decay rates
and interpret some of these contributions as off-resonant corrections to the
photon scattering cross section.","In den letzten Jahren wurden sehr weitreichende Erfolge
bei der Präparation, Modifikation, oder der Kontrolle der
Materie-Licht-Wechselwirkung erzielt. Ein Ansatz ist hierbei
die Verwendung von externen Einflüssen wie etwa elektromagnetische
Felder. Viele der Effekte können dabei als Kohärenz- oder
Interferenzeffekte interpretiert werden.
Analog dazu werden auch inkohärente Prozesse untersucht,
wie etwa die spontane Emission von Licht durch Atome
durch die Wechselwirkung des Atoms mit dem umgebenden Vakuum-Feld.
Eine Hauptmotivation ist dabei, daß solche inkohärenten Prozesse
eine der wesentlichen Einschränkungen sind bei vielen aktuellen
Konfigurationen von theoretischem und experimentellem Interesse.
Das Ziel ist hier also die Unterdrückung oder Umgehung der
störenden inkohärenten Prozesse, die üblicherweise als
unausweichlich betrachtet werden.
Inkohärente Prozesse sind jedoch nicht immer unerwünscht. Es
gibt auch Konfigurationen, die die Anwesenheit von inkohärenten
Prozessen benötigen. Diese verschiedenen Seiten der inkohärenten
Prozesse spiegeln sich auch in dieser Arbeit wieder.
Im ersten Teil I soll die spontane Emission unterdrückt werden,
um die Zeitentwicklung des Systems durch die inkohärenten
Prozesse zu kontrollieren. In Kapitel I.1 wird Quanteninterferenz
ausgenutzt, um den spontanen Zerfall vom oberen zum unteren Zustand in
einem Zweiniveausystem zu kontrollieren.
Diese Interferenzeffekte werden dabei durch ein intensives externes
Niederfrequenzfeld induziert, welches zusätzlich zur normalen
Dynamik Mehrphotonenpfade ermöglicht. Die Interferenz aller möglichen
Pfade erzeugt dann die modifizierte Systemdynamik.
In Kapitel I.2 wird die Systemdynamik durch inkohärente Pumpfelder
erzeugt, die ebenfalls Interferenzeffekte ermöglichen. Der Vorteil
ist hierbei, daß das
verwendete Atom weniger Bedingungen erfüllen muß, um als System
geeignet zu sein.
Im dritten Kapitel I.3 werden Kollektiveffekte, die in einem
Ensemble von dicht benachbarten Atomen auftreten, mit Kohärenz-
und Interferenzphänomenen kombiniert, wie sie üblicherweise
in Einzelatomsystemen untersucht werden.
Diese Kombination erlaubt Systeme mit einer schnellen Zeitentwicklung,
die durch empfindliche Kontrollparameter gesteuert werden können.
Als eine Anwendung werden die optischen Eigenschaften
des atomaren Ensembles diskutiert, die etwa zur Konstruktion
schneller optischer Schaltelemente verwendet werden können.
Im zweiten Teil II geht es um mechanische Effekte in der Materie-Licht-
Wechselwirkung, mit Grundzustandskühlung von gefangenen Ionen
durch Laserfelder als Schwerpunkt. Einerseits wird hier
der Impulstransfer durch die spontane Emission benötigt, um
das gefangene Teilchen kühlen zu können; andererseits
muß die Emission aber kontrolliert werden, damit ein niedriges
Kühllimit erreicht werden kann. Konkret wird in Kapitel II.4
ein Kühlschema diskutiert, das auf doppelter elektromagnetisch
induzierter Transparenz (EIT) basiert. Dieses Schema erlaubt eine schnelle
und fast vollständige Kühlung in den mechanischen Grundzustand des
Ions. Abschließend werden Erweiterung zu vielfacher EIT diskutiert,
mit deren Hilfe man Ionen bei verschiedenen Fallenfrequenzen gleichzeitig
kühlen kann. Dies ist etwa für Aufbauten mit verschiedener Axial- und
Radialfrequenz von Interesse, oder für das Kühlen von Ionenketten.
Der letzte Teil III macht explizit Gebrauch von der inkohärenten
Relaxation.
Auch wenn es zunächst paradox erscheinen mag, wird das inkohärente
Fluoreszenzspektrum von lasergetriebenen atomaren Wenigniveausystemen
als interesanter Kandidat für die
Hochpräzisionsspektroskopie vorgeschlagen. Hierfür werden Ideen
aus der Quantenoptik und der Quantenelektrodynamik (QED) kombiniert.
Dies kann als erster Schritt zur Behandlung dynamischer Prozesse
im Rahmen der QED aufgefaßt werden.
Als Anwendung kann das Ergebnis solcher Experimente verwendet werden,
um die Gültigkeit der verkleideten Zustände als natürliche
Basis des kombinierten Laser-Atom-Systems zu verifizieren.
Kapitel III.6 schließlich befaßt sich mit fundamentalen Fragen
zur Interpretation der komplexen Energieverschiebung,
die ein gebundenes Elektron durch die virtuelle Wechselwirkung
mit dem umgebenden Strahlungsfeld erfährt. Der führende Beitrag
zu dieser Selbstenergie hat einen Realteil, der zur Lamb-Verschiebung
beiträgt, und einen Imaginärteil, der als inverse Lebensdauer des
atomaren Zustands interpretiert wird. Diese Interpretation wird
jedoch problematisch, wenn die nächsthöheren Ordnungen der
Korrekturen berücksichtigt werden (Zweischleifenkorrekturen).
Zunächst wird die Größenordnung des Effektes abgeschätzt durch
die Berechnung der Beiträge der quadratischen Zerfallsraten.
Dann werden einige der Beiträge als nicht-resonante Korrekturen
zum Photonenstreuquerschnitt interpretiert."],"dc:format.medium":["application/pdf"],"dc:subject":["Inkohärenter Prozess","Hochpräzisionsspektroskopie","Kollektiveffekte","theoretical physics","quantum optics","quantum electrodynamics","incoherent processes","interference"],"dc:title":["Vacuum-mediated incoherent processes in coherently prepared media","Durch das Vakuum vermittelte inkohärente Prozesse in kohärent präparierten Medien"],"dc:type":["DoctoralThesis"]},"updated_at":"2026-07-24T02:22:22Z"}