Nanooptics and Photonics

Rare earth ions optical centers in inorganic phosphors: from single to entangled states prospective for quantum computing

Vinogradova E.1, Vagapova E.1,2, Dolgov L.1, Orlovskii Yu.1,2
1 Institute of Physics, University of Tartu, W. Ostwaldi str, 1, Tartu-50411, Estonia 
E-mail: elena.vinogradova@ut.ee
2 Prokhorov General Physics Institute, Russian Academy of Sciences, 38 Vavilov str, Moscow-119991, Russia 

Initial interest to inorganic crystals doped by Nd3+ ions was caused by their importance for laser applications. Nd3+ ions give narrow near infrared luminescence spectral lines associated with optical transitions of 4f electrons from the 4F3/2 energy level. Luminescence of Nd3+ ions from higher-lying energy levels is usually quenched by multiphonon relaxation or by cross-relaxation non-radiative energy transfer between neighbouring Nd3+ ions [1].
Here luminescence of LaF3:Nd3+ crystal was investigated at liquid helium temperatures (1.8 - 7K) under tunable narrow line selective laser excitation. Besides intensive spectral lines associated with single-site Nd3+ optical centers, weak satellite spectral lines caused by pairs of Nd3+ ions were detected. In contrast to Ref. [2] selection both by excitation in the range 577-579 nm and by emission in the range of 860-862 nm was done. This in combination with luminescence kinetics measurements allowed distinguishing excitation and luminescence spectral lines from different pairs of Nd3+ ions. Revealed specific splitting of excitation spectral lines at the 4I9/2 → 4G5/2 transition is connected with lifting of Kramers degeneration for crystal-field energy levels of Nd3+ ions. Such splitting is associated with formation of quantum entangled states in pairs of Nd3+ ions, which can be potentially used for C-NOT gate of quantum computer [3].
Acknowledgment: The work was made under support of Estonian Research Council project PRG347.

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