Environmental entanglement

The advantages of enhanced coupling between collective many-atom states and the radiation field have to be checked against the worry that these states are highly entangled if non-classical light is stored. Entangled states are very sensitive to decoherence and one could naively expect their lifetime to decrease with the number of atoms. It is therefore important to analyze the effect of unwanted environmental influences on the fidelity of the collective QM. 

Interactions between adjacent particles of condensed phases can lead to quantum correlations, quantum interference, entanglement and decoherence, delocalization and "Schrodinger s cat" states. Such effects are theoretically expected to be extremely short-lived, due to environmental disturbances. Therefore, it has been widely believed that they cannot be experimentally detected. However, based on previous theoretical work (cf. [Chatzidimitriou-Dreismann 1995 Chatzidimitriou-Dreismann 1997 (b)]), we proposed to detect QE in condensed systems by means of sufficiently "fast" scattering techniques. Particularly suitable for this purpose is the NCS method. Our NCS investigations (on liquid H2O - D2O mixtures [Chatzidimitriou-Dreismann 1997 (a)]) started 1995 and have provided, for the first time, direct experimental evidence of attosecond QE between a proton and its adjacent particles. 

Quantum coherence is extremely sensitive to environmental interactions. This is a main stumbling block in the attempts to build quantum computers, and in spite of the fact that such devices are planned to be based on very weakly interacting systems (entanglement of photons or atoms well isolated in cavities) it is extremely difficult to preserve coherence over a sufficiently large number of basic operations steps. Coherent states in molecules are still more perturbed, as displayed for instance by the difference between the spectra of NHs and AsHs gases [Omnes 1994], Here, the H-atom in NH3 is delocalized in a quantum superposition, being on both sides of the //.rplane, while the spatial coherence of the heavier As-atom disappears during the time of observation which results in quite different optical properties. 

To conclude, our general analysis, from first principles, indicates the remarkable possibility of scattering cross-section modification caused by environmental relaxation of the target states, Eq. (7), without appreciable extra broadening of the scattering line shape. This relaxation is an irreversible process and related to, or accompanied with, fast decoherence of the initial entanglement of the struck proton with its adjacent particles (electrons, and per-... 

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