Atomic clocks are an important part of many potential quantum sensors, in addition to constituting a type of quantum sensor in their own right. For many applications, high-performance clocks must be realized in a manner compatible with operation outside of a laboratory. In this talk, I will outline efforts at developing the integrated photonics technology needed to miniaturize optical atomic clocks, including our lab’s own efforts on nonlinear nanophotonics components. I will also discuss how such integrated photonics can also impact the development of other types of quantum sensors, and present some of the challenges involved in advancing these technologies.
Optical atomic clocks have many applications in the definition of the time and the length, measurement of fundamental constants and their potential variations with time, testing of relativity, very long baseline interferometry, geodesy, and global navigation satellite systems. An optical clock consists of three parts: ultra-stable laser, frequency comb and trapped ions or atoms. The accuracy of optical atomic clocks can be affected by Doppler shift, Zeeman shift, Stark shift, collision shift, blackbody radiation (BBR) shift, etc. The BBR shift is very difficult to be characterized and controlled. Among all optical atomic clocks under current development, Al
+ optical clock has the smallest BBR shift at a level of
4.0×10−19, therefore the Al
+ is a promising ion for high-accuracy optical frequency standard. In this article we give a review on the three parts of optical frequency standards, the basic working principle of Al
+ ion optical frequency standard based on quantum logic technique, and research progress of an Al
+ optical clock under development at Huazhong University of Science and Technology.
Optical atomic clocks produce highly stable frequency standards and frequency combs bridge clock frequencies with hundreds of terahertz difference. In this paper, we propose a hybrid clock scheme, where a light source pumps an active optical clock through a microresonator-based nonlinear third harmonic process, serves as a passive optical clock via indirectly locking its frequency to an atomic transition, and drives a chip-scale microcomb whose mode spacing is stabilized using the active optical clock. The operation of the whole hybrid system is investigated through simulation analysis. The numerical results show: (i) The short-term frequency stability of the passive optical clock follows an Allan deviation of σ y ( τ ) = 9.3 × 10 −14 τ −1/2 with the averaging time τ , limited by the population fluctuations of interrogated atoms. (ii) The frequency stability of the active optical clock reaches σ y ( τ ) = 6.2 × 10 −15 τ −1/2 , which is close to the quantum noise limit. (iii) The mode spacing of the stabilized microcomb has a shot-noise-limited Allan deviation of σ y ( τ ) = 1.9 × 10 −11 τ −1/2 . Our hybrid scheme may be realized using recently developed technologies in (micro)photonics and atomic physics, paving the way towards on-chip optical frequency comparison, synthesis, and synchronization.