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ABSTRACT:
We propose a reliable entanglement
measure for a two-mode squeezed
thermal state of the quantum electromagnetic field in terms of its
Bures distance to the set of all separable states of the same kind.
The requisite Uhlmann fidelity of a pair
of two-mode squeezed thermal
states is evaluated as the maximal transition probability between two
four-mode purifications. By applying the Peres-Simon criterion of
separability we find the closest separable state. This enables us
to derive an insightful expression of the amount of entanglement.
Then we apply this measure of entanglement
to the study of the
Braunstein-Kimble protocol of teleportation. We use as input state
in teleportation a mixed one-mode Gaussian state. The entangled state
shared by the sender (Alice) and the receiver (Bob) is taken to be
a two-mode squeezed thermal state. We find that the properties
of the teleported state depend on both the input state and the
entanglement of the two-mode resource state. As a measure
of the quality of the teleportation process, we employ the Uhlmann
fidelity between the input and output mixed one-mode Gaussian states.
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