In this chapter, I will show that information-transmission (IT) can be carried out within a quantum unit, as defined by the Heisenberg Uncertainty Principle, in which this unit can be translated as a quantum limited subspace (QLS). We will show that the size of a QLS is determined by the carrier bandwidth; that is, the narrower the bandwidth, the larger the size of the QLS can be used for complex amplitude communication. By understanding the pros and the cons of IT within the QLS, more innovative communication techniques can be developed and employed in practice, for example, as applied to security IT within the QLS. Imaging using phase conjugation idea will be illustrated. A new era of innovative communication is anticipated to emerge and it will change the way we used to communicate forever!
In this chapter, I will show that information-transmission (IT) can be carried out within a quantum unit, as defined by the Heisenberg Uncertainty Principle, in which this unit can be translated as a quantum limited subspace (QLS). We will show that the size of a QLS is determined by the carrier bandwidth; that is, the narrower the bandwidth, the larger the size of the QLS can be used for complex amplitude communication. By understanding the pros and the cons of IT within the QLS, more innovative communication techniques can be developed and employed in practice, for example, as applied to security IT within the QLS. Imaging using phase conjugation idea will be illustrated. A new era of innovative communication is anticipated to emerge and it will change the way we used to communicate forever!
One important aspect of our universe is that one cannot get something from nothing; there is always a price to pay. In this article we show that every bit of information is limited by a quantum unit. Since we are communicating within a temporal subspace, this unit can be equivalently described as a quantum limited subspace (QLS), as imposed by the Heisenberg Principle. We show that communication can be exploited within and outside the QLS. The size of a QLS is determined by carrier signal bandwidth; that is narrower the bandwidth the larger the size of the QLS. By manipulating the size of a QLS, more efficient information transmission strategies can be developed. Examples for inside and outside QLS communication are given. Extension to relativistic communication has also demonstrated. We remark that, a new era of communication is anticipated to immerge and it will change our way in communicating, observation and computing, we used to use, forever!
Abstract One important aspect of our universe is that one cannot get something from nothing; there is always a price to pay. In this article we show that every bit of information is limited by a quantum unit. Since we are communicating within a temporal subspace, this unit can be equivalently described as a quantum limited subspace (QLS), as imposed by the Heisenberg Principle. We show that communication can be exploited within and outside the QLS. The size of a QLS is determined by carrier signal bandwidth; that is narrower the bandwidth the larger the size of the QLS. By manipulating the size of a QLS, more efficient information transmission strategies can be developed. Examples for inside and outside QLS communication are given. Extension to relativistic communication has also demonstrated. We remark that, a new era of communication is anticipated to immerge and it will change our way in communicating, observation and computing, we used to use, forever!
In the history of cryptography, quantum cryptography is a new and important chapter. It is a recent technique that can be used to ensure the confidentiality of information transmitted between two parties, usually called Alice and Bob, by exploiting the counterintuitive behavior of elementary particles such as photons. The physics of elementary particles is governed by the laws of quantum mechanics, which were discovered in the early twentieth century by talented physicists. Quantum mechanics fundamentally change the way we must see our world. At atomic scales, elementary particles do not have a precise location or speed, as we would intuitively expect. An observer who would want to get information on the particle's location would destroy information on its speed – and vice versa – as captured by the famous Heisenberg uncertainty principle . This is not a limitation due to the observer's technology but rather a fundamental limitation that no one can ever overcome. The uncertainty principle has long been considered as an inconvenient limitation, until recently, when positive applications were found. In the meantime, the mid-twentieth century was marked by the creation of a new discipline called information theory . Information theory is aimed at defining the concept of information and mathematically describing tasks such as communication, coding and encryption. Pioneered by famous scientists like Turing and von Neumann and formally laid down by Shannon, it answers two fundamental questions: what is the fundamental limit of data compression, and what is the highest possible transmission rate over a communication channel?
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.
“All information is physical”, the slogan advocated over many years by Rolf Landauer of IBM, has recently led to some remarkable changes in the way we view communications, computing and cryptography. By employing quantum physics, several objectives that were thought impossible in a classical world have now proven to be possible. Quantum communications links, for example, become impossible to eavesdrop without detection. Quantum computers (were they to be realized) could turn some algorithms that are labelled “difficult” for a classical machine, no matter how powerful, into ones that become “simple”. The details of what constitutes “difficult” and what “easy” are the subject of mathematical complexity theory, but an example here will illustrate the point and the impact that quantum information processors will have on all of us. The security of many forms of encryption is predicated on the difficulty of factoring large numbers. Finding the factors of a 1024-digit number would take longer than the age of the universe on a computer designed according to the laws of classical physics, and yet can be done in the blink of an eye on a quantum computer were it to have a comparable clock speed. But only if we can build one, and that's the challenge! No one has yet realized a quantum register of the necessary size, or quantum gates with the prerequisite accuracy. Yet it is worth the chase, as a quantum computer with a modest-sized register could out-perform any classical machine.
This article helps us to understand the world with quantum secure communication. In this quantum landscape, the classical barriers of secure communication are transcended, and a brand-new era of impenetrable information safety emerges. The laws of quantum mechanics will be helpful in quantum secure communication for data transmission. It highlights the inherent security blessings conferred by using quantum properties, including the no-cloning theorem and the uncertainty precept, rendering eavesdropping impossible. In addition, this article gives us an understanding of how encryption can be done using quantum computing techniques compared to the classical ones. This article also outlines the challenges and ongoing research within quantum secure communication, addressing problems like sensible implementation, community scalability, and quantum key management. It underscores the collaborative efforts of researchers, industries, and governments in advancing quantum cryptography.