Optimal manipulations with qubits: Universal quantum entanglers

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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