Creation and Detection of Single Photons Creation and Detection of Single Photons Hatim Azzouz Thesis for the degree of Doctor of Philosophy in Physics c Hatim Azzouz, Stockholm 2016 ISBN 978-91-7649-342-7 Printed in Sweden by Universitetsservice US-AB, Stockholm, Stockholm 2016 Distributor: Department of Physics, Stockholm University Cover illustration: Red fluorescence from Rhodamine 6G excited at 532 nm with the green confocal microscope. "The saddest aspect of life right now is that science gathers knowledge faster than society gathers wisdom." Isaac Asimov Abstract A growing number of technologies employ quantum properties in order to produce solutions that surpass the performance of conventional devices, or to execute operations that are fundamentally impossible with classical sys- tems alone. In the field of optical quantum information science, photons are utilized to encode, communicate and manipulate information, making them vitally important. While photon production always constitutes the first step in any optical experiment, in the field of quantum information science, the recording of data through the process of photon detection is an equally crucial final step. This thesis deals with both the single photons generation (based on diamond color defects) and their detection, utilizing a novel type of superconducting detectors. In particular, part one of this thesis is devoted to the construction of custom-designed microscope setup, and the development of laboratory experi- ments, to enable the generation of single photons as well as the investigation of the optical and spin properties of diamond color centers. Confocal microscopy is used for this purpose, as it allows for the identification and addressing of in- dividual color centers that emit only single photons. This microscope also fea- ture an integrated self-built microwave and magnetic hardware setup, which allows for a wide range of spin environment spectroscopy studies. Single pho- ton emission is demonstrated through both photon anti-bunching and Rabi oscillations at room temperature. The second part of the thesis offers an exploration of superconducting single photon detectors through experiment. Since electronics are an essential part of these detectors, the possibility of using a novel alternative scheme based on capacitive readout combined with fast gating to enable simplified readout is demonstrated. This scheme overcomes the limitations of conventional readout schemes, which require large bandwidth amplification and complex counting electronics. Besides photon detection, the capabilities of these detectors are also expanded to include high-energy particles in the MeV energy range, and the detectors are demonstrated to not only detect single a- and b-particles, but to do so with near unity efficiency. Finally, a multipurpose testing station for superconducting detectors is demonstrated with a central objective of optimizing the coupling efficiency of light to the active area of the detector, as well as to allow for a fast exchange of the optical fiber, thereby facilitating an efficient characterization of the detector. The optimization of this coupling efficiency was demonstrated through proof-of-principle experiments. Contents Sammanfattning på svenska ................................ vii List of accompanying papers ................................ viii Part I: Preface 1 Introduction .......................................... 3 1.1 Background and motivation................................... 3 1.2 Ideal single photon sources.................................. 4 1.3 Ideal single photon detectors................................. 6 1.4 Thesis outline............................................ 7 1.5 My contributions.......................................... 10 1.6 Acknowledgments......................................... 11 Part II: Single Photon sources 2 Intensity fluctuation statistics .............................. 15 2.1 Classical description of light.................................. 16 2.1.1 Poissonian photon statistics.............................. 16 2.1.2 Classical second-order correlation function.................... 17 2.2 Quantum description of light.................................. 18 2.2.1 Hanbury Brown-Twiss setup for photons...................... 18 2.2.2 Quantized second-order correlation function................... 19 2.2.3 Photon bunching and antibunching.......................... 20 2.2.4 Is antibunched light the same as sub-Poissonian light?............ 22 3 Nitrogen-vacancy centers in diamond........................ 23 3.1 Synthesis and generation of NV defects.......................... 24 3.2 Zero phonon line and phonon sideband.......................... 25 3.3 Physical structure......................................... 26 3.4 Electronic structure........................................ 27 3.5 Spin manipulation and readout................................ 30 3.5.1 Optical spin polarization and spin-dependent florescence.......... 30 3.5.2 Magnetic single spin manipulation.......................... 31 3.5.3 CW microwave experiments.............................. 32 3.5.4 Pulsed microwave experiments............................ 32 4 Confocal Microscopy .................................... 39 4.1 Principle of Operation...................................... 40 4.2 Optical components........................................ 42 4.2.1 Laser source as illumination.............................. 43 4.2.2 Lens objectives....................................... 43 4.2.3 Optical fibers......................................... 44 4.2.4 Other optical components................................ 45 4.3 Optical considerations and design requirements.................... 46 4.3.1 Light diffraction and resolution............................. 46 4.3.2 Optical sectioning and pinhole size.......................... 49 4.3.3 The optical fiber as a pinhole.............................. 51 4.4 Detection and control electronics............................... 52 4.4.1 Detection and readout software............................ 52 4.4.2 Positioning systems and scanning software.................... 53 4.4.3 Auto-correlator and coincidence unit......................... 53 4.5 Implementation and experimental setup.......................... 54 4.5.1 The green confocal setup................................ 54 4.5.2 The red confocal setup.................................. 59 4.6 Beyond confocal microscopy - STED microscopy.................... 62 4.6.1 Principle of operation................................... 63 4.6.2 Implementation....................................... 65 5 Spin manipulation and readout setup ........................ 67 5.1 Microwave and magnetic hardware setup......................... 67 5.2 Double-pass acousto-optic modulator setup....................... 68 5.3 Integrated setup and timing control............................. 71 6 Experimental results - NV center characterization .............. 73 6.1 Diamond sample preparation................................. 73 6.2 Confocal scans of NV centers................................. 74 6.3 Optical fluorescence spectrum................................ 77 6.4 Demonstration of antibunching................................ 77 6.5 Demonstration of Rabi oscillations.............................. 79 Part III: Superconducting Single Photon Detectors 7 Background and basic concepts............................ 85 7.1 Superconductivity and working principle of SSPDs................... 85 7.1.1 Superconductivity..................................... 85 7.1.2 Energy gap.......................................... 85 7.1.3 Phase transition and resistance............................ 86 7.1.4 Microscopic absorption model............................. 88 7.1.5 Hotspot formation..................................... 89 7.1.6 Phenomenological model................................ 92 7.2 Quantification of the performance of an SSPD...................... 93 7.2.1 Detection efficiency.................................... 94 7.2.2 Dead time........................................... 97 7.2.3 Dark counts......................................... 98 7.2.4 Timing jitter.......................................... 99 8 SSPD design and measurement setup....................... 101 8.1 Design and fabrication requirements............................ 101 8.1.1 Particle absorption..................................... 102 8.1.2 Advantages of a nano-structured superconductor................ 103 8.1.3 NbTiN on silicon - an alternative to the NbN on sapphire-based SSPD. 104 8.1.4 Fabrication.......................................... 104 8.2 Readout electronics and experimental setup....................... 107 8.2.1 Measurement setup.................................... 107 8.2.2 Characterization...................................... 108 9 Capacitive readout and gating of the SSPD ................... 111 9.1 Introduction............................................. 111 9.2 Capacitive readout scheme.................................. 111 9.3 Gating behavior.......................................... 115 9.4 Conclusion.............................................. 119 10 High-energy particle detection ............................. 121 10.1 Introduction............................................. 121 10.2 Sample preparation........................................ 122 10.3 Sample mounting and setup................................. 123 10.4 Particle detection......................................... 125 10.5 Conclusion.............................................. 129 11 A multi-purpose