2020 Impact factor 1.425
Atomic, Molecular, Optical and Plasma Physics
Eur. Phys. J. D 56, 141-150 (2010)
DOI: 10.1140/epjd/e2009-00270-x

Quantum entanglement in a soluble two-electron model atom

R.J. Yañez1, 2, A.R. Plastino1, 3, 4 and J.S. Dehesa1, 4

1  Instituto Carlos I de Física Teórica y Computacional, Universidad de Granada, 18071 Granada, Spain
2  Departamento de Matemática Aplicada, Universidad de Granada, 18071 Granada, Spain
3  National University La Plata, UNLP-CREG, Casilla de Correo 727, La Plata 1900, Argentina
4  Departamento de Física Atómica, Molecular y Nuclear, Universidad de Granada, 18071 Granada, Spain

arplastino@maple.up.ac.za

Received 12 March 2009 / Received in final form 23 August 2009 / Published online 6 November 2009

Abstract
We investigate the entanglement properties of bound states in an exactly soluble two-electron model, the Moshinsky atom. We present exact entanglement calculations for the ground, first and second excited states of the system. We find that these states become more entangled when the relative inter-particle interaction becomes stronger. As a general trend, we also observe that the entanglement of the eigenstates tends to increase with the states' energy. There are, however, “entanglement level-crossings” where the entanglement of a state becomes larger than the entanglement of other states with higher energy. In the limit of weak interaction, we also compute (exactly) the entanglement of higher excited states. Excited states with anti-parallel spins are found to involve a considerable amount of entanglement even for an arbitrarily weak (but non zero) interaction. This minimum amount of entanglement increases monotonically with the state's energy. Finally, the connection between entanglement and the Hartree-Fock approximation in the Moshinsky model is addressed. The quality of the ground-state Hartree-Fock approximation is shown to deteriorate, and the corresponding correlation energy to grow, as the entanglement of the (exact) ground state increases. The present work goes beyond previous related studies because we fully take into account the identical character of the two constituting particles in the entanglement calculations, and provide analytical, exact results both for the ground and the first few excited states.

PACS
03.65.-w - Quantum mechanics.
03.67.-a - Quantum information.
03.67.Mn - Entanglement measures, witnesses, and other characterizations.

© EDP Sciences, Società Italiana di Fisica, Springer-Verlag 2009