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From coherent to single-particle quantum walks / vorgelegt von Thomas Nitsche ; [1. Gutachterin: Prof. Dr. Christine Silberhorn, 2. Gutachter: Prof. Dr. Thomas Zentgraf]. Paderborn, 2019
Content
Abstract
Zusammenfassung
Introduction
Fundamentals Part 1: Parametric Down-Conversion
Fundamentals Part 2: Quantum Walks
Random Walk vs. Quantum Walk
Continuous-time vs. Discrete-time Quantum Walk
Coin vs. Step Operation
Fundamentals Part 3: Experimental Signatures of a Single Photon
Second-order Correlations Measurements
HOM-Dip Experiment
State of the Art
Interest in Quantum Walks
Implementations of Quantum Walks
Figures of Merit
From Coherent Quantum Walks to Single Photon Quantum Walks
Towards Boson Sampling
Experimental Setup
Time Multiplexing
State Preparation
Time-multiplexed Pump
PDC Crystal
Evolution
Dynamic Switchings - Electronics
Dynamic Switchings - Pockels Cells
Detection
Possible Measurement Times
Achievable Rates
Comparison with Quantum Dot Source
Photon-number Resolution
Conclusion
Optimising HOM-Dip Visibility
HOM-Dip Experiment between Different Time Bins
Temporal Delay
Fluctuations introduced by the Pump Laser
Fluctuations introduced by the Fibres
Temporal Shape - Dispersion
Spectral Characteristics
PDC in LN sample
PDC in KTP sample
PDC in Sample 2
Spectral Distinguishability
Spectral Purity
PDC in Sample 2
Photon-Number Statistics
Numerical Simulations in Framework QuTip
Mean Photon Number
Losses
Measured Visibilities - Results and Conclusion for Sample 1
Conclusion and Results for Sample 2
Testing Loop with seeded PDC
Experiments with Coherent States Part 1: Investigating Topological Phenomena
Introduction
Split-step Quantum Walk and Topological Invariants
Scattering Approach
Experimental Implementation of the Scattering Approach
Results for the Scattering Approach
Topological Phase Transitions
Robustness against Disorder
Emergence of Edge States
Measuring Eigenvalues of Edge States
Decoupling
Eigenstate Distillation
Phase-Reference Method
Evolution of the Wave Function
Experimental Eigenvalues
Supersymmetric Polarisation Anomaly
Midgap States with Anomalous Polarisation
Experimental Investigation of Midgap States
Conclusion: Accessibility of Topological Properties
Experiments with Coherent States Part 2: Investigating Measurement-induced Effects
Recurrence
Reset and Continual Scheme
Walker's Evolution with Projective Measurements
Experimental Implementation
Time-multiplexed HOM-Dip
Probing Parity
Probing Relative Translation
Higher Numbers of Time Bins
Simulating Time-multiplexed HOM-Dip with QuTip
Time-multiplexed HOM-Dip with Coherent Light
Mean Photon Number
EOM Beam Splitter Angle
QWP Beam Splitter Angle
Imbalanced Losses
Effects of Partial Overlap
Experimental Investigation of Imperfections
Conclusion for Time-multiplexed HOM-dip
Conclusion and Outlook
Experiments with Coherent Quantum Walks
Experiments with Quantum States
Bibliography
Acknowledgements
Appendix: Equivalence of Coherent Light and Single Photons for a Single Initial Position
Appendix: Parity of Interfering State
Interfering State with Even Parity
Interfering State with Odd Parity
Appendix: Processing Time Lists
Appendix: Software in Use
Accessing EOMs
Generating Time Lists for the EOMs
Data Analysis - Analysing histograms from bin-files
Data Analysis - Live analysis of Coincidences
Numerical Simulations in QuTip
Appendix: The Pump
Appendix: Implementing Seeded PDC
Appendix: Equivalence of Split-step Definitions
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