On the Capacity Region of Bipartite and Tripartite Entanglement Switching

We study a quantum switch serving a set of users in a star topology. The function of the switch is to create bipartite or tripartite entangled state among users at the highest possible rates at a fixed ratio. We model a set of randomized switching policies. Discovering that some are better than others, we present analytical results for the case where the switch stores one qubit per user, and find that the best policies outperform a time division multiplexing (TDM) policy for sharing the switch between bipartite and tripartite state generation. This performance improvement decreases as the number of users grows. The model is easily augmented to study the capacity region in the presence of qubit decoherence, obtaining similar results. Moreover, decoherence appears to have little effect on capacity. We also study a smaller class of policies when the switch stores two qubits per user.

CONTINUOUS-VARIABLE QUANTUM TELEPORTATION OF MULTIPARTITE ENTANGLED COHERENT STATES

We investigate the problem of teleportation of tripartite entangled coherent state (ECS) using linear optical devices such as beam splitters, phase shifters, and two-mode number measurements. The scheme is based on the maximally four-partite ECS with bipartite maximal entanglement as the quantum channel to teleportation tripartite ECS. Our scheme is efficient in the sense that for mean number of photons equal to 2, the minimum of average fidelity (MAF) for teleportation an arbitrary tripartite entangled state is 1-2.3 × 10-7. We also generalize the tripartite scheme into multipartite case and calculate the MAF for the schemes in multipartite cases.

EFFICIENT QUANTUM CIRCUITS FOR PERFECT AND CONTROLLED TELEPORTATION OF n-QUBIT NON-MAXIMALLY ENTANGLED STATES OF GENERALIZED BELL-TYPE

An efficient and economical scheme is proposed for the perfect quantum teleportation of n-qubit non-maximally entangled state of generalized Bell-type. A Bell state is used as the quantum channel in the proposed scheme. It is also shown that the controlled teleportation of this n-qubit state can be achieved by using a GHZ state or a GHZ-like state as quantum channel. The proposed schemes are economical because for the perfect and controlled teleportation of n-qubit non-maximally entangled state of generalized Bell-type, we only need a Bell state and a tripartite entangled state respectively. It is also established that there exists a family of 12 orthogonal tripartite GHZ-like states which can be used as quantum channel for controlled teleportation. The proposed protocols are critically compared with the existing protocols.