1203.0319 (F. Fröwis et al.)
F. Fröwis, W. Dür
We study quantum states produced by optimal phase covariant quantum cloners. We argue that cloned quantum superpositions are not macroscopic superpositions in the spirit of Schroedingers cat, despite their large particle number. This is indicated by calculating several measures for macroscopic superpositions from the literature, as well as by investigating the distinguishability of the two superposed cloned states. The latter rapidly diminishes when considering imperfect detectors or noisy states, and does not increase with system size. In contrast, we find that cloned quantum states itself are macroscopic, both in the sense of proposed measures and their usefulness in quantum metrology with an optimal scaling in system size. We investigate the applicability of cloned states for parameter estimation in the presence of different kinds of noise.
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http://arxiv.org/abs/1203.0319
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