On April 4, 2018, Prof. David Howe, IEEE Fellow, from National Institute of Standard and Technology (NIST) paid a visit to SIOM and delivered a presentation entitled “Phase Stability in Next-Generation Atomic Frequency Standards”. Chaired by Prof. LIU Liang, this presentation was warmly welcomed by young researchers and graduate students. 
    Atomic clocks form the basis of everyday timekeeping standard. Separated, hi-accuracy clocks can maintain nanosecond-level autonomous synchronization for many days. The world’s best Cs time standards are atomic fountains that use convenient RF quantum transition at 9,192,631,770 Hz and reach total frequency uncertainties of 2.7 – 4 × 10-16 with many days of averaging time. A new class of optical atomic standards with quantum transitions having +1 × 10-15 uncertainty drives an optical frequency-comb divider (OFD), thus providing exceptional phase stability, or ultra-low phase noise (ULPN), at convenient RF frequencies. This talk focused on how the combination of high atomic accuracy and low-phase noise coupled with reduced size, weight, and power usage pushes certain limits of physics to unlock a new paradigm – creating networks of separated oscillators that maintain extended phase coherence, or a virtual lock, with no means of synchronization except at the start. This single property elevates their usage to a vast array of applications, extending far beyond everyday timekeeping. 
    David A. Howe is senior research advisor to the Time and Frequency Division of the National Institute of Standards and Technology (NIST) and Colorado University Physics Department, Boulder, CO. He is an IEEE Fellow and has over 160 publications and three patents in subjects related to precise frequency and phase-noise standards, timing, and synchronization. His expertise includes time-series analysis, automated accuracy evaluation of primary cesium standards, reduction of oscillator acceleration sensitivity, and precision spectral analysis. He worked with David Wineland from 1973 to 1987 doing advanced research on NIST’s primary cesium standard and compact hydrogen and ammonia standards. He developed and built the first operating compact hydrogen masers in 1979, led and implemented global high-accuracy satellite-based time-synchronization among national laboratories in the maintenance of Universal Coordinated Time (UTC). He won a NIST Bronze Medal and a second Bronze in 2012 for Achievements in Time and Frequency Metrology. He received the 2013 IEEE Cady Award and was co-recipient of the 2013 IEEE UFFC Outstanding Paper and 2015 NIST Astin Measurement Sciences awards.