Thulium is great for optical clocks.
1. Narrow inner-shell transition: 1.2 Hz.
2. Low sensitivity to BBR: 0.6 mHz shift @ room temperature.
3. Magic wavelength near 1064 nm.
4. Total shift is less than 5x10-17.
Optics department at Lebedev Physical Institute first embarked on thulium project in 2008. Since then we were first to laser cool it, perform precise spectroscopy of relevant energy levels, find clock transition, determine magic wavelength, and narrow the absorption spectrum of the clock transition down to Fourier limit.
We have an amazing team of researches that made the whole project possible. Good team spirit is an essential part of any successful research and we are lucky to have it!