Tunable Solid-State Quantum Memory Using Rare-Earth-Ion-Doped Crystal, Nd3+:GaN

Report No. ARL-TR-8009
Authors: S Rudin, BC Connelly, VS Malinovsky, RW Enck, and GD Metcalfe
Date/Pages: April 2017; 44 pages
Abstract: The research objective of this Director's Research Initiative was to work on developing solid-state quantum memory using cryogenically cooled rare-earth-ion-doped crystal, Nd3+:GaN. The samples were grown using the US Army Research Laboratory's molecular beam epitaxy (MBE) capabilities. The approach is based on the coherent transient interaction between light and the ions in a semiconductor. We investigated the energy level structure of the neodymium (Nd) ions embedded into the semiconductor crystal lattice, gallium nitride (GaN), and developed a quantum description of the 2- and 3-pulse photon echo effect. Epitaxial GaN:Nd was grown by plasma-assisted molecular beam epitaxy in a modular Gen II reactor using liquid gallium, solid Nd, and a nitrogen plasma. The photoluminescence (PL) spectrum from the lowest 4F3/2 multiplet to all 4I9/2 multiplets was measured by a free-space variable amplifier silicon diode. A demonstration of the coherence properties requires a high-quality sample with a narrow homogeneous broadening. For this reason, the PL linewidth was characterized for various growth conditions. The experiments were carried out to observe coherent effects, and various experimental setups are described. In parallel with experiments on the coherence properties of Nd3+:GaN, we also investigated the effect of a varying electric field on the Nd PL spectrum to provide a tunable memory. To vary the applied field, we designed and grew a series of Nd-doped GaN p-i-n structures, strain-balanced superlattice structures, and periodic unbalanced structures.
Distribution: Approved for public release
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Last Update / Reviewed: April 1, 2017