XVIth International Workshop on
Quantum Systems in
Chemistry and Physics
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Quantum decoherence at the femtosecond level in liquids and solids observed in neutron Compton scattering
Erik B. Karlsson
Dept. of Physics and Astronomy
Uppsala University
Box 516
SE 75120 Uppsala
Sweden
About 10 years ago it was found that neutron scattering on hydrogen showed anomalously low cross-sections in many materials when it was observed under Compton scattering conditions (i.e. with neutron energies larger than 10 eV, where the duration of the scattering process falls in the τsc = 10-16 10-15 s range). The anomalies decreased with the neutron energy, which meant that the cross-sections approached normal values for long scattering times.

This phenomenon is interpreted here as due to an entanglement between the protons (because of their indistinguishability) during the scattering process, by which certain terms in the cross-section are cancelled through the large zero-point motion of the protons. The anomalies disappear gradually as the proton states decohere in contact with the local environment. Fitted decoherence times range from 4 10-15 s for proton pairs in liquid hydrogen to 5 10-16 s in metal hydrides. For the proton pairs in water, the data are compared with a theoretical estimate for decoherence based on the influence of fluctuations in hydrogen bonding to nearby molecules.

The fast decoherence of locally prepared entangled states in condensed media studied here is compared with decoherence (in the 10-6 - 10-3 s range) in objects studied in quantum optics in high vacuum, with the disapperance of the superposition state in NH3 or ND3 molecules in dilute gases, and with the lifetime of superconducting qubits in solids (10-9 s) at low temperature.



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