Quantum cryptography, entanglement and teleportation: experiments with photons

The last years have seen a remarkable advance of experimental quantum communication. The most important example is quantum cryptography [1], which promises information-theoretic secure encoding and exchange of confidential messages. After a general introduction into quantum cryptography and the concept of “time-bin” quantum bits, I will present a quantum cryptography scheme based on single photons approximated by faint laser pulses [2]. I will then talk about the distribution of time-bin entanglement [3], and present the teleportation of a qubit [4]. All experiments take advantage of quantum states encoded into photons at telecommunication wavelengths as well as optical fibres, which enabled us to demonstrate these basic protocols over long distances. I will finish with a discussion of a quantum repeater, which promises the extension of the quantum cryptography beyond its current limit of 100 km to arbitrary long distances.