Observation of Photon Echoes From Evanescently Coupled Rare-Earth Ions in a Planar Waveguide

We report the measurement of the inhomogeneous linewidth, homogeneous linewidth, and spin-state lifetime of ${\mathrm{Pr}}^{3+}$ ions in a novel waveguide architecture. The ${\mathrm{TeO}}_2$ slab waveguide deposited on a bulk ${\mathrm{Pr}}^{3+}:{\mathrm{Y}}_2{\mathrm{SiO}}_5$ crystal allows the ${{}^3\mathrm{H}}_4{\leftrightarrow }^1{\mathrm{D}}_2$ transition of ${\mathrm{Pr}}^{3+}$ ions to be probed by the optical evanescent field that extends into the substrate. The 2-GHz inhomogeneous linewidth, the optical coherence time of $70\pm 5\mu \mathrm{s}$, and the spin-state lifetime of $9.8\pm 0.3\mathrm{s}$ indicate that the properties of ions interacting with the waveguide mode are consistent with those of bulk ions. This result establishes the foundation for large, integrated, and high performance rare-earth-ion quantum systems based on a waveguide platform.

Figure 1

A simple example of a device utilizing the proposed architecture for integrated rare-earth-ion quantum systems. Electrodes are incorporated with a waveguide-based platform to control individual components through the linear Stark shift of the ions. Two photon echo devices are shown in (a). When the voltage is switched from low to high, the ions are shifted from $f_0$ into resonance with the excitation laser frequency $f_{\text{laser}}$ (b). Panels (c) and (d) show an indicative time evolution of the applied voltage and waveguide output for the two photon echo devices. In (d) the absorption of the $\pi /2$ and $\pi$ pulses decreases the output intensity and the photon echoes modulate the waveguide output because the coherent emission is at $f_0$.

Figure 2

(a) Crystalline axes relative to the film deposition. (b) The electric field amplitude $E_x$ of the fundamental TE mode supported by the 400-nm ${\mathrm{TeO}}_2$ film waveguide on a ${\mathrm{Pr}}^{3+}:{\mathrm{Y}}_2{\mathrm{SiO}}_5$ crystal substrate. (c) Experimental setup inside the cryostat used to perform the characterization of the ${\mathrm{TeO}}_2$ on ${\mathrm{Pr}}^{3+}:{\mathrm{Y}}_2{\mathrm{SiO}}_5$ waveguide.

Figure 3

The absorption spectrum of the 0.005% ${\mathrm{Pr}}^{3+}:{\mathrm{Y}}_2{\mathrm{SiO}}_5$ substrate probed by the evanescent field from light guided in the thin ${\mathrm{TeO}}_2$ film waveguide.

Figure 4

Photon echo intensity as a function of the delay time $\tau$.

Figure 5

Stimulated echo intensity as a function of the delay between writing and probing the grating. The measured decay time of the echo amplitude $T_g=9.8\pm 0.3\mathrm{s}$ is representative of the lifetime ($T_1$) of a subset of the hyperfine spin states.