Optical Investigations of Coherence and Relaxation Dynamics of a Thulium-doped Yttrium Gallium Garnet Crystal at sub-Kelvin Temperatures for Optical Quantum Memory

Kavli Affiliate: Wolfgang Tittel

| First 5 Authors: Antariksha Das, Mohsen Falamarzi Askarani, Jacob H. Davidson, Neil Sinclair, Joshua A. Slater

| Summary:

Rare-earth ion-doped crystals are of great interest for quantum memories, a
central component in future quantum repeaters. To assess the promise of 1$%$
Tm$^{3+}$-doped yttrium gallium garnet (Tm:YGG), we report measurements of
optical coherence and energy-level lifetimes of its $^3$H$_6$ $leftrightarrow$
$^3$H$_4$ transition at a temperature of around 500 mK and various magnetic
fields. Using spectral hole burning, we find hyperfine ground-level (Zeeman
level) lifetimes of several minutes at magnetic fields of less than 1000 G. We
also measure coherence time exceeding one millisecond using two-pulse photon
echoes. Three-pulse photon echo and spectral hole burning measurements reveal
that due to spectral diffusion, the effective coherence time reduces to a few
$mu$s over a timescale of around two hundred seconds. Finally, temporal and
frequency-multiplexed storage of optical pulses using the atomic frequency comb
protocol is demonstrated. Our results suggest Tm:YGG to be promising for
multiplexed photonic quantum memory for quantum repeaters.

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