Electromagnetically induced transparency in an isotopically purified ${\mathrm{Nd}}^{3+}:{\mathrm{YLiF}}_4$ crystal

We report the first observation of electromagnetically induced transparency (EIT) in an isotopically purified ${\mathrm{Nd}}^{3+}:{\mathrm{YLiF}}_4$ crystal. This crystal demonstrates inhomogeneous broadening of optical transitions of about 35 MHz. EIT is observed in a symmetrical $\mathrm{\Lambda }$-like system formed by two hyperfine sublevels of the ground state corresponding to a zero first-order Zeeman (ZEFOZ) transition and a hyperfine sublevel of the excited state, which is not coupled to other ground-state sublevels. It is found that transmission of the probe field as a function of the two-photon detuning demonstrates a comblike structure that can be attributed to superhyperfine coupling between ${\mathrm{Nd}}^{3+}$ ions and fluorine nuclei. The observed structure can be resolved only in the vicinity of the ZEFOZ point where the homogeneous linewidth of the spin transition is sufficiently small. The results pave the way for implementing solid-state quantum memories based on off-resonant Raman interaction without spectral tailoring of optical transitions.

Figure 1

Absorption spectra of the sample on the ${}^4\mathrm{I}_{9/2}\left(1\right)-{}^4\mathrm{F}_{3/2}\left(1\right)$ transition in the absence of an external magnetic field (above) and in an external longitudinal magnetic field of 60.5 mT (below). The resonant lines 1 and 2 form the $\mathrm{\Lambda }$ system that was used for EIT.

Figure 2

Left: Hyperfine structure of the electronic ground and excited states as a function of the longitudinal magnetic field. Right: hyperfine sublevels forming the identified ideal $\mathrm{\Lambda }$ system at magnetic field of 63.6 mT (above) and the two-photon transition frequency $\mathrm{\Delta }{\omega }_{12}={\omega }_{12}-{\omega }_{12}^0$ as a function of longitudinal and transverse magnetic field deviation from the ZEFOZ point (below).

Figure 3

Schematic of the experimental setup.

Figure 4

The dependence of the two-photon transition frequency ${\omega }_{AB}$ (squares) and of the EIT amplitude (circles) on the external magnetic field in the vicinity of the ZEFOZ point. The coupling field intensity is around 50 W/${\mathrm{cm}}^2$.

Figure 5

Left: EIT feature profile for different values of external magnetic field. The coupling field intensity is around 7 W/${\mathrm{cm}}^2$. Right: EIT feature profile for different intensities of the pump field. The crystal is located close to the beam focal point (beam waist around 100 $\mu \mathrm{m}$) and the external magnetic field is 63.6 mT. $\mathrm{\Delta }f$ is the frequency detuning of the probe field from the coupling field.