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, 41 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.
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
