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arXiv:0705.1748 · Chinese Physics Letters

Efficient Quantum Cryptography Network without Entanglement and Quantum Memory

Chunyan Li, Xihan Li, Deng Fu-Guo, Ping Zhou, Yu-Jie Liang, Hong-Yu Zhou

Published Oct 26, 2006• 167 citations
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Abstract

An efficient quantum cryptography network protocol is proposed with d -dimensional polarized photons, without resorting to entanglement and quantum memory. A server on the network, say Alice, provides the service for preparing and measuring single photons whose initial state are |0⟩. The users code the information on the single photons with some unitary operations. To prevent the untrustworthy server Alice from eavesdropping the quantum lines, a nonorthogonal-coding technique is used in the process that the quantum signal is transmitted between the users. This protocol does not require the servers and the users to store the quantum states and almost all of the single photons can be used for carrying the information, which makes it more convenient for application than others with present technology. We also discuss the case with a faint laser pulse.

DOI
10.1088/0256-307x/23/11/004

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An efficient quantum cryptography network protocol is proposed with d -dimensional polarized photons, without resorting to entanglement and quantum memory. A server on the network, say Alice, provides the service for preparing and measuring single photons whose initial state are |0⟩. The users code the information on the single photons with some unitary operations. To prevent the untrustworthy server Alice from eavesdropping the quantum lines, a nonorthogonal-coding technique is used in the process that the quantum signal is transmitted between the users. This protocol does not require the servers and the users to store the quantum states and almost all of the single photons can be used for carrying the information, which makes it more convenient for application than others with present technology. We also discuss the case with a faint laser pulse.
A quantum secure direct communication network scheme is proposed with quantum superdense coding and decoy photons. The servers on a passive optical network prepare and measure the quantum signal, i.e. a sequence of the d -dimensional Bell states. After confirming the security of the photons received from the receiver, the sender codes his secret message on them directly. For preventing a dishonest server from eavesdropping, some decoy photons prepared by measuring one photon in the Bell states are used to replace some original photons. One of the users on the network can communicate to any other one. This scheme has the advantage of high capacity, and it is more convenient than others as only a sequence of photons is transmitted in quantum line.
The exploit of quantum systems allows for insights that promise to revolutionise information processing, although a main challenge for practical implementations is technological complexity. Due to its feasibility, quantum cryptography, which allows for perfectly secure communication, has become the most prominent application of quantum technology. Nevertheless, this task still requires the users to be capable of performing quantum operations, such as state preparation or measurements in multiple bases. A natural question is whether the users' technological requirements can be further reduced. Here we demonstrate a novel quantum cryptography scheme, where users are fully classical. In our protocol, the quantum operations are performed by an untrusted third party acting as a server, which gives the users access to a superimposed single photon, and the key exchange is achieved via interaction-free measurements on the shared state. Our approach opens up new interesting possibilities for quantum cryptography networks.
We propose a theoretical scheme for secure quantum key distribution network following the ideas in quantum dense coding. In this scheme, the server of the network provides the service for preparing and measuring the Bell states, and the users encode the states with local unitary operations. For preventing the server from eavesdropping, we design a decoy when the particle is transmitted between the users. The scheme has high capacity as one particle carries two bits of information and its efficiency for qubits approaches 100%. Moreover, it is unnecessary for the users to store the quantum states, which makes this scheme more convenient in applications than others.
An efficient quantum secure direct communication network protocol with the two-step scheme is proposed by using the Einstein–Podolsky–Rosen (EPR) pair block as the quantum information carrier. The server, say Alice, prepares and measures the EPR pairs in the quantum communication and the users perform the four local unitary operations to encode their message. Anyone of the legitimate users can communicate another one on the network securely. Since almost all of the instances in this scheme are useful and each EPR pair can carry two bits of information, the efficiency for qubits and the source capacity both approach the maximal values.
Two deterministic secure quantum communication schemes are proposed, one based on pure entangled states and the other on ddd-dimensional single-photon states. In these two schemes, only single-photon measurements are required for the two authorized users, which makes the schemes more convenient than others in practical applications. Although each qubit can be read out after a transmission of additional classical bit, it is unnecessary for the users to transmit qubits double the distance between the sender and the receiver, which will increase their bit rate and their security. The parties use decoy photons to check eavesdropping efficiently. The obvious advantage in the first scheme is that the pure entangled source is feasible with present techniques.
Two quantum secure direct communication schemes are proposed based on pure entangled states and ddd-dimensional single-photon states, respectively. In these two schemes, only single-photon measurements are required for the two authorized users and two practical quantum signal sources are used for carrying information, which makes the schemes more convenient than others in a practical application. Although each qubit can be read out after a transmission of additional classical information, it is unnecessary for the users to transmit qubits carrying the secret message, which will increase their bit rate and their security. The parties use decoy photons to check eavesdropping efficiently.