Absolute and relative stability of an optical frequency reference based on spectral hole burning in Eu$^{3+}$:Y$_2$SiO$_5$

摘要

We present and analyze four frequency measurements designed to characterizethe performance of an optical frequency reference based on spectral holeburning in \EuYSO. The first frequency comparison, between a single unperturbedspectral hole and a hydrogen maser, demonstrates a fractional frequency driftrate of $5 \times 10^{-18}$ s$^{-1}$. Optical-frequency comparisons between apattern of spectral holes, a Fabry-P\'erot cavity, and an Al$^+$ optical atomicclock show a short-term fractional frequency stability of $1 \times10^{-15}\tau^{-1/2}$ that averages down to $2.5^{+1.1}_{-0.5} \times 10^{-16}$ at $\tau= 540~s$ (with linear frequency drift removed). Finally, spectral hole patternsin two different \EuYSO crystals located in the same cryogenic vessel arecompared, yielding a short-term stability of $7 \times10^{-16} \tau^{-1/2}$that averages down to $5.5^{+1.8}_{-0.9} \times 10^{-17}$ at $\tau = 204$~s(with quadratic frequency drift removed).