This paper introduces quantum communication concepts to the scientists starting to work in the field of quantum optics and quantum information. Several topics are covered: (1) single and entangled photon sources; (2) quantum key distribution protocols; (3) current and future quantum communication networks; (4) experimental realization of singlephoton sources: state-of-the-art. More details on single photon generation and characterization methods are provided on the examples of the author’s results on room-temperature single-photon sources with definite linear and circular polarizations.
This paper introduces quantum communication concepts to the scientists starting to work in the field of quantum optics and quantum information. Several topics are covered: (1) single and entangled photon sources; (2) quantum key distribution protocols; (3) current and future quantum communication networks; (4) experimental realization of singlephoton sources: state-of-the-art. More details on single photon generation and characterization methods are provided on the examples of the author’s results on room-temperature single-photon sources with definite linear and circular polarizations.
This doctoral dissertation deals with the subject of single-photon technology applications. Particular emphasis was placed on the use of single-photon sources in quantum communication, metrology, and further development of quantum computers. At the beginning of this thesis, the development history of cryptography is described, starting from steganography and ending with quantum key distribution protocols. Later, the key elements of the quantum network, such as end nodes and transmission channels, are presented. Various types of sources and single-photon detectors are discussed. Methods for amplifying the signal and correcting errors that occur during transmission are also mentioned. In the further part of this thesis, two examples of single-photon sources are described, along with their experimental implementation. These sources are based on the nonlinear spontaneous parametric down-conversion (SPDC) process, which has also been described in detail. Parameters that specify the quality of a single-photon source (such as conversion efficiency, phase-matching conditions, singleness and photonic density matrix) are also characterized, both mathematically and experimentally. Furthermore, this doctoral dissertation consists of definitions and elaborated descriptions of quantum optical phenomena, which should be useful for those who are not yet familiar with the subject of single-photon sources and their applications or just start their work in this field.
After the preceding four introductory chapters, we are finally ready to discuss optical quantum information processing. While in principle quantum communication can be implemented with atoms or electrons, in practice the implementation of choice for long-distance quantum communication will almost certainly be optical. In this chapter, we will develop some of the key topics in quantum communication with single photons, and we will discuss continuous-variable quantum communication in Chapter 8. In some ways, quantum communication is the most technologically advanced part of quantum information processing. Most protocols in this chapter, such as teleportation and cryptography, have been convincingly demonstrated in the lab, and there are already several commercial organizations that sell cryptographic systems based on quantum mechanical principles. In particular, the promise of secure communication with quantum cryptography is one of the driving forces behind the development of single-photon sources and detectors. In this chapter, we first construct several optical representations of the qubit, including polarized photons and time-bin encoding. Since the single-photon implementation of a qubit is central to optical quantum information processing, this constitutes a large part of the chapter. In Section 5.2 we discuss quantum teleportation and entanglement swapping with single photons. We also present a method for entanglement distillation using entanglement swapping. In Section 5.3 we introduce decoherence-free subspaces, which can be used to reduce noise in the transmission of quantum information, and even establish communication channels in the absence of shared reference frames.
For any communication, the conveyed information must be carried by some physical system. If this system is a quantum system rather than a classical one, its behavior will be governed by the laws of quantum mechanics. Hence, the properties of quantum mechanics, such as superpositions and entanglement, are accessible, opening up new possibilities for transferring information. The exploration of these possibilities constitutes the field of quantum communication. The key ingredient in quantum communication is the qubit, a bit that can be in any superposition of 0 and 1, and that is carried by a quantum state. One possible physical realization of these quantum states is to use single photons. Hence, to explore the possibilities of optical quantum communication, photonic quantum states must be generated, transmitted, characterized, and detected with high precision. This thesis begins with the first of these steps: the implementation of single-photon sources generating photonic qubits. The sources are based on photon-pair generation in nonlinear crystals, and designed to be compatible with fiber optical communication systems. To ensure such a compatibility and to create a high-quality source, a theoretical analysis is made, optimizing the coupling of the photons into optical fibers. Based on the theoretical analysis, a heralded single-photon source and a two-crystal source of entangled photons-pairs are experimentally implemented. The source of entangled photons is further developed into a compact source with a narrow bandwidth compatible with standard telecommunication wavelength-division multiplexers, and even further developed to a more stable one-crystal source. The sources are to be used for quantum communication in general and quantum cryptography in particular. Specifically, a heralded single-photon source is implemented and then used for a full test of a decoy-state quantum cryptography protocol.
Abstract Worldwide, enormous efforts are directed toward the development of the so‐called quantum internet. Turning this long‐sought‐after dream into reality is a great challenge that will require breakthroughs in quantum communication and computing. To establish a global, quantum‐secured communication infrastructure, photonic quantum technologies will doubtlessly play a major role, by providing and interfacing essential quantum resources, for example, flying‐ and stationary qubits or quantum memories. Over the last decade, significant progress has been made in the engineering of on‐demand quantum light sources based on semiconductor quantum dots, which enable the generation of close‐to‐ideal single‐ and entangled‐photon states, useful for applications in quantum information processing. This review focuses on implementations of, and building blocks for, quantum communication using quantum‐light sources based on epitaxial semiconductor quantum dots. After reviewing the main notions of quantum communication and introducing the devices used for single‐photon and entangled‐photon generation, an overview of experimental implementations of quantum key distribution protocols using quantum dot based quantum light sources is provided. Furthermore, recent progress toward quantum‐secured communication networks as well as building blocks thereof is summarized. The article closes with an outlook, discussing future perspectives in the field and identifying the main challenges to be solved.
Optical quantum systems are ideal for testing quantum mechanical laws, but they also find many uses into possible applications to our everyday life related to quantum information science, such as quantum key distribution (QKD) or, in general, quantum communication. Nonlinear and quantum optics and their applications both to quantum communication and to tests of fundamental physics are described in this Thesis. In particular, we have developed and characterised heralded single photon sources at telecommunication wavelengths (1550 nm), based on nonlinear interactions of the second order between electric fields in dielectric materials. This is the starting point for the preparation of single photon entangled states, that we used as a resource for heralded amplification of photonic qubits, with a direct application in Device Independent Quantum Key Distribution (DIQKD) protocols, but also for testing fundamental questions in quantum physics, demonstrating the presence of entanglement in a state that counts a macroscopic number of particles, 500 photons.
Introduction: The analysis of the main directions of research in the field of creating sources of single photons for communication systems with quantum key distribution is carried out. Scientometric analysis based on Scopus database is used to identify the most promising areas and predict the trends in the field of single photon sources. Methods of single photon sources development and their applications in commercial communication systems with quantum key distribution is shown. At the time single photons sources based on quantum dots are the most developed and presented on the market. However, color centers in nanocrystals and carbon nanotubes are intensively studied. The prospects of creating compact and easy-to-use sources of single photons on telecommunication wavelengths is analyzed. There are many ways of realization of single photon sources design. Significant funding in China and Germany leads to notable growth of the technology. It was detected the main journals, author groups and organizations working in direction of single photon sources. Methods and Results: The research field of communication systems using sources of single photons is growing. It is available single photon sources on quantum dots and crystals. Applying of carbon nanotubes is promising for this problem according to some famous authors. It is revealed significant overlap of the research areas: single photon sources, quantum random number generators and quantum key distribution. At the time fundamental studies are implemented in technical devices with high potential for commercial applications.