" Active " Teleportation of a Quantum Bit Quantum State Teleportation (qst), Introduced

We report the experimental realization of the ”active” quantum teleportation (QST) of a one-particle entangled qubit. This demonstration completes the original QST protocol and renders it available for actual implementation in quantum computation networks. It is accomplished by implementing a 8m optical delay line and a single-photon triggered fast Electro-Optic Pockels cell. A large value of teleportation ”fidelity” was attained: Fa = (90 ∓ 2)%. Our work follows the line recently suggested by H. W. Lee and J. Kim, Phys. Rev. A 63, 012305 (2000) and E.Knill, R.Laflamme and G.Milburn Nature 409: 46 (2001). PACS: 03.65.Ud, 03.67.Hk, 42.50.Ar, 89.70.+c Quantum state teleportation (QST), introduced by C. H. Bennett, G.Brassard, C. Crepeau, R. Jozsa, A. Peres and W. Wootters came to be recognized in the last decade as a fundamental method of quantum communication and, more generally as one of the basic ideas of the whole field of quantum information [1]. Following the original teleportation paper and its continuous-variables version [2] an intensive experimental effort started for the practical realization of teleportation. Quantum state teleportation (QST) was in facts realized in a number of experiments [3], [4] and [5]. Very recently a ”qubit teleportation” with a unprecedented large ”fidelity” (F ≈ 0.95) has been experimentally demonstrated by our laboratory in the context of quantum optics by adoption of the concept of ”entanglement of one photon with the vacuum” by which each quantum superposition state, i.e. a qubit was physically implemented by a two dimensional subspace of Fock states of a mode of the electromagnetic field, specifically the space spanned by the QED ”vacuum” and the 1-photon state [6]. Precisely, if A and B represent two different modes of the field, with wavevectors (wv) kA and kB directed respectively towards two distant stations (Alice and Bob), these ones may be linked by a non-local channel expressed by an entangled state implying the quantum superposition of a single photon, e.g. by the singlet : |Φ〉singlet = 2 1 2 (|1〉A |0〉B − |0〉A |1〉B). Here the mode indexes 0 and 1 denote respectively the vacuum and 1-photon Fock state population of the modes kA, kB and the superposition state may be simply provided by an optical beam splitter (BS),