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Several schemes have been proposed to extend Quantum Key Distribution protocols aiming at improving their security or at providing new physical substrates for qubit implementation. We present a toolbox to jointly create, manipulate and measure qubits stored in polarization and transverse-modes degrees of freedom of single photons. The toolbox includes local operations on single qubits, controlled operations between the two qubits and projective measurements over a wide variety of non-local bases in the four dimensional space of states. We describe how to implement the toolbox to perform an extended version of the BB84 protocol for this Hilbert space (ideally transmitting two key bits per photon). We present the experimental implementation of the measurement scheme both in the regimes of intense light beams and with single photons. Thus, we show the feasibility of implementing the protocol providing an interesting example of a new method for quantum information processing using the polarization and transverse modes of light as qubits.
State-of-the-art quantum key distribution systems are based on the BB84 protocol and single photons generated by lasers. These implementations suffer from range limitations and security loopholes, which require expensive adaptation. The use of polari
Quantum key distribution (QKD) promises information-theoretically secure communication, and is already on the verge of commercialization. Thus far, different QKD protocols have been proposed theoretically and implemented experimentally [1, 2]. The ne
We present a setup for quantum cryptography based on photon pairs in energy-time Bell states and show its feasability in a laboratory experiment. Our scheme combines the advantages of using photon pairs instead of faint laser pulses and the possibili
This is a chapter on quantum cryptography for the book A Multidisciplinary Introduction to Information Security to be published by CRC Press in 2011/2012. The chapter aims to introduce the topic to undergraduate-level and continuing-education student
Quantum cryptography is a new method for secret communications offering the ultimate security assurance of the inviolability of a Law of Nature. In this paper we shall describe the theory of quantum cryptography, its potential relevance and the devel