{"id":{"repo_id":"lmu-germany","oai_identifier":"oai:edoc.ub.uni-muenchen.de:81"},"canonical_url":"https://search.dev.ndltd.org/etd/lmu-germany/oai:edoc.ub.uni-muenchen.de:81","repository":{"repo_id":"lmu-germany","name":"Ludwig Maxmilians Universität München","base_url":"https://edoc.ub.uni-muenchen.de/cgi/oai2"},"display":{"title":"Entanglement and control of quantum states","abstract":"In the first part of this thesis,we examine the preparation of a single- mode radiation field in arbitrary pure quantum states via resonant inter- action with a sequence of two-level atoms.The preparation is achieved by choosing an appropriate (in general entangled)initial state of the atomic sequence,and does neither require a final state measurement of the atoms,nor a control of the atom-field interaction.Furthermore,the method is applicable also when starting from mixed initial field states. We show how to determine the optimal initial atomic state which pre- pares the desired field state with the maximum fidelity,and prove the feasibility of our state preparation method by numerical calculations. In the second part,we demonstrate the noise-induced control of quantum jumps in a fundamental open quantum system.Here,in addition to the subsequent interaction with a flux of two-level atoms,the quantized field is also coupled to a thermal environment.Under certain experimental conditions,the photon field exhibits a bistable behavior,with quantum jumps between two metastable states.In the presence of a small peri- odic signal (i.e.,a modulation of the initial state of the two-level atoms crossing the single-mode resonator),the best synchronization of these quantum jumps with the signal is achieved at an optimal,nonvanishing temperature of the environment.This stochastic resonance e ffect can be observed in di fferent components of the atomic Bloch vector on exit from the cavity. The third part treats a speci fic problem concerning the characterization of entanglement between two quantum mechanical two-level systems. We consider the optimal decomposition of a two-qubit state into an en- tangled and a separable part,with maximal weight of the latter,and derive necessary and su fficient conditions for the optimality of the de- composition.","abstract_html":"In the first part of this thesis,we examine the preparation of a single- mode radiation field in arbitrary pure quantum states via resonant inter- action with a sequence of two-level atoms.The preparation is achieved by choosing an appropriate (in general entangled)initial state of the atomic sequence,and does neither require a final state measurement of the atoms,nor a control of the atom-field interaction.Furthermore,the method is applicable also when starting from mixed initial field states. We show how to determine the optimal initial atomic state which pre- pares the desired field state with the maximum fidelity,and prove the feasibility of our state preparation method by numerical calculations. In the second part,we demonstrate the noise-induced control of quantum jumps in a fundamental open quantum system.Here,in addition to the subsequent interaction with a flux of two-level atoms,the quantized field is also coupled to a thermal environment.Under certain experimental conditions,the photon field exhibits a bistable behavior,with quantum jumps between two metastable states.In the presence of a small peri- odic signal (i.e.,a modulation of the initial state of the two-level atoms crossing the single-mode resonator),the best synchronization of these quantum jumps with the signal is achieved at an optimal,nonvanishing temperature of the environment.This stochastic resonance e ffect can be observed in di fferent components of the atomic Bloch vector on exit from the cavity. The third part treats a speci fic problem concerning the characterization of entanglement between two quantum mechanical two-level systems. We consider the optimal decomposition of a two-qubit state into an en- tangled and a separable part,with maximal weight of the latter,and derive necessary and su fficient conditions for the optimality of the de- composition.","abstract_has_math":false,"creators":["Wellens, Thomas"],"institution":"Ludwig-Maximilians-Universität","degree_name":null,"degree_level":"thesis.doctoral","degree_discipline":null,"degree_department":null,"school":null,"contributors":[],"advisors":[],"committee_chairs":[],"committee_members":[],"year":2002,"date_issued":"2002-05-03","date_published":"2002-05-03","updated_at":"2026-07-24T02:51:21Z","subjects":[],"languages":[],"rights":[],"rights_urls":[],"identifier_entries":[]},"links":{"outbound_url":"https://edoc.ub.uni-muenchen.de/81/","outbound_label":"Repository record","outbound_source":"source_url"},"metadata_groups":[{"id":"people","label":"People","entries":[{"key":"dc:creator","label":"Author","values":["Wellens, Thomas"]}]},{"id":"academic_context","label":"Academic Context","entries":[{"key":"dc:publisher","label":"Institution","values":["Universitätsbibliothek der Ludwig-Maximilians-Universität"]},{"key":"dc:type","label":"Dc Type","values":["doctoralThesis"]},{"key":"thesis:degree_level","label":"Degree Level","values":["thesis.doctoral"]},{"key":"thesis:institution_name","label":"Thesis Institution Name","values":["Ludwig-Maximilians-Universität"]}]},{"id":"additional","label":"Additional Metadata","entries":[{"key":"dc:description.abstract","label":"Abstract","values":["In the first part of this thesis,we examine the preparation of a single- mode radiation field in arbitrary pure quantum states via resonant inter- action with a sequence of two-level atoms.The preparation is achieved by choosing an appropriate (in general entangled)initial state of the atomic sequence,and does neither require a final state measurement of the atoms,nor a control of the atom-field interaction.Furthermore,the method is applicable also when starting from mixed initial field states. We show how to determine the optimal initial atomic state which pre- pares the desired field state with the maximum fidelity,and prove the feasibility of our state preparation method by numerical calculations. In the second part,we demonstrate the noise-induced control of quantum jumps in a fundamental open quantum system.Here,in addition to the subsequent interaction with a flux of two-level atoms,the quantized field is also coupled to a thermal environment.Under certain experimental conditions,the photon field exhibits a bistable behavior,with quantum jumps between two metastable states.In the presence of a small peri- odic signal (i.e.,a modulation of the initial state of the two-level atoms crossing the single-mode resonator),the best synchronization of these quantum jumps with the signal is achieved at an optimal,nonvanishing temperature of the environment.This stochastic resonance e ffect can be observed in di fferent components of the atomic Bloch vector on exit from the cavity. The third part treats a speci fic problem concerning the characterization of entanglement between two quantum mechanical two-level systems. We consider the optimal decomposition of a two-qubit state into an en- tangled and a separable part,with maximal weight of the latter,and derive necessary and su fficient conditions for the optimality of the de- composition.","Im ersten Teil der vorliegenden Arbeit untersuchen wir die Pr ¨aparation einer einzelnen Mode des quantisierten Strahlungsfeldes in einen beliebi- gen Quantenzustand durch resonante Wechselwirkung mit einer Reihe von Zwei-Niveau-Atomen.Die Pr ¨aparation erfolgt durch Wahl eines geeigneten (im allgemeinen verschr ¨ankten)Anfangszustands der Atome, und ben ¨otigt weder eine Messung des atomaren Endzustands,noch eine Kontrolle der Atom-Feld-Wechselwirkung.Dieses Verfahren ist auch bei gemischten Anfangszust ¨anden des Feldes anwendbar.Wir erl ¨autern, wie man den optimalen atomaren Anfangszustand au ffinden kann, welcher den gew ¨unschten Feldzustand mit maximaler G ¨ute erzeugt, und zeigen durch numerische Berechnungen die Umsetzbarkeit unseres Pr ¨aparationsverfahrens. Im zweiten Teil demonstrieren wir die rauschinduzierte Kontrolle von Quantenspr ¨ungen in einem fundamentalen o ffenen Quantensystem. Neben der Wechselwirkung mit einem Fluss aufeinanderfolgender Zwei- Niveau-Atome ist das Feld hierbei auch an eine thermische Umgebung gekoppelt.Bei bestimmter Wahl der experimentellen Parameter wird das Photonenfeld bistabil und vollzieht Quantenspr ¨unge zwischen zwei metastabilen Zust ¨anden.In der Gegenwart eines schwachen,periodi- schen Signals (d.h.einer Modulation des Anfangszustandes der den Resonator durchquerenden Zwei-Niveau-Atome)wird die beste Synchro- nisierung der Quantenspr ¨unge mit diesem Signal bei einer optimalen, nichtverschwindenden Temperatur der Umgebung erzielt.Dieser Ef- fekt der stochastischen Resonanz ist in verschiedenen Komponenten des Blochvektors nach Austritt der Atome aus dem Resonator beobachtbar. Der dritte Teil behandelt ein spezielles Problem in der Charakterisierung von Verschr ¨ankung zwischen zwei quantenmechanischen Zwei-Niveau- Systemen.Wir betrachten die optimale Zerlegung eines Zustands zweier Qubits in einen verschr ¨ankten und einen separablen Anteil,wobei das Gewicht von letzterem maximiert wird,und leiten notwendige und hin- reichende Bedingungen f ¨ur die Optimalit ¨at der Zerlegung her."]},{"key":"dc:format.medium","label":"Dc Format Medium","values":["application/pdf"]},{"key":"dc:title","label":"Title","values":["Entanglement and control of quantum states"]}]}],"canonical_facts":{"dc:creator":["Wellens, Thomas"],"dc:description.abstract":["In the first part of this thesis,we examine the preparation of a single- mode radiation field in arbitrary pure quantum states via resonant inter- action with a sequence of two-level atoms.The preparation is achieved by choosing an appropriate (in general entangled)initial state of the atomic sequence,and does neither require a final state measurement of the atoms,nor a control of the atom-field interaction.Furthermore,the method is applicable also when starting from mixed initial field states. We show how to determine the optimal initial atomic state which pre- pares the desired field state with the maximum fidelity,and prove the feasibility of our state preparation method by numerical calculations. In the second part,we demonstrate the noise-induced control of quantum jumps in a fundamental open quantum system.Here,in addition to the subsequent interaction with a flux of two-level atoms,the quantized field is also coupled to a thermal environment.Under certain experimental conditions,the photon field exhibits a bistable behavior,with quantum jumps between two metastable states.In the presence of a small peri- odic signal (i.e.,a modulation of the initial state of the two-level atoms crossing the single-mode resonator),the best synchronization of these quantum jumps with the signal is achieved at an optimal,nonvanishing temperature of the environment.This stochastic resonance e ffect can be observed in di fferent components of the atomic Bloch vector on exit from the cavity. The third part treats a speci fic problem concerning the characterization of entanglement between two quantum mechanical two-level systems. We consider the optimal decomposition of a two-qubit state into an en- tangled and a separable part,with maximal weight of the latter,and derive necessary and su fficient conditions for the optimality of the de- composition.","Im ersten Teil der vorliegenden Arbeit untersuchen wir die Pr ¨aparation einer einzelnen Mode des quantisierten Strahlungsfeldes in einen beliebi- gen Quantenzustand durch resonante Wechselwirkung mit einer Reihe von Zwei-Niveau-Atomen.Die Pr ¨aparation erfolgt durch Wahl eines geeigneten (im allgemeinen verschr ¨ankten)Anfangszustands der Atome, und ben ¨otigt weder eine Messung des atomaren Endzustands,noch eine Kontrolle der Atom-Feld-Wechselwirkung.Dieses Verfahren ist auch bei gemischten Anfangszust ¨anden des Feldes anwendbar.Wir erl ¨autern, wie man den optimalen atomaren Anfangszustand au ffinden kann, welcher den gew ¨unschten Feldzustand mit maximaler G ¨ute erzeugt, und zeigen durch numerische Berechnungen die Umsetzbarkeit unseres Pr ¨aparationsverfahrens. Im zweiten Teil demonstrieren wir die rauschinduzierte Kontrolle von Quantenspr ¨ungen in einem fundamentalen o ffenen Quantensystem. Neben der Wechselwirkung mit einem Fluss aufeinanderfolgender Zwei- Niveau-Atome ist das Feld hierbei auch an eine thermische Umgebung gekoppelt.Bei bestimmter Wahl der experimentellen Parameter wird das Photonenfeld bistabil und vollzieht Quantenspr ¨unge zwischen zwei metastabilen Zust ¨anden.In der Gegenwart eines schwachen,periodi- schen Signals (d.h.einer Modulation des Anfangszustandes der den Resonator durchquerenden Zwei-Niveau-Atome)wird die beste Synchro- nisierung der Quantenspr ¨unge mit diesem Signal bei einer optimalen, nichtverschwindenden Temperatur der Umgebung erzielt.Dieser Ef- fekt der stochastischen Resonanz ist in verschiedenen Komponenten des Blochvektors nach Austritt der Atome aus dem Resonator beobachtbar. Der dritte Teil behandelt ein spezielles Problem in der Charakterisierung von Verschr ¨ankung zwischen zwei quantenmechanischen Zwei-Niveau- Systemen.Wir betrachten die optimale Zerlegung eines Zustands zweier Qubits in einen verschr ¨ankten und einen separablen Anteil,wobei das Gewicht von letzterem maximiert wird,und leiten notwendige und hin- reichende Bedingungen f ¨ur die Optimalit ¨at der Zerlegung her."],"dc:format.medium":["application/pdf"],"dc:publisher":["Universitätsbibliothek der Ludwig-Maximilians-Universität"],"dc:title":["Entanglement and control of quantum states"],"dc:type":["doctoralThesis"],"thesis:degree_level":["thesis.doctoral"],"thesis:institution_name":["Ludwig-Maximilians-Universität"]},"updated_at":"2026-07-24T02:51:21Z"}