Robust optical clock transitions in trapped ions using dynamical decoupling

Abstract

Wepresent a novel method for engineering an optical clock transition that is robust against externalfield fluctuations and is able to overcome limits resulting fromfield inhomogeneities.The technique is based on the application of continuous drivingfields to form a pair of dressed states essentially free of all relevant shifts. Specifically, the clock transition is robust to magnetic field shifts, quadrupole and other tensor shifts, and amplitude fluctuations of the driving fields.The schemeis applicable to either a single ion or an ensemble of ions, and is relevant for several types of ions, such as 40Ca+ , 88Sr+ , 138Ba+ and 176Lu+ .Taking a spherically symmetricCoulomb crystal formed by 400 40Ca+ ions as an example,we showthrough numerical simulations that the inhomogeneous linewidth of tens ofHertz in such a crystal together with linear Zeeman shifts of order 10MHzare reduced to forma linewidth of around 1Hz.We estimate a twoorder- of-magnitude reduction in averaging time compared to state-of-the art single ion frequency references, assuming a probe laser fractional instability of10-15. Furthermore, a statistical uncertainty reaching 2.9×10−16 in 1s is estimated for a cascaded clock scheme inwhich the dynamically decoupled Coulomb crystal clock stabilizes the interrogation laser for an 27Al+ clock.