Thesis (Ph.D.)--Michigan State University. Dept. of Electrical and Computer Engineering, 2008. / Title from PDF t.p. (viewed on July 23, 2009) Includes bibliographical references (p. 177-181). Also issued in print.

Superconducting single-photon detectors (SSPDs) are the leading detectors in terms of high-speed single-photon counting and high detection efficiency (DE). One factor that limits the DE is the critical current Ic, which is the maximum current before the superconductor switches to the normal state. Increasing device’s bias current towards the Ic can improve the DE. However, the device’s Ic is reduced due to constriction and current crowding at the edges of the wire. Typically, this is caused by fabrication defects. Locally suppressing superconductivity at these defects can potentially lessen the occurrence of current crowding. In this thesis, we used the beam from the helium ion microscope (HIM) and measured the Ic to observe the effects of locally irradiating specific areas on a SSPD wire. Due to the HIM’s small spot size and high collimation, we can control the superconducting gap precisely at the center and edges of the wire. Suppressing the edges can potentially reduce current crowding and increase the device’s critical current while suppressing the center can improve detection sensitivity for photons incident at that location. Our results showed that the irradiated devices had reduced Ic compared to unirradiated devices for both cases. We then extend this method of local suppression of superconductivity to explore an alternative method of fabricating SSPDs by directly writing the device on the superconducting thin film. This can enable the fabrication of devices without the use of lithography resist. In our experiment, we fabricated a 3 μm wire using optical lithography that was disconnected at the center and connected it by writing a single 1 μm wire with the He+ ion beam. We measured the Ic for samples with and without the 1 μm wire pattern and observed that the Ic decreased as we increased the ion dose. Overall, this work aims to contribute to the continuing investigation of the detection mechanism for SSPDs and the improvement of nanofabrication methods using the HIM.

LHCb is an experiment designed to make precision measurements of Charge- Parity violation in the B meson system. We report a measurement of the B± crosssection and production asymmetry, using B± → J/u K± decays collected at the LHCb detector in 2010 and 2011. Using 27.6 pb-1 of pp collisions at a centre-of-mass energy 7 TeV, we obtain a B± cross-section of [41.6 ± 0.6 (stat.) ± 3.0 (sys.) ± 4.2 (lumi.)] μb in the rapidity region 2 to 4.5. Using 371.1 pb-1 of pp collisions at a centre-of-mass energy 7 TeV, we obtain a B± production asymmetry of [-2.09 ± 1.20 ± 0.8 (CP) ]% in the same rapidity region. The Ring Imaging Cherenkov system of LHCb uses Hybrid photon detectors (HPDs) for single photon detection. This thesis summarises the use of ion feedback measurements as indicators of HPD vacuum quality.

The Large Hadron Collider started operation this year, 2008. LHCb is a precision heavy-flavour experiment at this collider. The precision of LHCb is greatly aided by the LHCb Ring Imaging Cherenkov system for the separation and identification of charged hadrons. This system uses pixel Hybrid Photon Detectors, an innovative new technology for single photon imaging. The simulation and testing of these photon detectors are reported and discussed. The photodetectors were measured to have reached or exceeded the specifications in key areas. In particular, the detector quantum efficiencies far exceed expectations, by a relative 27 %. The precision of LHCb will be used to examine CP-violation and rare decays of B-mesons. A key part of the physics programme will be a measurement of the CP-violating flavour specific asymmetry in neutral B-meson mixing. This asymmetry is expected to be very small in the Standard Model, of order 10-4, however it is very sensitive to new physics, which can increase the asymmetry dramatically. We present an improved event selection and a novel method to control systematics. This will enable us to make a world-leading measurement of this parameter in one nominal year of data taking (2 fb-1).

LHCb is a high-precision experiment for the study of CP violation and rare decays in B physics. It has two Ring Imaging Cherenkov (RICH) counters for particle identification. The RICH system uses Hybrid Photon Detectors (HPD) for single photon detection. This thesis describes tests performed on individual HPDs for quantum efficiency and vacuum quality. It then presents work done monitoring HPD vacuum quality through regular ion feedback measurements after they were mounted into the RICH. Also discussed is HPD vacuum degradation and how replacement and repair of deteriorated HPDs was implemented using data from the vacuum monitoring. Preparations for an upgrade to LHCb have started. The upgrade will extend the discovery potential of the LHCb by increasing the rate of data collection. This thesis presents particle identification and avour tagging studies using upgrade simulations. Flavour tagging using kaons was then reoptimised for upgrade conditions and this work is described with discussions of the results.

Building complex quantum systems has the potential to reveal phenomena that cannot be studied using classical simulation. Photonics has proven to be an effective test-bed for the investigation of such quantum-enhanced technologies, however, the proliferation of bulk optical components is unlikely to be a scalable route towards building more complex devices. Instead, the miniaturisation, inherent phase stability and trivial alignment afforded by integrated photonic systems has been shown to be a promising alternative. In the first half of this thesis, we describe experiments exploiting the quantum interference of three single photons on a reconfigurable integrated photonic chip. We develop a low-loss source of single photons and introduce a low-loss silica-on-silicon waveguide architecture which enables us to show the first genuine quantum interference of three single photons on an integrated platform. A loss-tolerant, element-wise characterisation scheme is developed along with a statistical test to verify that this multi-photon circuit behaves as expected. We then make use of this three-photon interference to detail the first proof-of-principle demonstration of a new intermediate model of quantum computation called boson sampling. Finally, we perform an on-chip demonstration of the quantum teleportation protocol where all key parts --- entanglement preparation, Bell-state analysis and quantum state tomography --- are performed on a reconfigurable photonic chip. The element-wise characterisation scheme developed earlier is shown to be critical to mitigate fabricated component errors. We develop a theoretical model to account for all sources of possible error in the circuit and find good agreement with the measured teleported state fidelities, which exceed the average teleportation fidelity possible with a classical device. We identify the elements of this error budget relevant to scaling and propose improvements to chip characterisation and fabrication in order to achieve high fidelity operation. In the second half, we discuss the use of high efficiency superconducting transition edge sensors in enabling quantum experiments using more photons. We detail the installation and characterisation of these detectors in a new lab in Oxford. We achieve good photon number-resolution and high-efficiency operation. Work to integrate these detectors on the silica-on-silicon waveguide architecture is discussed and we detail the optical and thermal device modelling performed to optimise the on-chip detection efficiency. New, on-chip detectors, fabricated according to this design are shown to operate as expected and achieve high-efficiency and good energy resolution.

The market for higher data rate communication is driving the semiconductor industry to develop new techniques of writing at smaller scales, while continuing to scale bandwidth at low power consumption. The question arises of how to continue to sustain this trend. Silicon photonic (SiPh) devices offer a potential solution to the electronic interconnect bandwidth bottleneck. SiPh leverages the technology commensurate of decades of fabrication development with the unique functionality of next-generation optical interconnects. Finer fabrication techniques have allowed for manufacturing physical characteristics of waveguide structures that can support multiple modes in a single waveguide. By refining modal characteristics in photonic waveguide structures, through mode multiplexing with the asymmetric y-junction and microring resonator, higher aggregate data bandwidth is demonstrated via various combinations of spatial multiplexing, broadening applications supported by the integrated platform. The main contributions of this dissertation are summarized as follows. Experimental demonstrations of new forms of spatial multiplexing combined together exhibit feasibility of data transmission through mode-division multiplexing (MDM), mode-division and wavelength-division multiplexing (MDM-WDM), and mode-division and polarization-division multiplexing (MDM-PDM) through a C-band, Si photonic platform. Error-free operation through mode multiplexers and demultiplexers show how data can be viably scaled on multiple modes and with existing spatial domains simultaneously. This work opens up new avenues for scaling bandwidth capacity through leveraging orthogonal domains available on-chip, beyond what had previously been employed like WDM and time-division multiplexing (TDM). Furthermore, we explore expanding device channel support from two to three arms. Finding that a slight mismatch in the third arm can increase crosstalk contributions considerably, especially when increasing data rate, we explore a methodical way to design the asymmetric y-junction device by considering its angles and multiplexer/demultiplexer arm width. By taking into consideration device fabrication variations, we turn towards optimizing device performance post-fabrication. Through ModePROP simulations, optimizing device performance dynamically post-fabrication is analyzed, through either electro-optical or thermo-optical means. By biasing the arm introducing the slight spectral offset, we can quantifiably improve device performance. Scaling bandwidth is experimentally demonstrated through the device at 3 modes, 2 wavelengths, and 40 Gb/s data rate for 240 Gb/s aggregate bandwidth, with the potential to reduce power penalty per the device optimization process we described. A main motivation for this on-chip spatial multiplexing is the need to reduce costs. As the laser source serves as the greatest power consumer in an optical system, mode-division multiplexing and other forms of spatial multiplexing can be implemented to push its potentially prohibitive cost metrics down. While the device introduces loss, through imperfect mode isolation, as device fabrication improves, tolerance can increase as well. Meanwhile, the rate that laser power consumption increases as supported wavelengths scales is shown to be much faster than the loss introduced by scaling on-chip bandwidth multi-modally. Future generations of ultra-high capacity devices through spatial multiplexing is explored. Already various systems can be implemented multimodally, with the design features serving as useful for other components. Central to photonic network-on-chips, a multimodal switch fabric, composed of microring resonators, is demonstrated to have error-free operation of 1x2 switching of 10 Gb/s data. These contributions aim to scale bandwidth to ultra-high capacity, while ameliorating any imperfect design, through multiple routes conjoined with on-chip spatial multiplexing, and they constitute the bulk of this dissertation. For the latter part, we turn to the issue of integrating a photonic device for dynamic power reallocation in a system. Specifically, we utilize a 4x4 nonblocking switch fabric composed of Mach-Zehnder interferometers that switch both electro-optically and thermo-optically at ns and μs rates respectively. In order to demonstrate an intelligent platform capable of dynamically multicasting data and reallocating power as needed by the system, we must first initialize the switch fabric to control with an electronic interface. A dithering mechanism, whereby exact cross, bar, and sub-percentage states are enforced through the device, is described here. Such a method could be employed for actuating the device table of bias values to states automatically. We then employ a dynamic power reallocation algorithm through a data acquisition unit, showing real-time channel recovery for channels experiencing power loss by diverting power from paths that could tolerate it. The data that is being multicast through the system is experimentally shown to be error-free at 40 Gb/s data rate, when transmitting from one to three clients and going from automatic bar/cross states to equalized power distribution. For the last portion of this topic, the switch fabric was inserted into a high-performance computing system. In order to run benchmarks at 10 Gb/s data ontop of the switch fabric, a newer model of the control plane was implemented to toggle states according to the command issued by the server. Such a programmable mechanism will prove necessary in future implementations of optical subsystems embedded inside larger systems, like data centers. Beyond the specific control plane demonstrated, the idea of an intelligent photonic layer can be applied to alleviate many kinds of optical channel abnormalities or accommodate for switching based on different patterns in data transmission. Besides spatial-multiplexing, expanding on-chip bandwidth can be accomplished by extension of the wavelength detection regime to a longer regime. Experimental demonstration of photodetection at 1.9 μm is shown with Si+-doped Si photodetectors at 1 Gb/s data operation featuring responsivities of .03 AW−1 at 5 V bias. The same way of processing these Si ribbed waveguide photodetectors can garner even longer wavelength operation at 2.2 μm wavelength. Finally, the experimental demonstration of a coherent perfect absorption Si modulator is exhibited, showing a viable extinction ratio of 24.5 dB. Using this coherent perfect absorption mechanism to demodulate signals, there is the added benefit of differential reception. Currently, an automated process for data collection is employed at a faster time scale than instabilities present in fibers in the setup with future implementations eliminating the off-chip phase modulator for greater signal stability. The field of SiPh has developed to a stage where specific application domains can take off and compete according to industrial-level standards. The work in this dissertation contributes to experimental demonstration of a newly developing area of mode-division multiplexing for substantially increasing bandwidth on-chip. While implementing the discussed photonic devices in dynamic systems, various attributes of integrated photonics are leveraged with existing electronic technologies. Future generations of computing systems should then be designed by implementing both system and device level considerations.

Time resolved imaging is concerned with the measurement of photon arrival time. It has a wealth of emerging applications including biomedical uses such as fluorescence lifetime microscopy and positron emission tomography, as well as laser ranging and imaging in three dimensions. The impact of time resolved imaging on human life is significant: it can be used to identify cancerous cells in-vivo, how well new drugs may perform, or to guide a robot around a factory or hospital. Two essential building blocks of a time resolved imaging system are a photon detector capable of sensing single photons, and fast time resolvers that can measure the time of flight of light to picosecond resolution. In order to address these emerging applications, miniaturised, single-chip, integrated arrays of photon detectors and time resolvers must be developed with state of the art performance and low cost. The goal of this research is therefore the design, layout and verification of arrays of low noise Single Photon Avalanche Diodes (SPADs) together with high resolution Time-Digital Converters (TDCs) using an advanced silicon fabrication process. The research reported in this Thesis was carried out as part of the E.U. funded Megaframe FP6 Project. A 32x32 pixel, one million frames per second, time correlated imaging device has been designed, simulated and fabricated using a 130nm CMOS Imaging process from ST Microelectronics. The imager array has been implemented together with required support cells in order to transmit data off chip at high speed as well as providing a means of device control, test and calibration. The fabricated imaging device successfully demonstrates the research objectives. The Thesis presents details of design, simulation and characterisation results of the elements of the Megaframe device which were the author’s own work. Highlights of the results include the smallest and lowest noise SPAD devices yet published for this class of fabrication process and an imaging array capable of recording single photon arrivals every microsecond, with a minimum time resolution of fifty picoseconds and single bit linearity.

nÃo hà / Tecnologia da InformaÃÃo QuÃntica à uma Ãrea multidisciplinar nova que tem recebido muita atenÃÃo por ser promissora e devido a seu alto potencial em resolver problemas ainda nÃo solucionados. Dentro desta grande Ãrea, as ComunicaÃÃes QuÃnticas estÃo bastante desenvolvidas. Nesta sub-Ãrea, distribuiÃÃo QuÃntica de Chaves à o campo mais avanÃado. Ela permite que duas partes, chamadas Alice e Bob, compartilhem uma chave criptogrÃfica atravÃs de um canal seguro (seguranÃa garantida por leis da mecÃnica quÃntica). A maior parte dos Sistemas de DistribuiÃÃo QuÃntica de Chaves à executada em enlaces de fibras Ãpticas e, nestes sistemas, a mais importante parte à o Detector de FÃtons Isolados. Detector de FÃtons Isolados à um equipamento capaz de absorver um fÃton e gerar um sinal TTL. Assim, em um Detector de FÃtons Isolados ideal, cada fÃton que chega deve disparar um pulso TTL na saÃda. Dado que a energia de um fÃton isolado à muito baixa, um fotodiodo de avalanche à usado para realizar o processo absorÃÃo do fÃtongeraÃÃo de portador, uma vez que este fotodiodo, se corretamente polarizado, pode disparar uma avalanche de portadores detectÃvel. ApÃs a avalanche ter se iniciado, ela deve ser extinta para evitar qualquer dano ao fotodiodo, o que à feito por um circuito de extinÃÃo de avalanche. O fotodiodo de avalanche à o elemento mais importante de um Detector de FÃtons Isolados e sua caracterizaÃÃo requer muita atenÃÃo. Neste contexto, esta dissertaÃÃo lida com aspectos teÃricos e prÃticos de Detectores de FÃtons Isolados para ComunicaÃÃes QuÃnticas. Inicia com a teoria de fotodiodos de avalanche e circuitos de extinÃÃo (resultados numÃricos de circuitos de extinÃÃo tambÃm sÃo mostrados), e segue atà a caracterizaÃÃo de um Detector de FÃtons Isolados construÃdo em laboratÃrio e suas aplicaÃÃes em metrologia de dispositivos Ãpticos, bem como em resoluÃÃo de nÃmero de fÃtons. / Quantum Information Technology is a new multi-disciplinary area which has received a lot of attention due to its promises and its high potential in solving problems still unsolved. In this big area, Quantum Communication is too much developed. In this subarea, Quantum Key Distribution is the most advanced field. It permits two parties, named Alice and Bob, sharing a cryptography key through a secure channel (guaranteed by laws of quantum mechanics). The most of Quantum Key Distribution Systems run over optical fiber links and, in these systems, the most important part is the Single-Photon Detector. Single-Photon Detector is an equipment able to absorb a photon and generate a TTL pulse. Thus, in an ideal Single-Photon Detector, each photon incoming must trigger a TTL pulse at the output. Since the energy level of a single-photon is too much low, an avalanche photodiode is used to perform the photon absorption-carrier generation process, once this photodiode if correctly biased can trigger a detectable avalanche of carriers. After the avalanche has been started, it must be quenched in order to avoid any damage to the photodiode, which is made by an avalanche quenching circuit. The avalanche photodiode is the most important element of a Single-Photon Detector and its characterization requires much attention. In this context, this dissertation deals with theoretical and practical aspects of Single-Photon Detectors for Quantum Communication. It starts from the theory of avalanche photodiodes and quenching circuits (numerical results of quenching circuits are also shown) and follows until the characterization of a home-made Single-Photon Detector and its applications in Metrology of optical devices and in Photon-Number Resolution as well.

<p>The world’s largest particle accelerator, Large Hadron Collider, located at CERN outside Geneva performed its first proton-proton collisions in November 2009. One of the four main experiments is LHCb, studying rare decays of hadrons containing the beauty quark. An essential part of the particle identification in LHCb is made by the two Ring Imaging Cherenkov detectors. These detectors use pixel Hybrid Photon Detectors for detection and imaging of Cherenkov rings. This paper reports on measurements carried out on the Hybrid Photon Detectors, including a discussion of the results. In particular, ageing effect and image stability are studied. A fraction of the photon detectors show a degradation in performance within these fields.</p> / <p>Världens största partikelaccelerator, LHC, belägen vid CERN utanför Genève utförde sina första proton-proton kollisioner i November 2009. Ett av de fyra huvudexperimenten är LHCb, som studerar sällsynta sönderfall av hadroner innehållande <em>b</em> kvarken. En viktig del av partikelidentifikationen i LHCb görs av de två RICH detektorerna. Dessa använder hybrida fotondetektorer för detektering och avbildning av Cherenkov ringar. Denna rapport handlar om mätningar utförda på dessa hybrida fotondetektorer, med en diskussion av resultaten. I synnerhet studeras åldringseffekter och bildstabilitet. En andel av fotondetektorerna visar en degradering i prestanda inom dessa områden.</p>