Simultaneous bicolor interrogation in thulium optical clock providing very low systematic frequency shifts.

Optical atomic clocks have already overcome the eighteenth decimal digit of instability and uncertainty, demonstrating incredible control over external perturbations of the clock transition frequency. At the same time, there is an increasing demand for atomic (ionic) transitions and new interrogation and readout protocols providing minimal sensitivity to external fields and possessing practical operational wavelengths. One of the goals is to simplify the clock operation while maintaining the relative uncertainty at a low 10-18 level achieved at the shortest averaging time. This is especially important for transportable and envisioned space-based optical clocks. Here, we demonstrate implementation of a synthetic frequency approach for a thulium optical clock with simultaneous optical interrogation of two clock transitions. Our experiment shows suppression of the quadratic Zeeman shift by at least three orders of magnitude. The effect of the tensor lattice Stark shift in thulium can also be reduced to below 10-18 in fractional frequency units. This makes the thulium optical clock almost free from hard-to-control systematic shifts. The "simultaneous" protocol demonstrates very low sensitivity to the cross-talks between individual clock transitions during interrogation and readout.

Mass selective laser cooling of 229Th3+ in a multisectional linear Paul trap loaded with a mixture of thorium isotopes.

We consider an experiment on trapping and laser cooling of 229Th3+ ions in a linear Paul trap in the presence of undesirable impurities such as ions of the radioactive isotope 228Th3+. We suggest a method of separating these impurities by means of selective laser cooling utilizing the isotope shift of cooling transitions in 229Th3+ and 228Th3+ ions. According to our estimation, the isotope shift is equal to 3.4 GHZ and makes laser separation of these isotopes possible.

Loading of mass spectrometry ion trap with Th ions by laser ablation for nuclear frequency standard application.

We describe an original multisectional quadrupole ion trap aimed to realize nuclear frequency standard based on the unique isomer transition in thorium nucleus. It is shown that the system effectively operates on Th+, Th2+ and Th3+ ions produced by laser ablation of metallic thorium-232 target. Laser intensity used for ablation is about 6 GW/cm2. Via applying a bias potential to every control voltage including the RF one, we are able not only to manipulate ions within the energy range as wide as 1-500 eV but to specially adjust trap potentials in order to work mainly with ions that belong to energy distribution maximum and therefore to effectively enhance the number of trapped ions. Measurement of energy distributions of 232Th+, 232Th2+, 232Th3+ ions obtained by laser ablation allows us to define optimal potential values for trapping process. Observed number of ions inside trap in dependence on trapping time is found to obey an unusually slow - logarithmic decay law that needs more careful study.