Combined atomic clock with blackbody-radiation-shift-induced instability below 10−19 under natural environment conditions

Abstract

Abstract We develop a method of synthetic frequency generation to construct an atomic clock with blackbody radiation (BBR) shift uncertainties below 10−19 at environmental conditions with a very low level of temperature control. The proposed method can be implemented for atoms and ions, which have two different clock transitions with frequencies ν 1 and ν 2 allowing to form a synthetic reference frequency ν syn = (ν 1 − ɛν 2)/(1 − ɛ), which is absent in the spectrum of the involved atoms or ions. Calibration coefficient ɛ can be chosen such that the temperature dependence of the BBR shift for the synthetic frequency ν syn has a local extremum at an arbitrary operating temperature T 0. This leads to a weak sensitivity of BBR shift with respect to the temperature variations near operating temperature T 0. As a specific example, the Yb+ ion is studied in detail, where the utilized optical clock transitions are of electric quadrupole (S → D) and octupole (S → F) type. In this case, temperature variations of ±7 K lead to BBR shift uncertainties of less than 10−19, showing the possibility to construct ultra-precise combined atomic clocks (including portable ones) without the use of cryogenic techniques.