Mohamed Bourennane

Security of quantum key distribution using d-level systems.

We consider two quantum cryptographic schemes relying on encoding the key into qudits, i.e., quantum states in a d-dimensional Hilbert space. The first cryptosystem uses two mutually unbiased bases (thereby extending the BB84 scheme), while the second exploits all d+1 available such bases (extending the six-state protocol for qubits). We derive the information gained by a potential eavesdropper applying a cloning-based individual attack, along with an upper bound on the error rate that ensures unconditional security against coherent attacks.

Quantum Key Distribution Using Multilevel Encoding

We extend the original Bennett and Brassard for quantum key distribution protocol by using M mutually complementary bases and N orthogonalvectors in each base.

Experiments on long wavelength (1550 nm) "plug and play" quantum cryptography systems.

An interferometric quantum cryptographic system at 1550nm wavelength using gated InGaAs Avalanche Photo Diodes as single-photon receivers is demonstrated for a transmission distance up to 40 km.

Experimental long wavelength quantum cryptography: from single-photon transmission to key extraction protocols

Abstract We present experiments on long wavelength (δ = 1.55 μm) ‘plug and play’ quantum cryptography systems. We discuss the performance of single-photon detectors at δ = 1.55 μm. Furthermore, we address the full implementation of the quantum cryptography protocol, discussing in detail the implementation of protocols for error correction and privacy amplification needed to get a secure key. We illustrate the theory with examples from a full software simulation to show the performance of the complete protocol in terms of final secure key creation rate.

Experiments on long wavelength (1550 nm) "plug and play" quantum cryptography systems

An interferometric quantum cryptographic system at 1550nm wavelength using gated InGaAs Avalanche Photo Diodes as single-photon receivers is demonstrated for a transmission distance up to 40 km.

Single-photon counters in the telecom wavelength region of 1550 nm for quantum information processing

Abstract We describe the status of commercially available InGaAs InP avalanche photodiodes for use as single-photon counters in the telecom wavelength region of 1550 nm.

Entanglement-assisted local transformations between inequivalent classes of three-particle entangled states

We show that bipartite and tripartite entangled states cannot be used as catalysis states to enable local transformations inbetween inequivalent classes of three-particle entangled states which are non-interchangeable under local transformations. We find the optimal protocol for conversion of a certain family of the W-states and an EPR-pair into the GHZ-state.

An expectation value expansion of Hermitian operators in a discrete Hilbert space

We discuss a real-valued expansion of any Hermitian operator defined in a Hilbert space of finite dimension N, where N is a prime number, or an integer power of a prime. The expansion has a direct interpretation in terms of the operator expectation values for a set of complementary bases. The expansion can be said to be the complement of the discrete Wigner function. We expect the expansion to be of use in quantum information applications since qubits typically are represented by a discrete, and finite-dimensional, physical system of dimension N = 2p, where p is the number of qubits involved. As a particular example we use the expansion to prove that an intermediate measurement basis (a Breidbart basis) cannot be found if the Hilbert space dimension is three or four.

Quantum communication and single-photon technologies

We discuss single-photon counting technologies, in particular at the optical wavelength of 1550 nm and their application in quantum communication. In particular we discuss the case of quantum cryptography illustrating with experiments performed in our lab, supplemented by recent experiments by other groups. We furthermore discuss briefly more general protocols for quantum communication and address some experimental changes.

Investigations on Long Wavelength Quantum Cryptography Systems

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