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Observation of an exceptional point in an ultrasonic cavity : 초음파 공진기에서의 예외점 관측
DC Field | Value | Language |
---|---|---|
dc.contributor.advisor | 안경원 | - |
dc.contributor.author | 신영훈 | - |
dc.date.accessioned | 2017-10-27T17:10:58Z | - |
dc.date.available | 2017-10-27T17:10:58Z | - |
dc.date.issued | 2017-08 | - |
dc.identifier.other | 000000145741 | - |
dc.identifier.uri | https://hdl.handle.net/10371/137131 | - |
dc.description | 학위논문 (박사)-- 서울대학교 대학원 자연과학대학 물리·천문학부, 2017. 8. 안경원. | - |
dc.description.abstract | A physical system can be described by a non-Hermitian Hamiltonian if the system is open or it has either absorptive loss or amplifying gain. One of the important properties of the non-Hermitian Hamiltonian is the existence of an exceptional point (EP). This EP condition is satisfied when the coupling strength between interacting eigenstates is the same as their differential loss. At an EP, the eigenstates are degenerate in both eigenvalue and eigenfunction, exhibiting interesting features such as branch-point topology, breakdown of adiabaticity when encircled dynamically.
In this thesis, we reveal EP's both in ultrasonic and optical cavities, both of which are non-Hermitian systems. First we report observation of an EP in an ultrasonic cavity both theoretically and experimentally. Concentric circular shell cavity is adopted as platform for the study. At first, system parameters for the EP condition is predicted by theoretical analysis. The schlieren method, which is widely used to visualize refractive index modulation in transparent media, is applied to the ultrasonic cavity when we experimentally measure the resonance spectrum and the wavefunction. Then we confirm the existence of an EP in the shell cavity by comparing the theoretical and experimental results. We also investigate modified spontaneous emission in a deformed optical microcavity, which is known as the Petermann effect. First we establish non-Hermitian cavity quantum electrodynamics (QED) theory, deriving modified laser rate equations. Then we find out that number of spontaneously emitted photon into a mode can be enhanced by the Petermann effect near an EP, whereas total atomic spontaneous emission rate is invariant. As a consequence, it is shown that the emission power of a lasing mode can be increased at the same pump power compared to that without the Petermann effect. Finally, we also present experimental results supporting the non-Hermitian cavity-QED theory. | - |
dc.description.tableofcontents | 1 Introduction 1
2 EP in an ultrasonic cavity 4 2.1 Theoretical study 5 2.1.1 Variables and boundary conditions 5 2.1.2 Model system: Concentric shell cavity 7 2.1.3 Equations of the system and finding resonances 10 2.1.4 Two resonant mode groups: FBM and SBM 15 2.1.5 Mode interaction between FBM and SBM 17 2.1.6 Transition between MC and AC - Existence of an EP 20 2.1.7 Locating an exact EP 23 2.2 Experimental verification 24 2.2.1 Introduction to schlieren method 24 2.2.2 Experimental setup 27 2.2.3 Measurement of the resonances and their wavefunction 30 2.2.4 Experimental observation of an EP 33 2.3 Schlieren method in a transparent shell cavity 38 3 EP in a deformed dielectric microcavity 45 3.1 Quantum theory of spontaneous emission in non-Hermitian system 47 3.1.1 Hermitian vs. non-Hermitian system 47 3.1.2 Petermann factor in quantum mechanics 48 3.1.3 Photon number operator 50 3.1.4 Interaction Hamiltonian between cavity field and atom 51 3.1.5 Quantum Langevin equation 52 3.1.6 Modified laser rate equations 55 3.2 Two-dimensional microcavity 57 3.2.1 Optical microcavity 58 3.2.2 Identifying adjoint in a two-dimensional microcavity 62 3.2.3 Deformed microcavity 63 3.2.4 Boundary element method 64 3.2.5 Deformation-tunable quadru-octapolar cavity 69 3.3 Divergent Petermann factor and power enhancement near EP's of microcavities 70 3.4 Experimental verification 82 3.4.1 Experimental setup 82 3.4.2 Grouping modes and mode dynamics 85 3.4.3 Identification of the system parameters 89 3.4.4 Experimental results 90 3.4.5 Theoretical modeling and discussion 99 4 Conclusion 102 | - |
dc.format | application/pdf | - |
dc.format.extent | 12927301 bytes | - |
dc.format.medium | application/pdf | - |
dc.language.iso | en | - |
dc.publisher | 서울대학교 대학원 | - |
dc.subject | exceptional point | - |
dc.subject | ultrasonic cavity | - |
dc.subject | schlieren method | - |
dc.subject | deformed microcavity | - |
dc.subject | fluorescence spectroscopy | - |
dc.subject | enhanced spontaneous emission rate | - |
dc.subject | Petermann factor | - |
dc.subject.ddc | 523.01 | - |
dc.title | Observation of an exceptional point in an ultrasonic cavity | - |
dc.title.alternative | 초음파 공진기에서의 예외점 관측 | - |
dc.type | Thesis | - |
dc.contributor.AlternativeAuthor | Younghoon Shin | - |
dc.description.degree | Doctor | - |
dc.contributor.affiliation | 자연과학대학 물리·천문학부 | - |
dc.date.awarded | 2017-08 | - |
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