Development of optical atomic clocks based on neutral titanium atoms

Optical atomic clocks have taken a giant leap in recent years, with several experiments reaching uncertainties at the 10⁻¹⁸ level. The leading neutral-atom optical clocks operate on wavelengths of 698 nm (Sr) and 578 nm (Yb). Light at these wavelengths is strongly attenuated in optical fibers, posing a challenge to long-distance time transfer. These wavelengths are also inconvenient for constructing the ultrastable lasers that are an essential component of optical clocks. Using neutral titanium atoms for optical clocks allow us to operate in the telecommunication wavelength band that has a clear advantages: the S-, C- and L-bands, ranging altogether between about 1460 and 1625 nm, feature low losses in standard optical fibers.

We propose the use of ultra-narrow optical transitions in atomic titanium (Ti) as the basis of a telecommunications-band atomic clock. We found several transitions between the 3d²4s² a ³F and 3d³(⁴F )4s a ³F fine structure manifolds in Ti with transition wavelengths between 1483 and 1610 nm and that can serve as optical clock references for ultrastable telecommunication-band light sources.

From a numerical calculation of the Ti level structure, we identify a few key features that make Ti an attractive atom for clock applications: the extreme narrowness of the candidate clock transitions, a weak clock sensitivity to blackbody radiation shifts, and the existence of several magic wavelengths for optical trapping. All relevant properties were calculating using a high-precision relativistic hybrid method that combines configuration interaction (CI) and coupled cluster (CC) approaches. To identify magic wavelengths, we have completed the largest-to-date direct dynamical polarizability calculations.

The atomic titanium, as a transition-metal element, can be laser-cooled on near-cycling optical transitions, allowing for the adoption of optical lattice or tweezer trapping techniques used in today’s leading neutral-atom clocks. To enable implementation of the optical tweezers system, we have computed the dynamic polarizabilities for 3d²(³F )4s4p(³P^o) z⁵G^o₆ and 3d³(⁴F )4p y⁵G^o₆ states of a neutral titanium atom at a laser wavelength of 750 nm.