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arXiv:1408.1978 · Physical Review Letters

Tm3+∶Y3Ga5O12 Materials for Spectrally Multiplexed Quantum Memories

Charles W. Thiel, Neil E. Sinclair, Wolfgang Tittel, R. L. Cone

Published Oct 13, 2014• 34 citations
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Abstract

We investigate the relevant spectroscopic properties of the 795 nm $^{3}{\mathrm{H}}_{6}\ensuremath{\leftrightarrow}^{3}{\mathrm{H}}_{4}$ transition in 1% ${\mathrm{Tm}}^{3+}\ensuremath{\mathbin:}{\mathrm{Y}}_{3}{\mathrm{Ga}}_{5}{\mathrm{O}}_{12}$ at temperatures as low as 1.2 K for optical quantum memories based on persistent spectral tailoring of narrow absorption features. Our measurements reveal that this transition has uniform coherence properties over a 56 GHz bandwidth, and a simple hyperfine structure split by $\ifmmode\pm\else\textpm\fi{}44\text{ }\text{ }\mathrm{MHz}/\mathrm{T}$ with lifetimes of up to hours. Furthermore, we find a ${^{3}\mathrm{F}}_{4}$ population lifetime of 64 ms---one of the longest lifetimes observed for an electronic level in a solid---and an exceptionally long coherence lifetime of $490\text{ }\text{ }\ensuremath{\mu}\mathrm{s}$---the longest ever observed for optical transitions of ${\mathrm{Tm}}^{3+}$ ions in a crystal. Our results suggest that this material allows realizing broadband quantum memories that enable spectrally multiplexed quantum repeaters.

DOI
10.1103/physrevlett.113.160501

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We investigate the relevant spectroscopic properties of the 795 nm 3H6\ensuremath↔3H4^{3}{\mathrm{H}}_{6}\ensuremath{\leftrightarrow}^{3}{\mathrm{H}}_{4}3H6​\ensuremath↔3H4​ transition in 1% Tm3+\ensuremath:Y3Ga5O12{\mathrm{Tm}}^{3+}\ensuremath{\mathbin:}{\mathrm{Y}}_{3}{\mathrm{Ga}}_{5}{\mathrm{O}}_{12}Tm3+\ensuremath:Y3​Ga5​O12​ at temperatures as low as 1.2 K for optical quantum memories based on persistent spectral tailoring of narrow absorption features. Our measurements reveal that this transition has uniform coherence properties over a 56 GHz bandwidth, and a simple hyperfine structure split by \ifmmode±\else\textpm\fi44  MHz/T\ifmmode\pm\else\textpm\fi{}44\text{ }\text{ }\mathrm{MHz}/\mathrm{T}\ifmmode±\else\textpm\fi44  MHz/T with lifetimes of up to hours. Furthermore, we find a 3F4{^{3}\mathrm{F}}_{4}3F4​ population lifetime of 64 ms---one of the longest lifetimes observed for an electronic level in a solid---and an exceptionally long coherence lifetime of 490  \ensuremathμs490\text{ }\text{ }\ensuremath{\mu}\mathrm{s}490  \ensuremathμs---the longest ever observed for optical transitions of Tm3+{\mathrm{Tm}}^{3+}Tm3+ ions in a crystal. Our results suggest that this material allows realizing broadband quantum memories that enable spectrally multiplexed quantum repeaters.
Decoherence of the 795 nm 3H6^{3}\mathrm{H}{}_{6}3H6​ to 3H4^{3}\mathrm{H}{}_{4}3H4​ transition in 11%{\mathrm{Tm}}^{3+}:{\mathrm{Y}}_{3}{\mathrm{Ga}}_{5}{\mathrm{O}}_{12}1 (Tm:YGG) is studied at temperatures as low as 1.2 K. The temperature, magnetic field, frequency, and time scale (spectral diffusion) dependence of the optical coherence lifetime is measured. Our results show that the coherence lifetime is impacted less by spectral diffusion than other known thulium-doped materials. Photon echo excitation and spectral hole burning methods reveal uniform decoherence properties and the possibility to produce full transparency for persistent spectral holes across the entire 56 GHz inhomogeneous bandwidth of the optical transition. Temperature-dependent decoherence is well described by elastic Raman scattering of phonons with an additional weaker component that may arise from a low density of glass-like dynamic disorder modes (two-level systems). Analysis of the observed behavior suggests that an optical coherence lifetime approaching 1 ms may be possible in this system at temperatures below 1 K for crystals grown with optimized properties. Overall, we find that Tm:YGG has superior decoherence properties compared to other Tm-doped crystals and is a promising candidate for applications that rely on long coherence lifetimes, such as optical quantum memories and photonic signal processing.
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Spectroscopy and Coherence of an Excited-State Transition in Tm3+^{3+}3+:YAlO3_33​ at Telecommunication Wavelength
We characterize spectroscopic and coherence properties of the 1451.37 nm excited-state zero-phonon line (ZPL) between the 3F4^{3}F_{4}3F4​ and the 3H4^{3}H_{4}3H4​ manifolds of a thulium-doped yttrium aluminum perovskite (Tm3+^{3+}3+:YAlO3_33​) crystal at temperatures around 1.5 K. We measure the absorption spectrum between the 3H6^{3}H_{6}3H6​ - 3F4^{3}F_{4}3F4​ and 3F4^{3}F_{4}3F4​ - 3H4^{3}H_{4}3H4​ manifolds, the inhomogeneous broadening of the 3F4^{3}F_{4}3F4​ - 3H4^{3}H_{4}3H4​ (excited-state) ZPL, and the lifetimes of the higher-lying and lower-lying excited states. We also investigate level shifts caused by the quadratic Zeeman interaction as well as spectral hole-burning spectra with varying magnetic fields, providing insights into hyperfine interactions. Using again spectral holes but also optical free induction decays (FIDs), we assess optical coherence times, finding a maximum of 4.75±0.07 μs4.75 \pm 0.07~μs4.75±0.07 μs at B=2T and low ion concentration in the 3F4^{3}F_{4}3F4​ level. Our results -- the first to demonstrate coherence of an excited-state transition in a rare-earth crystal -- suggest the possibility of exploiting such transitions for quantum technology.
Abstract 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 % Tm3+-doped yttrium gallium garnet (Tm:YGG), we report measurements of optical coherence and energy-level lifetimes of its 3H 6 ↔ 3 H4 transition at a temperature of around 500 mK and various magnetic fields. Using spectral hole burning (SHB), 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 SHB measurements reveal that due to spectral diffusion, the effective coherence time reduces to a few µs 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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