A Multi-Ion Photonic Integrated Optical Clock

Optical atomic clocks based on single trapped ions boast impressive stability and accuracy, but extension to multiple co-trapped ions is hindered by their strong Coulomb repulsion and associated quadrupole shifts. An alternative path is to multiplex the entire trapping apparatus, a feat made accessible by chip scale traps with photonic integration. This multiplicity brings new opportunities for improved short-term stability, Dick-noise suppression, and simultaneous Zeeman sublevel interrogation. While chip traps bring challenges for clock operation, particularly with regard to motional excitation, they also offer greater control over blackbody radiation and a clearer path towards portability. We explore these new opportunities with multiple $^{88}$Sr$^+$ ions loaded in separate zones of a fully photonic integrated chip trap and clocked on the $^5S_{1/2}$ to $^4D_{5/2}$ forbidden optical transition.