Kajian Aspek Security Pada Jaringan Informasi Dan Komunikasi Berbasis Visible Light Communication

Cahaya tampak dapat dimanfaatkan sebagai media informasi ataupun komunikasi, teknologi ini dikenal dengan istilah Visible Light Communication yang menawarkan beberapa keunggulan dibandingkan komunikasi nirkabel lainnya seperti RF dan IR. Yakni cakupan bandwidth lebih lebar dan bebas lisensi, aman bagi kesehatan manusia dan tidak terganggu interferensi elektromagnetik. Sistem VLC terdiri atas tiga bagian besar, yakni bagian transmitter dengan menggunakan devais LED, kanal yang berupa ruang bebas (free space) dan receiver dengan menggunakan devais photodetector atau image camera. Penerapan VLC berlandaskan pedoman IEEE 802.15.17 yang mana baru dirancang dalam waktu 5 tahun belakangani ini (sejak tahun 2009), meliputi meliputi layer fisik (physical layer) dan layer MAC (medium access control).  Sebagaimana teknologi komunikasi pada umumnya, VLC juga menyediakan akses security yang dibahas pada bagian layer MAC. Namun pada praktiknya masih belum begitu masif dilakukan oleh para peneliti. Hal ini sangat wajar karena mengingat VLC merupakan teknologi yang sedang dalam tahap pengembangan yang menjadikan penelitian VLC umumnya berfokus pada ‘bagaimana meningkatkan speed dari keterbatasan komponen-komponen pembangun (IC, photodiode, LED, transistor, dll) yang tersedia saat ini\u27. Tantangan teknologi VLC selain target peningkatan kecepatan bit-rate, mobility communication, mengurangi interference noise, menyediakan layanan multi-acces juga salah satunya adalah isu security. Makalah ini merupakan studi literature (review paper) yang didapatkan dari dokumen-dokumen hasil peneltian baik di jurnal dan conference terkait dengan praktik-praktik security VLC yang pernah dilakukan dengan skema indoor maupun outdoor

Analysis, Design and Implementation of an End-to-End QKD Link

This manuscript discusses the most relevant aspects of the practical implementation of a long-range Quantum Key Distribution (QKD) link with trusted nodes, achieving the highest possible secret key rate generation within the security and system level constraints. To this purpose, we report on recent pilot studies for the measurements of detection efficiency and source photon statistics for validating the calibration facilities (i) at telecom wavelength for realistic quantum backbone implementation through standard telecommunications grade optical fiber, and (ii) for the telecom and VIS-NIR regime. In addition, since there are circumstances when a fiber optical link may not be available, we will also discuss the characterization of a Free Space Optics (FSO) QKD link. Finally, the manuscript also discusses the problem of information reconciliation in Continuous Variable QKD (CV-QKD) scenarios

Quantum Communication Systems: Vision, Protocols, Applications, and Challenges

The growth of modern technological sectors have risen to such a spectacular level that the blessings of technology have spread to every corner of the world, even to remote corners. At present, technological development finds its basis in the theoretical foundation of classical physics in every field of scientific research, such as wireless communication, visible light communication, machine learning, and computing. The performance of the conventional communication systems is becoming almost saturated due to the usage of bits. The usage of quantum bits in communication technology has already surpassed the limits of existing technologies and revealed to us a new path in developing technological sectors. Implementation of quantum technology over existing system infrastructure not only provides better performance but also keeps the system secure and reliable. This technology is very promising for future communication systems. This review article describes the fundamentals of quantum communication, vision, design goals, information processing, and protocols. Besides, quantum communication architecture is also proposed here. This research included and explained the prospective applications of quantum technology over existing technological systems, along with the potential challenges of obtaining the goal.Comment: 23 pages, 11 Figure

Next-generation single-photon sources using two-dimensional hexagonal boron nitride

With the second quantum revolution unfolding, the realization of optical quantum technologies will transform future information processing, communication, and sensing. One of the crucial building blocks of quantum information architectures is a single-photon source. Promising candidates for such quantum light sources are quantum dots, trapped ions, color centers in solid-state crystals, and sources based on heralded spontaneous parametric down-conversion. The recent discovery of optically active defects hosted by 2D materials has added yet another class to the solid-state quantum emitters. Stable quantum emitters have been reported in semiconducting transition metal dichalcogenides (TMDs) and in hexagonal boron nitride (hBN). Owing to the large band gap, the energy levels of defects in hBN are well isolated from the band edges. In contrast to TMDs, this allows for operation at room temperature and prevents non-radiative decay, resulting in a high quantum yield. Unlike NV centers in diamond and other solid-state quantum emitters in 3D systems, the 2D crystal lattice of hBN allows for an intrinsically ideal extraction efficiency. In this thesis, advances in developing this new type of emitter are described. In the first experiment, quantum emitters hosted by hBN are attached by van der Waals force to the core of multimode fibers. The system features a free space and fiber-coupled single-photon generation mode. The results can be generalized to waveguides and other on-chip photonic quantum information processing devices, thus providing a path toward integration with photonic networks. Next, the fabrication process, based on a microwave plasma etching technique, is substantially improved, achieving a narrow emission linewidth, high single-photon purity, and a significant reduction of the excited state lifetime. The defect formation probability is influenced by the plasma conditions, while the emitter brightness correlates with the annealing temperature. Due to their low size, weight and power requirements, the quantum emitters in hBN are promising candidates as light sources for long-distance satellite-based quantum communication. The next part of this thesis focuses on the feasibility of using these emitters as a light source for quantum key distribution. The necessary improvement in the photon quality is achieved by coupling an emitter with a microcavity in the Purcell regime. The device is characterized by a strong increase in spectral and single-photon purity and can be used for realistic quantum key distribution, thereby outperforming efficient state-of-the-art decoy state protocols. Moreover, the complete source is integrated on a 1U CubeSat, a picoclass satellite platform encapsulated within a cube of length 10cm. This makes the source among the smallest, fully self-contained, ready-to-operate single-photon sources in the world. The emitters are also space-qualified by exposure to ionizing radiation. After irradiation with gamma-rays, protons and electrons, the quantum emitters show negligible change in photophysics. The space certification study is also extended to other 2D materials, suggesting robust suitability for use of these nanomaterials for space instrumentation. Finally, since the nature of the single-photon emission is still debated and highly controversial, efforts are made to locate the defects with atomic precision. The positions at which the defects form correlate with the fabrication method. This allows one to engineer the emitters to be close to the surface, where high-resolution electron microscopy can be utilized to identify the chemical defect. The results so far prove that quantum emitters in hBN are well suited for quantum information applications and can also be integrated on satellite platforms. A device based around this technology would thus provide an excellent building block for a worldwide quantum internet, where metropolitan fiber networks are connected through satellite relay stations

Semiconductor quantum dots for photonic quantum repeaters

Current information exchange is based on optical fibers and satellite communication via free-space links, where security is provided by mathematical complexity. However, it could potentially be threatened by paradigm shifts in computing technology. Encryption techniques using quantum key distribution based on entangled photons would allow for theoretical full secure communication. The very same platform, entangled photons, can also be employed as a core element to establish multi-node secure communication—a concept known as quantum network. For these reasons, en tangled photon sources might be the core of future quantum networks for secure communication. In this thesis, I study GaAs/AlGaAs quantum dots as entangled photon sources. After giving a general overview on the fundamentals of photonic quantum networks and GaAs droplet-etched quantum dots, I mainly focus on two aspects of the development of this technology. First, limits of the source performance as entangled photon sources and second, applications of entangled photons from quantum dots for secure communication. The prior includes degrading effects of entanglement in these quantum dots, especially based on multiphoton emission and optical Stark effect induced by the particular entangled-photon generation technique, resonant two-photon excitation. The experimental results demonstrate that multiphoton emission is negligible under practical conditions, which is supported by a probabilistic model. The finite excitation laser pulse duration in resonant two-photon excitation, on the other hand, induces an optical Stark effect. The measurements in this thesis support the theoretical predictions and an entanglement reduction by increasing excitation laser pulse length is observed experimentally. If some conditions are met, GaAs/AlGaAs quantum dots emit highly entangled photons, which are utilized in the second part of this thesis by applying them in entanglement-based quantum key distribution protocols. The demonstrations range from the first implementation of quantum dots as entangled photon sources for secure communication in fiber and free-space, to a continuous secret key exchange over three days. The second test case, in particular, tackles the challenges of real-life applications such as sunlight and mild rain. At the end, I provide a brief outlook on how to use entangled photons from GaAs/AlGaAs quantum dots to transfer information from one node of a network, namely a quantum repeater, to another by proposing an experiment called remote quantum teleportation

A Quantum Light Source for Quantum Information Applications in the Telecom C-Band

Semiconductor quantum dot (QD) quantum light sources have long been established as suitable candidates for many quantum information applications, due to the on-demand emission of highly pure and highly indistinguishable single and entangled photons. A key factor in the development of this technology is the operation over the standard telecommunication optical fibre network infrastructure, where the minimum absorption wavelength window is centred on the telecom C-band (1530 – 1565 nm). Initial experiments in this work demonstrated single-photon emission of a QD light source emitting directly in the telecom C-band, under both continuous wave (CW) and 1-GHz pulsed excitation regimes. The QDs were further characterised in terms of fine-structure splitting (FSS) and coherence time, in order to determine their suitability for quantum entanglement and interference-based applications. Long coherence times were observed in the majority of the QDs considered, allowing the demonstration of Hong-Ou-Mandel-type two-photon interference of subsequently emitted photons under CW excitation. The post-selected interference visibility was found to be limited by only the detector resolution and single-photon purity. A further demonstration of high-visibility interference under the same limitations was then made using QD photons and dissimilar photons from a laser, forming the basis of a fibre-based quantum relay. Working further towards a quantum relay, polarisation-entangled photon pairs in the telecom C-band were then generated using the radiative cascade of the biexciton, where a record high fidelity to the ©+ Bell state was observed under both CW and 1-GHz pulsed excitation regimes. While an anomalous effect of the FSS was observed in a majority of the studied QDs, a further characterisation of the FSS in terms of the QD polarisation eigenstates confirmed the emission of entangled photon pairs from such an anomalous-splitting QD. Finally, the work of this thesis was combined to demonstrate a proof-of-principle quantum relay using a QD light source in the telecom C-band. The relay was operated first under CW excitation where polarisation encoded laser input qubits were used and high-fidelity quantum teleportation was observed. In an effort to demonstrate a more technologically relevant application, the quantum relay was subsequently operated at 1 GHz in order to demonstrate the teleportation of initially time-bin encoded laser input qubits. A high mean teleportation fidelity was again observed, demonstrating the potential of this telecom C-band QD quantum light source in the future of long-distance quantum information applications

Design and implementation of a high-speed free-space quantum key distribution system for urban scenarios

Tesis doctoral inédita leída en la Universidad Autónoma de Madrid. Facultad de Ciencias, Departamento de Física de Materiales. Fecha de lectura: 21-06-201