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Title of Thesis

Sajid Qamar
Institute/University/Department Details
Department of Electronics/ Quaid-i-Azam University Islamabad
Number of Pages
Keywords (Extracted from title, table of contents and abstract of thesis)
single atom localization, localization schemes, autler-townes microscopy, b eigensystem

Entanglement of the atom and field leads towards the measurement of the state of the atom or field depending on the kind of measurement made. Taking advantage of this fact, we propose spectroscopic methods for the single atom localization within the subwavelength domain of the optical standing wave field.

When a two-level atom interacts with some intense radiation field the spectrum of the scattered light signal exhibits a three-peak Mollow spectrum. We propose a scheme of atom localization based on the resonance fluorescence from a two-level atom interacting with a standing wave field. The Rabi frequency is considered to be position dependent and therefore, the spontaneously emitted photon carries the information about the center-of-mass motion of the atom. This leads to the localization of the single atom by measuring the frequency of the spontaneously emitted photon even during the passage of the atom through the standing wave field. We predict a spatial resolution in position information of up to λ/60 where λ is the optical wavelength.

Detuning of the coherent field with the atomic transition plays an important role in the characterization of the peaks present in the Autler- Townes spectrum of a three-level atom. Strong line narrowing is observed in one of the peaks of the Autler- Townes doublet depending on the choice of the detuning. We investigate how this detuning effects the position information of the atom inside the standing wave field in upper-level and lower-level coupling schemes of Autler- Townes microscopy. We show an enhancement in precision position measurement by factor of at least 4 in upper-level coupling scheme due to the quantum interference phenomenon. This enhancement is not observed in lower-level coupling scheme where the quantum interference is not taking place.

We also consider a system where a three-level atom is interacting with a monochromatic radiation field in such a way that the decay takes place from upper level to the intermediate level with a rate T and from intermediate level to lower level at a rate γ. This type of system exhibits a non stationary scattered light signal. We report the results of the spontaneous emission spectrum for non stationary scattered light signal by using the definition of time-dependent physical spectrum. This is a rare example of problems where time-dependent physical spectrum can be calculated exactly. We study the characteristics of the spontaneous spectrum for a resonant and off-resonant case and show that this physical spectrum recovers the results of earlier work quite successfully. We also show that the decay rate r disturbs the atomic coherence and finally eliminates the dark line from the center of the spontaneous spectrum. Here we only consider upper-level coupling case for the time-dependent spontaneous spectrum because in lower-level coupling case the system automatically evolved a pumping mechanism due to the coupling of ground level to the upper level via radiation field. Thus a steady-state limit exists in lower-level coupling scheme.

We investigate the phenomenon of atom localization by using the non stationary Autler-Townes microscopy. The decay rate T reduces the precision in position measurement which is consistent with the results of the non stationary spontaneous emission spectrum. This is due to the fact that for the upper-level coupling case, the standing wave field is coupled to atomic transition and it induces a coherence in the upper-level atomic transition but the spontaneous decay from the upper level to the intermediate level disturbs this coherence. When the effect of the spontaneous decay dominates the coherence effect the quantum interference phenomenon vanishes and thus the precision in localization reduces.

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2364.11 KB
S. No. Chapter Title of the Chapters Page Size (KB)
1 0 Contents
179.2 KB
2 1 Introduction 3
409.72 KB
  1.1 Atom Localization Using Mechanical Methods 5
  1.2 Atom Localization Using Optical Methods 6
  1.3 Physical Picture Of Present Localization Schemes 12
  1.4 Outline 15
3 2 A Brief History Of Radiation-Matter Interaction 16
176.48 KB
  2.1 Atom- Field Interaction For Two-Level System 17
  2.2 Atom-Filed Interaction For Multi-Level System 19
4 3 Atom Localization Via Resonance Fluorescence 22
363.01 KB
  3.1 Model And Equations 23
  3.2 Probability For Single Photon Excitation 30
  3.3 Results And Discussion 32
5 4 Autler-Townes Microscopy 38
447.3 KB
  4.1 Model 40
  4.2 The Upper-Level Coupling Case 40
  4.3 The Lower-Level Coupling Case 47
  4.4 Results And Discussion 50
6 5 Time-Dependent Spectrum Of Three-Level Atoms 58
874.77 KB
  5.1 Background Of The Time-Dependent Physical Spectrum 59
  5.2 Model 61
  5.3 Quantum Interference And Coherence Phenomena 72
  5.4 Single Atom Localization 84
  5.5 A Resonance Fluorescence Spectrum For Stationary Case 84
  5.6 B Eigensystem Of Matrix M 1 And M 2 92