A cryogenic sapphire resonator oscillator with 10(-16) mid-term fractional frequency stability

We report in this Letter the outstanding frequency stability performance of an autonomous cryogenic sapphire oscillator (CSO) presenting a flicker frequency noise floor below 2 x 10(-16) near 1000 s of integration time and a long-term Allan deviation limited by a random walk process of similar to 1 x 10(-18) root tau. The frequency stability qualification at this level called for the implementation of sophisticated instrumentation associated with ultra-stable frequency references. This result is technologically sound as it demonstrates the potentiality of the CSO technology. From the physical point of view, it sets an upper limit to the ultimate noise floor of the cryogenic microwave resonator that is competitive to that of the ultra-stable optical Fabry-Perot cavities.

Automated summary

This Letter reports on the exceptional frequency stability performance of an autonomous cryogenic sapphire oscillator (CSO), with a flicker frequency noise floor below 2 x 10(-16) and a long-term Allan deviation limited by a random walk process of around 1 x 10(-18) root tau, near 1000 seconds. The implementation of advanced instrumentation and ultra-stable frequency references was necessary to achieve this level. This result demonstrates the technological soundness of the CSO technology and sets a competitive upper limit for the ultimate noise floor of cryogenic microwave resonators comparable to ultra-stable optical Fabry-Perot cavities.