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Journal of Physics Conference Series

Absence of entanglement effect on the decay dynamics of H(2p) pairs produced by VUV photodissociation of H2

Xavier Urbain, Arnaud Dochain, Clément Lauzin, B. Fabre

Published Sep 7, 2015• 5 citations
Publisher

Abstract

The effects of entanglement on the spontaneous decay of a pair of H(2 p ) previously observed by Tanabe et al. ( Phys. Rev. A 82 , 040101 (2010)) could not be reproduced despite careful determination of emission times with respect to the synchrotron bunch.
DOI
10.1088/1742-6596/635/11/112085

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In this article, the authors experimentally investigate the possibility to produce a pair of entangled photons from the photodissociation of H2{}_{2}2​. They study the dynamics of the two-photon emission and introduce a simple model, assuming a transition from Hund's case (a) to Hund's case (c), to reproduce the measured angular distributions satisfactorily.
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In this paper, as a continuation of our recent article demonstrating that the 2p atom pair is entangled in the H2 photodissociation [Phys. Rev. A 111, 023116 (2025)], we have discovered the origins of the entanglement for the 2p atom-pair state and obtained the entanglement entropies by origins. The same investigation has been carried out for the precursor molecular state of the 2p atom pair. The reason for the increase of the entanglement entropy during the dissociation from the precursor molecule into the H(2p) + H(2p) atom pair has been made clear.
We have measured the coincidence time spectra of two Lyman-α photons emitted by a pair of H(2p) atoms in the photodissociation of H 2 at the incident photon energy of 33.66 eV and at the hydrogen gas pressures of 0.40 Pa and 0.02 Pa, from which the angular distributions of two Lyman-α photons have been obtained. The experimental angular distributions indicate the generation of the entangled pair of H(2p) atoms as predicted by the theory of our group (Miyagi et al 2007 J. Phys. B 40 617) and the role of a new kind of reaction, i.e. the reaction of the entangled pair of H(2p) atoms with an H 2 molecule that efficiently changes the entanglement. It has turned out that more entangled pairs of H(2p) atoms survive at 0.02 Pa than at 0.40 Pa. The decay time constant in the coincidence time spectrum at 0.02 Pa is approximately half the lifetime of a single H(2p) atom, 1.60 ns, while the decay time constant at 0.40 Pa is in agreement with the lifetime of a single H(2p) atom. It follows that the decay faster than the lifetime of a single H(2p) atom originates from the entanglement in the pair of H(2p) atoms.
T. Tanabe et al. [Phys. Rev. A 82, 040101(R) (2010)] have experimentally demonstrated that the emission properties of unstable atoms in entangled and product states are different. The authors define an apparent decay time as a fitting parameter which falls below the lifetime of the single atom for entangled pairs. We argue that their results about coincidence time spectra are correct, but those concerning lifetimes cannot be considered conclusive because they assume the emission of photons by the two atoms to be independent processes, a doubtful hypothesis for entangled states. We suggest an improved evaluation of the lifetimes based on a rigorous approach, which demands some modifications of the experimental procedure.