Atomic Clocks with Suppressed Blackbody Radiation Shift

We develop a concept of atomic clocks where the blackbody radiation shift and its fluctuations can be suppressed by 1--3 orders of magnitude independent of the environmental temperature. The suppression is based on the fact that in a system with two accessible clock transitions (with frequencies ν₁ and ν₂) which are exposed to the same thermal environment, there exists a ``synthetic'' frequency νsyn ∝ (ν₁-ε₁₂ν₂) largely immune to the blackbody radiation shift. For example, in the case of ¹⁷¹Yb⁺ it is possible to create a synthetic-frequency-based clock in which the fractional blackbody radiation shift can be suppressed to the level of 10^-18 in a broad interval near room temperature (300±15 K). We also propose a realization of our method with the use of an optical frequency comb generator stabilized to both frequencies ν₁ and ν₂, where the frequency νsyn is generated as one of the components of the comb spectrum.