A new practical free space quantum communication system is proposed, it is based on the principle of quantum secure direct communication. Quantum cryptography is a practical method to realize free space optical communication. Different from the existing free space quantum key distribution communication system, the free space quantum secure direct communication is deterministic and the system is more simple. In this paper, a new structure of four transmitting channels is prensented, this structure could increase the security and capacity of system. The setup of transmitter and receiver of each transmitting channel is discussed in detail, and the communication process is analyzed. The result shows that this free space quantum system could be realized and can work over long distance.
A new practical free space quantum communication system is proposed, it is based on the principle of quantum secure direct communication. Quantum cryptography is a practical method to realize free space optical communication. Different from the existing free space quantum key distribution communication system, the free space quantum secure direct communication is deterministic and the system is more simple. In this paper, a new structure of four transmitting channels is prensented, this structure could increase the security and capacity of system. The setup of transmitter and receiver of each transmitting channel is discussed in detail, and the communication process is analyzed. The result shows that this free space quantum system could be realized and can work over long distance.
Quantum secure direct communication (QSDC) leverages quantum states to transmit information securely and reliably over a noisy, lossy, and wiretapped quantum channel. It has been proven to be information-theoretically secure. Recent experiments show that QSDC can enable long-distance communication and large-scale networking with existing technologies. In particular, free-space QSDC has the unique advantages and prospects for practical large-scale application. Here, we review the QSDC basics and the progress of free-space QSDC. The feasibility of satellite-based QSDC and the future directions of free-space QSDC are discussed. We propose a practical and feasible route that can make immediate application of QSDC in real life.
Quantum key distribution (QKD) is considered as an ideal method to make secret message unreadable to eaves-dropper but intelligible to the two authorized parties of the communication [1][2][3][4][5][6].In the research of experimental quantum key distribution, single photons and entangled photon pairs are used as the carriers.In quantum key distribution, secret keys are generated first between the communication parties.The security of quantum key distribution is guaranteed by the laws of quantum mechanics.After the quantum key distribution is completed, the communication parties should share secret keys, then the sender encrypts the secret message using the secret keys to form the ciphertext and transmits the ciphertext through a classical channel.The receiver receives the ciphertext and then decrypt the ciphertext to get the secret message.Altogether there are four steps in a secret communication process with QKD: key generation, encryption, transmission and decryption.Here in this review, we review some new development in quantum communication, quantum direct communication (QDC).Quantum direct communication is a form of quantum communication where secret messages can be transmitted through a quantum channel with or without additional classical communications.There are two forms of quantum direct communication, quantum secure direct communication (QSDC) [7{9] and deterministic secure quantum communication (DSQC) [10,11].In QSDC, secret messages are transmitted directly between the communication parties, from sender Alice to receiver Bob, without additional classical communication except those for the necessary eavesdropping check.In other words, the quantum key distribution process and the classical communication of ciphertext are condensed into one single quantum communication procedure in QSDC.Deterministic secure quantum communication is another type of quantum direct communication, such as those proposed in Ref. [10,11], where classical communication is required in order to read out the secret message.As mentioned earlier, to complete a secure communication with the help of QKD, one usually encodes the secret message with an encryption scheme, and the ciphered text is transmitted through a classical channel.With a quantum channel, this procedure can be varied.
In this paper, a new method of safe, secure and efficient way of communication, Quantum Wireless Communication(QWC) is proposed, the security offered by a QWC channel and the different ways of communicating in QWC are also discussed. In terms of complexity, wireless medium has a lot of advantages than that of optical fibers since there are no birefringence effects in the free space. In addition, it also has the advantage of the Wireless Quantum Key Distribution(WQKD) using which a key is exchanged wirelessly from one state to another. Based on these, we will design and achieve a high directional, high bandwidth communication channel with utmost security.
The cryptographic communication has a lot of important applications, particularly in the magnificent prospects of private communication. As one knows, the security of cryptographic channel depends crucially on the secrecy of the key. The Vernam cipher is the only cipher system which has guaranteed security. In that system the key must be as long as the message and most be used only once. Quantum cryptography is a method whereby key secrecy can be guaranteed by a physical law. So it is impossible, even in principle, to eavesdrop on such channels. Quantum cryptography has been developed in recent years. Up to now, many schemes of quantum cryptography have been proposed. Now one of the main problems in this field is how to increase transmission distance. In order to use quantum nature of light, up to now proposed schemes all use very dim light pulses. The average photon number is about 0.1. Because of the loss of the optical fiber, it is difficult for the quantum cryptography based on one photon level or on dim light to realize quantum key-distribution over long distance. A quantum key distribution based on coherent state is introduced in this paper. Here we discuss the feasibility and security of this scheme.
Quantum communication exploits the principles of quantum mechanics in the transmision and processing of information. It has the advantages of high security and high capacity. Quantum secure direct communication (QSDC) is a new mode of quantum coomunication by Long and Liu in which secret information can be transmitted securely and directly over quantum channels. Since it was first proposed in 2000, QSDC has been developed very fast. In this review, we will explain the basic principles of QSDC and describe some typical QSDC protocols. Toward the end of the review, we will introduce the new trends in the QSDC research and give a perspectiv of QSDC research.
When light is propagated through a channel that is not a waveguide, such as a fiber, it is known as a free-space optical channel. When used in communication systems, free-space optical channels provide the advantages of high communication rates, lower power, and minimal infrastructure installation. When the free-space optical channel has a random medium in it, such as the atmosphere, the distortions will be applied to the phase. The phase distortions can lead to intensity fluctuations and additional beam spreading. To compensate for the distortions adaptive optics can be used, allowing for the stability of the system to be improved. Additionally, post processing techniques on transmitted data can also be used to improve the stability of the channel. By significantly decreasing the number of photons transmitted, a classical communication channel can be considered as a quantum channel. Encoding information into the quantum states of the transmitted photons, quantum communication can be performed. When transmitting on the order of 1 photon per pulse, classical post processing techniques cannot be used to improve the stability of the channel. To stabilize the free-space optical channel, adaptive optics can be used at the transmitter or receiver. As no measurement of the quantum state is performed by the adaptive optics system, no information in the photon is lost. In this work, quantum key distribution will be implemented over the quantum channel. The focus of this work is on the design and study of how the channel degradations can be overcome, as well as the establishment of a free-space optical channel with adaptive optics in a quantum networking testbed. Quantum key distribution systems were simulated over a 30 km maritime channel as well as over a underwater channel. For the 30 km channel, the use of multiple parallel spatial modes results in the highest increases of the secure key rate at the cost of transmitting a lower average number of photons. When adaptive optics is applied, the secure key rates have a small increase, however as the strength of the turbulence increases from weak to moderate, the relative improvement is higher. For the underwater channel, operation at lower depths is optimal as fewer background photons reach the receiver and the channel attenuation is lower. In the experimental setup, it was found that the single photon detectors that are being used are the limiting the channel loss to be at most 6 dB. The free space optical link established between the Electrical and Computer Engineering building and College of Optical Sciences uses a corner cube retro-reflector to yield a distance of 1.45 km. The channel has been characterized at various times of day to determine the strength of the atmospheric turbulence, which ranges from a scintillation index of 0.07 to 2.21. A classical communication experiment was performed, resulting in error-free transmission while the input power to the EDFA before the photodetector was consistently above -25 dBm.