Frequency-comb-based digital clockwork for next-generation optical clocks

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This proposal aims to develop optical clockworks, the systems used to read out the time from an optical clock. An optical clock uses a very stable laser, referenced to an isolated atom's or multiple atoms' transition frequency to provide very fine and accurate subdivisions of time. Its precision comes from the very high frequency of oscillation of light compared to usual radio frequency oscillators, but this also makes it difficult to read the clock because the frequency is too high for conventional electronic means. Since these optical clocks already enable better time measurements and are likely to soon replace radio frequency atomic clock in time and frequency standards, it is very important that we develop the basic technology to support them. Measuring time accurately is a fundamental process, required for a wide range of applications, from answering deep scientific questions about our physical world (searching for gravitational waves, mapping gravity field distortions from the Earth and planets, testing for possible changes in what we now consider physical constants), to enabling very practical applications of accurate global navigation, high efficiency communications systems and many more. Often, the limit to the precision of these scientific and technological endeavours is linked to the performance of its clock. To build a clock, we need a stable, repeatable physical phenomenon (here, the oscillation of the laser electromagnetic field locked to an atomic transition) but also the means to count the number of these oscillations that have occurred. Every optical clock thus requires commensurate optical clockwork to count these oscillations and make the clocks' exquisite accuracy available for applications. Such clockwork is based on a type of laser emitting short pulses called frequency combs. These combs serve as a kind of strobe light for the clock: instead of counting each and every oscillation, combs enable us to very precisely pinpoint one every million oscillations, bringing the counting rate within the range of electronic techniques. Unfortunately these frequency combs are currently not robust and mature enough to operate for long term and outside the controlled environment of the laboratory. This research will use digital signal processing techniques and statistics to analyze, design and control robust frequency comb systems that can operate as reliably and accurately as optical clocks will require in the future.