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Research in Optical Sciences

Heralded Quantum Entanglement between two Rare-Earth-Ion Doped Crystals

Christoph Clausen, Imam Usmani, Félix Bussières, Nicolas Sangouard, Mikael Afzelius, Nicolas Gisin

Published Jan 1, 2012• 1 citation
Publisher

Abstract

Two rare-earth-ion doped crystals were entangled by converting a single photon into a delocalized excitation. The excitation was subsequently converted back into a photon and the entanglement revealed by an estimation of the concurrence.
DOI
10.1364/qim.2012.qt3a.5

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Entanglement between single spins and photons is an important resource in quantum information science, e.g. in quantum networking. Rare-earth ions in dielectric crystals have emerged as a promising candidate for this task. Rare-earth ion doped solids have been used so far mostly as ensemble-based quantum memories. However, they also feature promising properties for single ion detection and manipulation, such as long-lived spins, narrow optical transitions and preservation of coherence properties when inserted in nanostructures. Because of the long lifetimes of the optical t
The experimental work of Imam Usmani, Christoph Clausen, Félix Bussières, Nicolas Sangouard, Mikael Afzelius, and Nicolas Gisin, published in Nature Photonics in 2012 under the title “Heralded Quantum Entanglement between Two Crystals,” demonstrated heralded entanglement between two spatially separated solid-state quantum memories formed by rare-earth-ion ensembles (Usmani et al. 2012). A heralded single photon was placed in a path-entangled state and subsequently mapped onto two N d3+ : Y2SiO5 crystals. After a predetermined storage interval, the collective matter excitation was converted back into optical fields, whose interference properties and concurrence estimates provided evidence for entanglement between the memories. The experiment is particularly relevant to the Theory of Objectivity (TO) because the TO assigns foundational significance to individualization, boundaries, relational existence, composition, atomic relations, information, and radiation (Cabannas and Silva 2016, 2018, 2025). This article develops a critical–propositional dialogue between the Usmani ex- periment and the modal architecture of the Theory of Objectivity. Particular attention is devoted to the First Absolute Truth, according to which the pre-universal Nothing is not absolute non-being but an eternal logical and mathematical essence; the Second Ab- solute Truth, according to which every existing element possesses a unique intrinsic field that individualizes it; the Fifth Absolute Truth, according to which an element requires relational observation by at least two other elements rather than human observation; and the Seventh Absolute Truth, according to which knowledge or information produced through atomic relations constitutes the transcendent element and is associated, within the TO framework, with atomic radiation. The analysis finds no direct empirical contact between Usmani et al. and the First or Third Absolute Truths. It identifies meaningful but incomplete compatibility with the Second, Fourth, and Fifth Absolute Truths, strong compositional compatibility with the Sixth, and the most significant phenomenological bridge with the Seventh. The experimentally realized sequence radiation −→ collective atomic excitation −→ radiation shows that quantum information initially carried by light can be mapped onto collective atomic degrees of freedom and subsequently recovered in optical form. This result constitutes a scientifically relevant bridge for the TO proposition connecting information, atomic relations, and radiation. Nevertheless, it does not demonstrate that information is ontologically identical to a transcendent substance, nor does it establish the modal necessity of the Seven Absolute Truths. The article therefore distinguishes empirical compatibility, indirect corroboration, operational bridge-building, direct testing, and exclusive confirmation. It concludes by proposing measurable TO-inspired variables and experiments capable of converting interpretive parallels into differential predictions. A final appendix presents the analysis in a TO-style modal–operational format. Keywords: Theory of Objectivity; heralded entanglement; quantum memory; rare- earth-ion crystals; atomic frequency comb; quantum information; atomic radiation; transcendent information; relational ontology; modal necessity; quantum networks; boundaries; Inducer Effects; cosmological eras.
Probe field amplification without population inversion in a one-dimensional photonic crystal (1DPC) doped by four-level rare-earth ions is proposed. By controlling the intensity of the coupling field, probe field absorption with population inversion converts to probe field amplification without population inversion. It is found that the amount of probe field amplification through the photonic crystal doped by rare-earth ions is larger than the probe field amplification for the same ions in free space. For a particular coupling field intensity, i.e. Ωc=5.1Γ, the probe field absorption converts to probe field amplification just by manipulating the probe field detuning.