Speaker
Description
Rare-earth ions in crystalline hosts are promising candidates for quantum memory applications, offering long-lived nuclear spin states and frequency compatibility with superconducting quantum circuits. A key factor limiting spin coherence in these systems is the interaction of the electron spin with the surrounding nuclear spin bath, the superhyperfine (SHF) interaction, which can be also exploited for longer storage of coherence into the nuclear spin states. We investigate the SHF interaction of ¹⁷¹Yb³⁺ and ¹⁷³Yb³⁺ impurity ions co-doped in an Er:⁷LiYF₄ crystal at millikelvin temperatures using broadband electron spin resonance spectroscopy based on superconducting coplanar waveguides. By sweeping an external magnetic field from zero to 50 mT with the field applied along the crystal c-axis, we map the spin transition spectra and resolve their SHF substructure arising from the eight nearest-neighbor ¹⁹F nuclei in the S₄ site symmetry of LiYF₄. Complementary measurements with the field perpendicular to the c-axis are also performed. We identify Zero First-Order Zeeman (ZEFOZ) transitions and characterize their spectral positions. Spin Hamiltonian simulations are overlaid on the two-dimensional experimental spectra, allowing direct comparison. Pulsed spin echo measurements are performed near the ZEFOZ transitions, where free induction decay signals are observed and Hahn echo sequences aim to characterize the coherence time T₂.
