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Security in sensor networks, though an important issue for widely available wireless networks, has been studied less extensively than other properties of these networks, such as, for example, their reliability. The few security schemes proposed so far are based on classical cryptography. In contrast, the present paper develops a new security solution, based on quantum cryptography. The scheme developed here comes with the advantages quantum cryptography has over classical cryptography, namely, effectively unbreakable keys and therefore effectively unconditionally secure messages. Our security system ensures privacy of the measured data field in the presence of an intruder who listens to messages broadcast in the field. [ABSTRACT FROM AUTHOR]

Rank-varying computational complexity describes those computations in which the complexity of executing each step is not a constant, but evolves throughout the computation as a function of the order of execution of each step [2]. This paper identifies practical instances of this computational paradigm in the procedures for computing the quantum Fourier transform and its inverse. It is shown herein that under the constraints imposed by quantum decoherence, only a parallel approach can guarantee a reliable solution or, alternatively, improve scalability. [ABSTRACT FROM AUTHOR]

We develop an entanglement verification method not based on Bell inequalities, that achieves a higher reliability per number of qubits tested than existing procedures of this kind. Used in a quantum cryptographic context, the method gives rise to a new protocol for distributing classical keys through insecure quantum channels. The cost of quantum and classical communication is significantly reduced in the new protocol, while its security is increased with respect to other entanglement-based protocols exchanging the same number of qubits. To achieve this performance, our scheme relies on a simple quantum circuit and the ability to store qubits. [ABSTRACT FROM AUTHOR]

The paper is intended to be a survey of all the important aspects and results that have shaped the field of quantum computation and quantum information. The reader is first familiarized with those features and principles of quantum mechanics providing a more efficient and secure information processing. Their applications to the general theory of information, cryptography, algorithms, computational complexity and error-correction are then discussed. Prospects for building a practical quantum computer are also analyzed. [ABSTRACT FROM AUTHOR]