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

Abstract

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.

Continuous operation of a bicolor thulium optical lattice clock

“…12) In this Letter, we extend the proposal of Katori to the 169 Tm atomic system and discuss several advantages of continuous longitudinal spectroscopy of the 1.14 μm clock transition. 13,14) As we have shown recently, 6) we can simultaneously probe two clock transitions which connect different hyperfine sublevels of the ground and upper clock states (see Fig. 1, inset).…”

“…10 15 1 2 for ultra-low expansion glass (ULE)-based systems. 5,6) Improving the optical clock's frequency stability will facilitate relativistic geodesy 7) and fundamental research. 8) There are several strategies to improve the frequency stability, including development of continuous optical atomic clocks (which are free from the Dick effect) and active optical clocks 9,10) based on superradiant atomic emission.…”

“…The pumping process was optimized in our existing thulium apparatus. 6,17) In a setup with longitudinal excitation, it is necessary to excite atoms in a well-defined spatial region(s). In the original proposal, 11) this was achieved by the spatially localized magnetic field which mixes the 3 P 1 and 3 P 0 states in 88 Sr.…”

176 Lu + clock comparison at the 10 −18 level via correlation spectroscopy

“…Comparisons between clock systems claiming this level of accuracy ( 39 , 40 ) have variations of the measured ratios that cannot be explained by the error budgets of the individual systems, which is compelling evidence that large systematic shifts are not being controlled to the levels claimed. Such problems are unlikely to occur for systems such as lutetium or thullium ( 41 ) for the simple fact that systematics are not large enough to cause such variations. The total shift and any single contribution given in Table 2 is, at most, at the level of the current measurement precision.…”

Atomic Clock States of Thulium have Near-Zero Electric Quadrupole Moment

“…This makes f − f transitions in lanthanides less susceptible to EQM interactions with the gradients of an external electric field [3]. Indeed, great progress has very recently been made in devising a transportable optical clock using the hyperfine levels of the ground-state f −f transition in thulium atoms [4][5][6][7]. The EQM interaction is nevertheless one of the sources of uncertainty in this type of atomic clock.…”