Decoherence and absorption of Er3+:KTiOPO4 (KTP) at 1.5 μm

Abstract

We present results of laser absorption spectroscopy and two-pulse photon echo decoherence measurements on the lowest 4 I 15/2 to lowest 4 I 13/2 transition in Er 3+ :KTiOPO 4 (KTP-potassium titanyl phosphate) for the optical transition located at 1537.238 nm. This transition was found to have an inhomogeneous absorption linewidth of 950 MHz and pronounced polarization dependence. Two-pulse photon echo decay measurements as a function of applied magnetic field strength at 1.9 K revealed a narrow homogeneous linewidth of 2.5 kHz at 0.2 T that increased to 5.8 kHz at 1.2 T and then decreased to 1.6 kHz at 4.5 T. This behavior was successfully described by decoherence due to Er 3+-Er 3+ magnetic dipole interactions. Significant superhyperfine coupling of Er 3+ spins to the nuclear moments of ions in the host lattice was observed, modulating the photon echo decay at low magnetic fields and limiting the effective homogenous linewidth at high fields. Combined with the well-established potential of KTP for fabrication of high-quality optical waveguides and integrated non-linear frequency conversion, our results suggest that Er 3+ :KTP is a promising material system for practical spectral hole burning, signal processing, and quantum information applications.

Optical spectroscopy and decoherence studies ofYb3+:YAG at 968 nm

“…In the frequency domain, spectral diffusion causes the spectral hole to broaden over time, while in the time domain it leads to a progressive increase in the rate of phase decoherence that manifests itself in non-exponential decays. [66,73,74] To account for the effects of spectral diffusion on the photon echo decays, we used the empirical Mims function describing the echo intensity I as a function of pulse separation between pulse 1 and 2 as t 12 as ( )…”

“…11 has been observed in other paramagnetic rare-earth materials and is a general feature of spectral diffusion caused by phonon-driven electron spin flips. [74,77,78,79] The local maximum in the magnetic field dependence of the effective homogeneous linewidth can be quantitatively predicted based on the magnetic dipole-dipole interactions between Yb 3+ ions. When an Yb 3+ ion spin changes its orientation, it causes a small shift in the magnetic field strength for all other Yb 3+ ions in its environment and hence slightly shifts their transition frequencies by a random amount that depends on their relative position in the crystal.…”

Optical decoherence and spectral diffusion in an erbium-doped silica glass fiber featuring long-lived spin sublevels

“…This behavior has been attributed to spectral diffusion due to the interaction of Er 3+ ions with magnetic TLS 11,12 , or other Er 3+ ions in the environment 15 . The latter process is regularly observed in Er 3+ -doped crystals [18][19][20] . In the region of low magnetic field, we observe a local minimum at B ≈ 0.05 T, followed by a local maximum at B ≈ 0.15 T. This behavior is similar to what has been observed in Er 3+ -doped crystals, such as Er 3+ :LiNbO 3 and Er 3+ :KTP 19,20 , and can be explained by the competition between two mechanisms: the interaction between Er 3+ ions, which decreases with B, and the interaction between Er 3+ ions and resonant TLS, which increases with B according to the TLS density of states 6 .…”

Modification of phonon processes in nanostructured rare-earth-ion-doped crystals

“…The R 0 term is negligible in Er:LiNbO 3 [31], whereas the spin flip-flop rate is very small for Er:Y 2 SiO 5 [20]. Er:KTiOPO 4 has unusually small R 0 and weak spin flip-flop process, so that only the direct phonon process significantly contributes to the field-dependent spectral diffusion, even at low field strengths [32]. However, in all cases the direct phonon process becomes dominant for magnetic field strengths of 1 T and higher.…”

“…Three important cases are Er 3+ :Y 2 SiO 5 , for which optical coherence lifetimes of up to 4.4 ms have been observed [30], Er 3+ :LiNbO 3 , exhibiting a large oscillator strength accompanied by a very broad inhomogenous linewidth [31], and Er 3+ :KTiOPO 4 , which has shown narrow homogeneous linewidths down to 1.6 kHz [32]. All Er-doped crystals so far eluded efficient quantumstate storage [31,[33][34][35] since no efficient persistent hole burning involving electronic Zeeman levels [36] has been achieved.…”