The basic ideas in quantum information processing (QIP) dates from several decades back, however the research development based on these ideas started only a little more than a decade ago.The initial ideas of quantum information processing emerged from the fundamental difference between quantum physics and classical physics.It was, and still is, hard to analyse quantum systems in general, and in particular when a quantum system gets bigger, it soon becomes intractable even with high performance computers.To analyse a quantum system, Feynman suggested that we should use a computer based on quantum physics.This is the initial idea of quantum information processing.By contrast to quantum computers, all non-quantum-physicsbased computers, that is, all the existing ones including high performance computers, are now called "classical computers" indicating computers based on classical physics.The research on quantum information processing did not take off until 1990s.Until then, the technology to manipulate quantum was yet not ready, and more importantly, the theory for QIP was not developed enough to show the way to efficiently use quantum nature to carry out computation.Quantum key distribution (QKD) was one of the first QIP protocols successfully implemented and developed in 1990s.QKD is a protocol to exchange secure key material between authenticated users at a distance.Thanks to a property that overlapping quantum states cannot be cloned without trace of interaction, the protocol can detect an eavesdropper by measuring the quantum states and post-processing the signals via classical communication between the users.As one-time pad using QKD was proven to be secure against an eavesdropper who has unbounded ability, unlike conventional cryptogra-
The basic ideas in quantum information processing (QIP) dates from several decades back, however the research development based on these ideas started only a little more than a decade ago.The initial ideas of quantum information processing emerged from the fundamental difference between quantum physics and classical physics.It was, and still is, hard to analyse quantum systems in general, and in particular when a quantum system gets bigger, it soon becomes intractable even with high performance computers.To analyse a quantum system, Feynman suggested that we should use a computer based on quantum physics.This is the initial idea of quantum information processing.By contrast to quantum computers, all non-quantum-physicsbased computers, that is, all the existing ones including high performance computers, are now called "classical computers" indicating computers based on classical physics.The research on quantum information processing did not take off until 1990s.Until then, the technology to manipulate quantum was yet not ready, and more importantly, the theory for QIP was not developed enough to show the way to efficiently use quantum nature to carry out computation.Quantum key distribution (QKD) was one of the first QIP protocols successfully implemented and developed in 1990s.QKD is a protocol to exchange secure key material between authenticated users at a distance.Thanks to a property that overlapping quantum states cannot be cloned without trace of interaction, the protocol can detect an eavesdropper by measuring the quantum states and post-processing the signals via classical communication between the users.As one-time pad using QKD was proven to be secure against an eavesdropper who has unbounded ability, unlike conventional cryptogra-
The theoretical, experimental and technological areas covering the use of quantum mechanics for communication and computation.Quantum information processing includes investigations in quantum information theory, quantum communication, quantum computation, quantum algorithms and their complexity, and quantum control.The science of quantum information processing is a highly interdisciplinary field.In the context of mathematics it is stimulating research in pure mathematics (e.g.coding theory, *algebras, quantum topology) as well as requiring and providing many opportunities for applied mathematics.The science of quantum information processing emerged from the recognition that usable notions of information need to be physically implementable.In the 1960s and 1970s researchers such as R. Landauer, C. Bennett, C. Helstrom and A. Holevo realized that the laws of physics give rise to fundamental constraints on the ability to implement and manipulate information.Landauer repeatedly stated that "information is physical", providing impetus to the idea that it should be possible to found theories of information on the laws of physics.This is in contrast to the introspective approach which led to the basic definitions of computer science and information theory as formulated by A. Church, A. Turing, C. Shannon and others in the first half of the 20th century.Early work in studying the physical foundations of information focused on the effects of energy limitations and the need for dissipating heat in computation and communication.Beginning with S. Wiesner's work on applications of quantum mechanics to cryptography in the late 1960s, it was realized that there may be intrinsic advantages to using quantum physics in information processing.Quantum cryptography and quantum communication in general were soon established as interesting and non-trivial extensions of classical communication based on bits.That quantum mechanics may be used to improve the efficiency of algorithms was first realized when attempts at simulating quantum mechanical systems resulted in exponentially complex algorithms compared to the physical resources associated with the system simulated.In the 1980s, P. Benioff and R. Feynman introduced the idea of a quantum computer for efficiently implementing quantum physics simulations.Models of quantum computers were developed by D. Deutsch, leading to the formulation of artificial problems that could be solved more efficiently by quantum than by classical computers.The advantages of quantum computers became widely recognized when P.
In order to provide novel techniques for processing, storing, and transmitting information, the multidisciplinary field of quantum information science (QIS) integrates ideas from quantum physics [ 4 ] with information science. However, due to a number of events, including Peter Shor’s invention of quantum algorithms and the rise in interest in quantum computing, the history of QIS started to expand quickly in the early to middle 1990s. Peter Shor, a physicist and mathematician, developed the first quantum algorithm that could factor big numbers exponentially more rapidly than any classical algorithm in 1994. This finding triggered strong interest in quantum computing’s potential to tackle issues that are currently unsolvable for classical computers. Since then, QIS has advanced due to the development of novel quantum algorithms and enhancements in the hardware used for quantum computing. Understanding complex quantum phenomena like entanglement and superposition and developing novel strategies for utilizing them for information processing and communication are the core goals of QIS. Quantum bits (qubits) can exist in superpositions of 0 and 1 simultaneously, which enables far more efficient computation than classical bits, which can only be in one state or the other at a given time. Superposition is a key concept in quantum computing. In addition to superposition, entanglement, coherence, and quantum algorithms are other important QIS concepts. Entanglement is a key feature of quantum mechanics and has been observed experimentally in a wide range of physical systems, including photons, atoms, and superconducting qubits. Two particles can get entangled with one another through a phenomenon called entanglement in which their quantum states exhibit a high correlation. This indicates that even if two particles are separated by a considerable distance, modifying the state of one can change the state of the other. No matter how far away two separate particles are from one another when they are entangled, measuring the state of one particle immediately gives the state of another particle. It plays a central role in many quantum technologies, including quantum computing for solving complex problems that take classical computers a long time to solve, quantum cryptography for secure communications, quantum sensing for quantum properties of particles to enable more precise measurements, and quantum networking to improve communication and processing speed over both short and long distances. Quantum metrology methods use the principles of quantum mechanics to improve the accuracy of measurements in fields like gravity sensors, timekeeping, and frequency standards. Some of the benefits of QIS are enhanced computing power, improved communication, advanced cryptography, more precise scientific measurements, and better logistics optimization.
The ideas behind Quantum Information Processing (QIP) began to appear about twenty years ago and theoretical developments have been appearing ever since. Over the last decade quantum experiments have begun to realize QIP and point the way towards the routes for future quantum information technology. This review is a simple introduction to QIP for non-experts. It discusses the basic ideas of and the underpinning quantum theory needed to understand them, as well as various applications and algorithms, and some of the main candidate routes for realizing QIP.
Quantum technology, and especially quantum computing, is advancing rapidly. Our every-day secure communication infrastructure relies heavily on public key cryptography; unfortunately, many public key schemes are in fact insecure against quantum algorithms. Furthermore, adversaries who, today, capture information encrypted using classical key distribution systems, can wait and, as soon as quantum computers of sufficient power become available, they may decipher all previously captured information. While some new “post-quantum” public key systems are assumed to be secure against quantum computers, this is only an assumption and, even if the assumption remains valid, still results in systems that are less efficient for end-users than the more commonly used public key systems employed today. While the advent of quantum technology may seem detrimental to security, in fact, one may harness the power of quantum through quantum key distribution (QKD) for stronger security guarantees. Such QKD protocols allow two (or more) parties to establish a shared secret key, secure against an all-powerful adversary. Perhaps surprising is that QKD technology is already here both experimentally and commercially. This tutorial serves as an introduction to basic QKD along with QKD technology from a practical perspective. Quantum communication is a highly interdisciplinary field of research and one of the goals of this article is to introduce a larger set of researchers and practitioners to its study in the hopes of furthering its progress and eventual wide-scale adoption.
Information security is a growing concern in our modern world, where almost everything can be done online. To protect security, classical encryption protocols, such as RSA, are used. These encryption protocols are almost always based on mathematical problems that are computational difficult. Therefore, the security is only valid under limited computational resources, and therefore do not provide provable security. An exception is the one-time pad protocol, which is provably secure but requires an existing shared key that is as long as the information it must encrypt. The exchange of such a key can be challenging, often requiring the two partied to physically meet to exchange the key or the use a trusted courier to physically carry the key on a hard drive. \n \nQuantum key distribution (QKD) offers a solution by utilizing quantum mechanics to grow a secure cryptographic key shared between two distant parties. The quantum nature of the particles used in the exchange ensure that any eavesdropper would leave signs of their presence, allowing the users to precisely quantify the security of the key that is produced. This allows secure generation of a random key which can be used for the one-time pad encryption protocol which, unlike most encryption protocols, does not rely on computational assumptions, and is secure regardless of available computational power. \n \nCurrent implementations of QKD are limited to a single link distance of ≈200 km, preventing implementation of QKD on a global scale, or even between distant cities within a single country, without some additional techniques. One promising solution is the use of orbiting low Earth orbit satellite platforms as trusted nodes in a quantum communications network. The main purpose of this work has been to show the viability of this solution, trough theoretical performance modeling and experimental demonstrations. \n \nThorough numerical simulations have been developed to evaluate the performance and challenges in implementing QKD using a low Earth orbit satellite platform and determine an optimal approach to its implementation. The simulations include a realistic satellite orbit analysis, all expected loss mechanisms, estimates of background contributions and realistic simulation of quantum optical processes. This work addresses the questions of optimal wavelength and beam waist, the effect of the telescope design and pointing error, and the impact of detector degradation due to exposure to radiation in the space environment. The simulation is used to determine the length of secure key for QKD and the performance of fundamental quantum optics experiments such as Bell tests and quantum teleportation. We compare the advantages and disadvantages of uplink and dowlink scenarios, and show that an uplink, despite having reduced performance compared to a downlink, offers more scientific freedom, by allowing changes to the quantum source, and benefits from a simpler satellite design with reduced pointing requirement. This work provides a theoretical foundation for ongoing design and development of quantum systems for satellite implementation of QKD. \n \nIn addition to theoretical analyses, experiments where developed and conducted corresponding to the challenges likely to be faced by a satellite uplink. Two main challenges where identified and experimentally overcome. First, the difficulty of operating in the high loss regime of a satellite uplink, which typically experience losses in the range of 40-50 dB when above 40° of elevation from the horizon, an elevation only reached by half of the satellite passes. This challenge was addressed by demonstrating full QKD protocols at losses exceeding 50 dB. Also, the ability to perform full QKD during the short duration of a satellite pass was shown by replicating the varying loss of archetypal passes and successfully extracting secure keys. Secondly, the difficulty of accurately tracking and pointing to a receiver platform traveling at the high angular speed of a satellite was overcome by successfully exchange quantum signals to a truck traveling at angular speeds exceeding that of a low Earth orbit satellite. This required the design, construction, and implementation of a transmitter system and a quantum receiver system capable of active pointing using a custom pointing system. \n \nAn additional experiment was also performed where we experimentally investigate the feasibility of performing QKD using light scattered by a diffusive screen. A system capable of doing so could be used to create QKD hot-spots, where a QKD source could be aimed at a diffusive screen to allow multiple users to simultaneously exchange secure keys with the source without the need for high precision pointing. \n \nThrough these analyses and experimental demonstrations we evaluated the performance of QKD using a satellite and have shown its technological readiness to be implemented. Implementation of such a system would allow QKD to be performed on a global scale, enabling communications security that is not based on computational assumptions without the need to physically transport the key from one party to the other.
In nanotechnology, one is dealing with physical systems at a scale so small that quantum effects are important. As the size of computer chips decreases, one eventually reaches the point where quantum effects, wanted or not, occur. If these quantum effects can be controlled, they can be exploited to build computers that can do some tasks more effectively than classical ones. Moreover, quantum particles can be be used advantageously for other purposes in information technology, most notably for communication and cryptography. In fact, experiments demonstrating the feasibility of the process known as quantum key distribution (QKD) are quite impressive. QKD, which is described in Sec. 9.5.1, is likely to be practical long before a full-fledged quantum computer (QC) is built. The area of quantum information theory (QIT) encompasses quantum computation, quantum communication, and quantum cryptography. A device for implementing any of these is called a quantum information processor. We begin by considering methods of encoding information in such devices.