Optimal manipulations with qubits: Universal quantum entanglers

Warning

This publication doesn't include Institute of Computer Science. It includes Faculty of Informatics. Official publication website can be found on muni.cz.

Authors	BŮŽEK Vladimír HILLERY M.
Year of publication	2000
Type	Article in Periodical
Magazine / Source	Physical Review A
MU Faculty or unit	Faculty of Informatics
Citation
Web	http://publish.aps.org/abstract/PRA/v62/e022303
Field	Theoretical physics
Keywords	STATES; CLONING; SEPARABILITY; INFORMATION; ENSEMBLES
Description	We analyze various scenarios for entangling two initially unentangled qubits. In particular, we propose an optimal universal entangler that entangles a qubit in unknown state \psi] with a qubit in a reference (known) state \0]. That is, our entangler generates the output state that is as close as possible to the pure (symmetrized) state (\psi]\0]+\0]\psi]). The most attractive feature of this entangling machine, is that the fidelity of its performance (i.e., the distance between the output and the ideally entangled-symmetrized state) does not depend on the input and takes the constant value F = (9 + 3 root 2)/14 similar or equal to 0.946. We also analyze how to optimally generate from a single qubit initially prepared in an unknown state \psi]) a two qubit entangled system, which is as close as possible to a Bell state (\psi]\psi(perpendicular to)]+\psi(perpendicular to)]\psi]), where [psi\psi(perpendicular to)] = 0.
Related projects:	Informatics as the third methodology Non-sequential Models of Computing -- Quantum and Concurrent Distributed Models of Computing