Measuring and analyzing excitation-induced decoherence in rare-earth-doped optical materials

Abstract

A method is introduced for quantitatively analyzing photon echo decay measurements to characterize excitation-induced decoherence resulting from the phenomenon of instantaneous spectral diffusion. Detailed analysis is presented that allows fundamental material properties to be extracted that predict and describe excitation-induced decoherence for a broad range of measurements, applications and experimental conditions. Motivated by the need for a method that enables systematic studies of ultra-low decoherence systems and direct comparison of properties between optical materials, this approach employs simple techniques and analytical expressions that avoid the need for difficult to measure and often unknown material parameters or numerical simulations. This measurement and analysis approach is demonstrated for the 3 H 6 to 3 H 4 optical transition of three thulium-doped crystals, Tm 3+ :YAG, Tm 3+ :LiNbO 3 and Tm 3+ :YGG, that are currently employed in quantum information and classical signal processing demonstrations where minimizing decoherence is essential to achieve high efficiencies and large signal bandwidths. These new results reveal more than two orders of magnitude variation in sensitivity to excitation-induced decoherence among the materials studied and establish that the Tm 3+ :YGG system offers the longest optical coherence lifetimes and the lowest levels of excitation-induced decoherence yet observed for any known thulium-doped material.

Dephasing mechanisms of optical transitions in rare-earth-doped transparent ceramics

“…The mechanism that is responsible for the contribution ion−ion is excitation-induced instantaneous spectral diffusion (ISD) [34][35][36][37]. Random frequency shifts are caused by changes in the local environments of the ions due to the change in an ion's electric dipole moment when it is optically excited to the 5 D0 state [14].…”

“…Specifically, in the host crystal Y 2 O 3 , only one other sample has yielded a narrower optical transition (290 Hz achieved in the 0.3% Eu 3+ :Y 2 O 3 used in the work of Refs. [26,27,39,57]). More importantly, the spectroscopic characterization of the contributing broadening mechanisms Here we present a breakdown of the broadening contributions for the 0.5% Eu 3+ sample without ZrO 2 that was treated with post-HIP annealing, which yielded a 3.2 ± 0.2 kHz linewidth (Fig.…”

“…A material that is extremely well suited for a detailed study of dephasing processes in transparent ceramics is Eu 3+ -doped Y 2 O 3 . In a high-quality single crystal, this material exhibits minimal additional dephasing compared to the T 1 limit and is well characterized [26,27]. Although a linewidth of 290 Hz has been observed [26], consistently achieving the required crystalline quality for such optical performance has been elusive.…”

“…In a high-quality single crystal, this material exhibits minimal additional dephasing compared to the T 1 limit and is well characterized [26,27]. Although a linewidth of 290 Hz has been observed [26], consistently achieving the required crystalline quality for such optical performance has been elusive. This is highlighted by the studies of different crystal growth techniques that showed that the homogeneous linewidth can vary from 2.4-42 kHz in some crystalline fibers [28,29].…”

Rare-earth doped transparent ceramics for spectral filtering and quantum information processing

“…A linear increase in linewidth with increasing excitation power is observed and related to an instantaneous spectral broadening due to ion-ion interactions. [27][28][29] The extrapolated zero power homogeneous linewidths are Γ h = 7.5 ± 0.2 kHz (corresponding to a coherence lifetime T 2 = 1/(πΓ h ) of 42 µs) at 3.5 K. The same value was found for the 1.0% sample without additives, while the 0.5% sample with additives showed a slightly larger homogeneous linewidth of 9.2 ± 0.6 kHz (T 2 = 35 µs). Even though those homogeneous linewidths are still about one order of magnitude larger than that observed in the very best crystal known (Γ h = 760 Hz), 20 they are in the lower range of values observed for Eu 3+ :Y 2 O 3 crystals (Γ h = 2.4 − 42 kHz 19 ) and considerably narrower than that previously reported in transparent ceramics Γ h = 59 kHz.…”