Broadband teleportation - art. no. 022309

Quantum teleportation of an unknown broadband electromagnetic field is inve stigated. The continuous-variable teleportation protocol by Braunstein and Kimble [Phys. Rev. Leu. 80, 869 (1998)] for teleporting the quantum state o f a single mode of the electromagnetic held is generalized for the case of a multimode field with finite bandwith. We discuss criteria for continuous- variable teleportation with various sets of input states and apply them to the teleportation of broadband fields. We first consider as a set of input fields (from which an independent state preparer draws the inputs to be tel eported) arbitrary pure Gaussian states with unknown coherent amplitude (sq ueezed or coherent states). This set of input states, further restricted to an alphabet of coherent states, was used in the experiment by Furusawa et al. [Science 282, 706 (1998)]. It requires unit-gain teleportation for opti mizing the teleportation fidelity. In our broadband scheme, the excess nois e added through unit-gain teleportation due to the finite degree of the squ eezed-state entanglement is just twice the (entanglement) source's squeezin g spectrum for its "quiet quadrature." The teleportation of one half of an entangled state (two-mode squeezed vacuum state), i.e., "entanglement swapp ing," and its verification are optimized under a certain nonunit gain condi tion. We will also give a broadband description of this continuous-variable entanglement swapping based on the single-mode scheme by van Loock and Bra unstein [Phys. Rev. A 61., to 302 (2000)].