David Howe

NIST (National Inst. of Standards and Technology
Boulder, CO  80305, USA
E-mail:

January 1, 2017 through June 30, 2018
“Phase Stability in Next-generation Atomic Frequency Standards”

See Abstract
See Biography

  • April 4, 2018, Lecture for Shanghai Institute of Optics and Fine Mechanics (SIOM), Shanghai, China

    http://english.siom.cas.cn/ic/icn/201804/t20180412_191638.html

    The Shanghai Institute of Optics and Fine Mechanics (SIOM), located in Shanghai, develops some of the most advanced reference atomic standards. Its list of projects is impressive, one of the most notable being the first to orbit a cold-atom Cs primary standard in space on the Tiangong-2 space station. Launched and turned on September 15, 2016, it is still successfully running, providing extremely useful data about the operation and evaluation of a primary standard in space with state-0f-the-art accuracy.SIOM is part of the Chinese Academy of Science focused on high-accuracy, ultra-low noise atomic reference oscillators for many services and applications. I was graciously hosted by LIU Liang and LI Lin and greeted by the Deputy Director in the well-attended, stately conference room. The interest in my lecture shifted to the world-record results of 4E(-17) at 1 second frequency stability from Jun Ye’s lab at the University of Colorado. The SIOM scientists are faced with the most advanced lab’s problem of building a narrow-linewidth optical local oscillator for interrogating narrow quantum transitions. The attendees were most interest in the proper measurement of phase noise in the optical domain, general relativity effects of Si optical (mechanical) cavities and how to measure, long-term drift, vibration-sensitivity effects, and prospects for small size, weight, and power.SIOM is actively making progress on developing next-generation atomic standards in space and compact optical clocks. They are obtaining excellent frequency stability below 1E(-15) flicker FM from a compact pulsed optical clock (POP).

  • March 31, 2018, Lecture for National Time Service Centre (NTSC), Xi’an, China

    Xi’an is the location for the National Time Service Centre of PRC. I was hosted by Shuhong Zhao, the Director, and her husband Shongdang, who works in the Radio Astronomy division in the same facility and housing. The time center does leading work in maintaining and providing UTC coordination by means of a stellar group of scientists and one of the largest, diverse sets of atomic clocks. Environmental control and emergency power are among the several priorities for the service.My talk focused on developments in time scale algorithms, particularly Kalman techniques for prediction and control. I also talked about some aspects of the conversion from the current Cs-based definition of the SI second to a Sr-based definition, given the speed with which systematics can now be determined using the lattice clock.NTSC rivals the leading contributors to UTC through primarily scheduled two-way satellite time transfer to PTB, Germany. It maintains free-running time stability below 10 ns at the longest sample times of many months with calibrations to its Cs primary laboratory standard. The time service has built an outstanding facility with environmental-stabilized environments for over two dozen Cs and H atomic reference standards and an extensive, high-resolution multichannel measurement system.Among the notable observations, the NTSC administration and scientists have a commitment to educating and involving youngsters in school about the history, importance, and future prospects of accurate time keeping. One of the best displays and tours of time keeping is provided by NTSC on its campus.
  • March 29, 2018, Lecture for Korea Research Institute of Standards and Science (KRISS), Daejeon, South Korea

    KRISS is the National Measurement Institute of S Korea. A particular focus of the institute is two-way satellite time transfer (TWSTT) to NICT, Japan. The goal is to compare the frequency of lattice clocks at each site at a level consistent with the reported accuracies while reducing the GEO satellite-transponder bandwidth. A new set of waveforms for TWSTT are being investigated that are non-standard (standard being the Satre DSSS waveform originally by Prof. Hartl). Japan (NICT) has developed what amount to a new TWSTT modem which KRISS is using that is suitable for comparisons of Sr and Yb lattice atomic clocks. These atomic clocks are regarded as exhibiting very low phase noise and are contenders for primary standards in future definition of the SI second and realization UTC(KRISS). The new waveforms are generated by a small approximately 10x10x3 cm software-defined interface to the up-down converters used for the Ku-band transceivers and dishes. Frequency comparisons have been reported at the 10-16 level. These data are some of the best TWSTT comparisons between KRISS and NICT labs. KRISS also has a remarkably broad range of standards research including primary frequency standards and maintenance of UTC(KRISS). My talk was well-received with the KRISS audience and, as mentioned, particularly focused on two-way satellite time transfer (TWSTT).

  • January 12, 2018, Lecture for mechanical engineering faculty and students, University of California Irvine, CA

    My lecture focused on how highly phase stable, miniature atomic oscillators can improve indoor localization and remove drift in personal inertial measurement units (IMU). Approximately 100 faculty, students, and staff attended the University of California Irvine at the main auditorium of the MSEM center. UC Irvine has one of the best programs to design, fabricate, and test micro-scale inertial-sensor components. Several professors work with grad students in the university’s laboratory and fabrication facility to develop smaller and better-performing personal IMUs. The use of phase stable oscillators for a method of detection of IMU errors received great interest. A large source of funding is from Public Safety Communications Research (PSCR) to aid first responders. Dr. Zak Kassas and his team and I plan to follow up on ways to further their approach using signals of opportunity (SOPs) in (1) indoor localization and (2) augmenting GPS. Their best results are achieved using the carrier phase from cellular CDMA signals in an urban environment. A video is shown at the ASPIN Labs website at http://aspin.ucr.edu/videos.html. Multipath in rural, urban-canyon, and emergency environments prevent sufficient indoor localization. I explained how phase stable local oscillators are a great technical resource as they provide a way to detect and correct multipath.

  • December 18-19, 2017, Series of Lectures for National Institute of Standards, Cairo, EG

    The National Institute of Standards in Cairo maintains a small but effective calibration service. The primary audience at NIS consisted of grad students and Dr. Gihan Gomah, the head of the Time and Frequency Lab of NIS. Other managers and students attended from the laser, RF-microwave, and power calibration services. I presented two days of talks that were requested by NIS on the following specific subjects:

    • The use, design, and advantages of Kalman filters in time scale algorithms,
    • Principles and practices used in Cs-beam and H-maser atomic clocks,
    • Construction of an FPGA-based GNSS (GPS) receiver,
    • Optimizing GNSS (GPS) tracking-loop and architecture for GPS time/frequency acquisition.

    The students are quite capable and I offered my advice on new, relevant topics in research, particularly on algorithms, that would be novel and publishable and would be relevant to the maintenance of a National Measurement Institute such as NIS. In all, the lectures were very well received with a great deal of attendee interaction.

  • December 11-12, 2017, Plenary Lecture: 3rd International Conference on High Energy Physics, Rome, ITI presented a plenary talk on accurate timing to a rather select audience. https://highenergyphysics.conferenceseries.com/scientific-program

    This was the 3rd conference devoted to applied high energy physics and there were about 20 who attended. The diversity of knowledge among the attendees was remarkable. The title of my IEEE talk was: “Phase Stability in Next-generation Atomic Frequency Standards” and the talk shifted emphasis to three areas of primary interest to this audience. Using measurements of the most advanced lattice clocks worldwide: (1) detecting changes in the fine-structure constant, alpha, that affect quantum-consistency theory, (2) the search for the nuclear ‘clock’ transition in Thorium-229, and (3) position, navigation, and timing in deep space using x-ray pulsar signals in the star field. In particular, the group at Max Planck Inst. who came has projects about nuclear transitions in a general sense. Theoretically there exists a strong XUV transition around 160nm that has yet to be found that has some ideal ‘clock’ stability properties. The measurement of this particular transition is very difficult because Thorium-229 isotope is radioactive and because the line is narrow and at XUV. Also, this audience followed the advances that I presented in accurate atomic clocks. My work directly relates to measurements of atomic clocks at accuracy of 1E(-16) short-term frequency error and less than 1E(-18) long-term.

  • March 29, 2017, Plenary Lecture: IEEE Inertial Sensors and Systems, 2017, Kauai, HI

    This is the 4th Symposium on the subject of inertial sensors sponsored by IEEE.  A key aspect is calibration of these sensors in real time using position, navigation, timing (PNT).  This calibration relies on GPS-GNSS, but GPS is not accurate enough or sometimes is not available for small IMUs and magnetometers capable of below 10 cm precision for over 15 mins after calibration.  Below 10 cm positioning can use ultra-low phase noise atomic oscillators with the sensor, especially indoors, primarily as a means of detecting and correcting GPS multipath, the cause of errors.  This is the 4th Symposium on the subject of inertial sensors sponsored by IEEE.  A key aspect is calibration of these sensors in real time using position, navigation, timing (PNT).  This calibration relies on GPS-GNSS, but GPS is not accurate enough or sometimes is not available for small IMUs and magnetometers capable of below 10 cm precision for over 15 mins after calibration.  Below 10 cm positioning can use ultra-low phase noise atomic oscillators with the sensor, especially indoors, primarily as a means of detecting and correcting GPS multipath, the cause of errors.
    I also talked on a similar strategy for accurate IMU calibration by using beacons within an LTE Network and an app on a smartphone. The lecture entitled, “Advanced Positioning PNT within an LTE Network” had over 160 people attended.  I represented IEEE, and the IEEE Sensors Council provided support.