We consider a narrow magneto-dipole transition in the 169 Tm atom at the wavelength of 1.14 µm as a candidate for a 2D optical lattice clock. Calculating dynamic polarizabilities of the two clock levels [Xe]4f13 6s 2 (J = 7/2) and [Xe]4f 13 6s 2 (J = 5/2) in the spectral range from 250 nm to 1200 nm, we suggest the "magic" wavelength for the optical lattice at 807 nm. Frequency shifts due to blackbody radiation (BBR), the van der Waals interaction, the magnetic dipole-dipole interaction, and other effects which can perturb the transition frequency are calculated. The transition at 1.14 µm demonstrates low sensitivity to the BBR shift corresponding to 8 × 10 −17 in fractional units at room temperature which makes it an interesting candidate for high-performance optical clocks. The total estimated frequency uncertainty is less than 5 × 10 −18 in fractional units. By direct excitation of the 1.14 µm transition in Tm atoms loaded into an optical dipole trap, we set the lower limit for the lifetime of the upper clock level [Xe]4f 13 6s 2 (J = 5/2) of 112 ms which corresponds to a natural spectral linewidth narrower than 1.4 Hz. The polarizability of the Tm ground state was measured by the excitation of parametric resonances in the optical dipole trap at 532 nm.

One of the key systematic effects limiting the performance of state-of-the-art optical clocks is the blackbody radiation (BBR) shift. Here, we demonstrate unusually low sensitivity of a 1.14 μm inner-shell clock transition in neutral Tm atoms to BBR. By direct polarizability measurements, we infer a differential polarizability of the clock levels of −0.063(30) atomic units corresponding to a fractional frequency BBR shift of only 2.3(1.1) × 10 −18 at room temperature. This amount is several orders of magnitude smaller than that of the best optical clocks using neutral atoms (Sr, Yb, Hg) and is competitive with that of ion optical clocks (Al + , Lu + ). Our results allow the development of lanthanide-based optical clocks with a relative uncertainty at the 10 −17 level.

We report a new measurement of the n ¼ 2 Lamb shift in Muonium. Our result of 1047.2ð2.3Þ stat ð1.1Þ syst MHz comprises an order of magnitude improvement upon the previous best measurement. This value matches the theoretical calculation within 1 standard deviation allowing us to set limits on Lorentz and CPT violation in the muonic sector, as well as on new physics coupled to muons and electrons which could provide an explanation of the muon g − 2 anomaly.