Quantum Key Distribution by Utilizing Four-Level Particles

We present a quantum key distribution protocol based on four-level particles entanglement. Furthermore, a controlled quantum key distribution protocol is proposed by utilizing three four-level particles. We show that the two protocols are secure.Comment: 5 pages, no figur

Multiple teleportation via the partially entangled states

We investigate the multiple teleportation with some nonmaximally entangled channels. The efficiencies of two multiple teleportation protocols, the separate multiple teleportation protocol (SMTP) and the global multiple teleportation protocol (GMTP), are calculated. We show that GMTP is more efficient than SMTP.Comment: 4 pages, 2 figure

Entangler and analyzer for multiphoton maximally entangled states using weak nonlinearities

In the regime of weak nonlinearity we present two general feasible schemes. One is an entangler for generating any one of the $n$-photon Greenberger-Horne-Zeilinge (GHZ) states and Bell states. After the interactions with cross-Kerr nonlinear media, a phase gate followed by a measurement on the probe beam, and appropriate local operations via classical feed-forward, one can obtain the desired states in a nearly deterministic way. Another scheme is an analyzer for multiphoton maximally entangled states, which is taken as a further application of the above entangler. In this scheme, all of the $2^n$ $n$-photon GHZ states can, nearly deterministically, be discriminated. Furthermore, an efficient two-step nondestructive Bell-state analyzer is designed.Comment: 7 pages, 6 figure

Generation of four-photon polarization entangled state based on EPR entanglers

We show how to prepare four-photon polarization entangled states based on some Einstein-Podolsky-Rosen (EPR) entanglers. An EPR entangler consists of two single photons, linear optics elements, quantum non-demolition measurement using a weak cross-Kerr nonlinearity, and classical feed forward. This entangler which acts as the most primary part in the construction of our scheme allows us to make two separable polarization qubits entangled near deterministically. Therefore, the efficiency of the present device completely depends on that of EPR entanglers, and it has a high success probability.Comment: 5 pages, 3 figure