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Time and Frequency Division

Accurate time and frequency services are vital for U.S. critical infrastructure and long-term U.S. economic growth and global leadership. The Physical Measurement Laboratory’s (PML’s) Time and Frequency Division has a clear mission to “develop and distribute the highest accuracy time and frequency measurements and related technologies to support commerce, research, national priorities, and the public.” The division’s activities fall into three primary areas: (1) accurately and precisely realizing official U.S. time and frequency, (2) operating a wide range of measurement services to distribute time and frequency and related quantities, and (3) performing basic research and developing technology to improve time and frequency standards and related technologies. An important feature of scientific and technical work in the division is collaboration across multiple groups to achieve results and produce scientific products.

The Time and Frequency Division is in Boulder, Colorado, with some staff located in Fort Collins, Colorado, and Kauai, Hawaii. The division has 137 staff, including 7 in administrative support, 38 NIST scientists, and 92 associates. The division consists of seven groups: (1) Ion Storage, (2) Phase Noise Metrology, (3) Time Realization and Distribution, (4) Quantum and Nonlinear Nanophotonics, (5) Precision Photonic Synthesis, (6) Neutral Atom Optical Clocks, and (7) Atomic Devices and Instrumentation. The fiscal year 2023 division budget is $27.9 million, of which almost $18 million is scientific and technical research and services, with 33 percent of those services being sourced outside of the National Institute of Standards and Technology (NIST).

The Time and Frequency Division is continuing its long history of excelling in its mission. The quality and impact of the research being produced is vital to the continued leadership of NIST in this arena, both nationally and internationally. Additionally, the division is providing critical operational services for multiple stakeholders including U.S. commerce, defense, industry, and the general public. Notably, the division has played a leading role in ushering in quantum computing and quantum technology. Significant services and research results have been identified along with some targeted areas that could be strengthened and improved for the continued excellence and leadership of the division into the future.

ASSESSMENT OF TECHNICAL PROGRAMS

The overall collection of scientific and technical work being carried out in the Time and Frequency Division in the NIST PML is of the highest quality. This is exemplified by the wide range of areas where the division leads the world in the development of novel scientific techniques to advance time and frequency measurements and related technologies. The quality and quantity of high-impact publications generated by the division is exceptional, including 16 papers published in Nature and Science and 30 papers published in Physical Review Letters over the past 5 years. Some scientific highlights include:

• The world-leading accuracy of the aluminum ion clocks in the Ion Storage Group and the world-leading precision of the ytterbium (Yb) lattice clocks in the Neutral Atom Optical Clocks Group as well as the development of a portable Yb optical lattice clock as a new tool for high-precision optical clock comparisons.

• World-leading frequency ratio values were obtained between the Al+ and Yb optical clocks at NIST and the strontium (Sr) optical clock at JILA. The measurements involved several groups in the Time and Frequency Division combining their efforts. The results have provided an important step toward the redefinition of the second in the International System of Units (SI) as well as placing new constraints on the nature of dark matter.
• The pioneering techniques originally developed in the Ion Storage Group have given rise to an entirely new industry of quantum computing. The group continues to remain at the forefront of innovation, with recent progress in areas such as microwave gates, multi-species techniques, molecular ions, and new ion trap designs that are supporting industry efforts and also opening new directions in the field.

The Time and Frequency Division also provides a number of unique and critical technical services to stakeholders in the private and public sectors. These include:

• The Time Realization and Distribution Group generates NIST’s realization of Coordinated Universal Time, called UTC(NIST). UTC(NIST) is well recognized globally for its stability and is disseminated via multiple techniques, including the widely used NIST Internet Time Service, remote calibration services based on the Global Navigation Satellite System common view, radio broadcasts, and now via two new services, Time over Fiber and Time over Satellite.
• The Phase Noise Metrology Group provides valuable microwave phase noise calibration and measurement services to industry and the Department of Defense.

The division is also world-leading in the development of cutting-edge time- and frequency-related technologies with higher technology readiness levels that are industry and application oriented and are also relevant to other scientific disciplines:

• The Atomic Devices and Instrumentation Group vigorously innovates in the area of compact, low-power quantum sensors and clocks and leads research efforts in the $10 million/year NIST on a Chip program. Among other important efforts, the group is developing a rubidium two-photon optical clock targeted to replace or supplement the hydrogen maser, the current workhorse for realizing UTC across the planet, and yet one that’s harder to acquire and maintain as industry phases such masers out. This group continues to demonstrate close ties to industry and strong levels of technology transfer.
• The Quantum and Nonlinear Nanophotonic Systems Group is developing integrated photonics and making important advances into miniaturized, integrated optical clocks (including subsystems such as microcombs and tunable lasers) that are potentially very important for next-generation time-keeping.
• The Precision Photonic Synthesis Group has demonstrated world-record-setting low-phase noise microwave generation from optical sources and is producing cutting-edge miniaturized ultrastable optical cavities through new fabrication techniques.

The quality of the technical programs makes the Time and Frequency Division well-suited to reach its stated technical objectives. However, there are several opportunities for improvement:

• A national standards institute of this caliber should be operating a cesium (Cs) fountain primary frequency standard to provide regular contributions to the International Bureau of Weights and Measures (BIPM) for inclusion in the computation of UTC. The division is aware of this and has been working to remedy the situation by setting up and characterizing a new Cs fountain (NISTF3), as well as refurbishing an older fountain (NIST-F4). In parallel, the division is also working to develop a robust Sr+ optical ion frequency standard that can serve the same needs, acting as a

• secondary representation of the SI second. The panel encourages the division to prioritize these developments to ensure that NIST can provide measurement results that are traceable to the SI second with the lowest uncertainty and be able to regularly contribute to international time scales.
• There are important opportunities for expanding the phase noise characterization services and capabilities performed by the Phase Noise Metrology groups to higher frequencies (terahertz) and optical phase noise measurements in conjunction with the Precision Photonic Synthesis Group, to keep pace with the development of new and emerging communications and metrology technologies.
• The compact Sr lattice clock project under development in the Quantum and Nonlinear Nanophotonic Systems Group is very promising and represents an important future technology with a wide variety of applications. Currently, the project is externally funded, and the focus is only on some components of a clock. The effort could benefit from additional internal funding to support the development of other aspects, such as the photonic integration of lasers, active optics, and light distribution, which are not covered by the current external support.
• While the time distribution service is currently serving millions of customers and expanding to additional platforms, the staff and infrastructure seem to be operating at maximum capacity with little room for needed growth in this important service. It would be valuable if the architecture and infrastructure of this service were to be evaluated and modernized with an eye toward growth, security, and robustness.

In light of these considerations, the panel offers the following recommendations:

Recommendation 6-1: The Time and Frequency Division should prioritize development of its Cs fountain primary frequency standards, its Sr+ secondary standard, or both to ensure that the National Institute of Standards and Technology can regularly contribute to international time scales. The division should ensure the continuation of its recent progress with the addition of new personnel to these efforts.

Recommendation 6-2: The architecture and infrastructure of the time distribution service should be evaluated and modernized with an emphasis on growth, security, robustness, and adequate staffing of this crucial service for the country.

ASSESSMENT OF SCIENTIFIC EXPERTISE

The Time and Frequency Division has world-leading experts in all seven of its groups. This results in high-impact scientific research and enables the delivery of unique products and services, while also attracting new generations of high-caliber junior scientists; when interviewed, junior scientists in the division expressed their enthusiasm for working with leaders in their field as one of the primary motivations for joining the division. The scientific expertise across the division is further evidenced by the outstanding number of prestigious external prizes and fellowships that have been awarded to staff members.

The group leaders demonstrate deep technical knowledge and enthusiasm for the areas they oversee. The division chief is to be particularly commended for her leadership of the technical direction while also focusing on improving the diversity and representation of the workforce. Based on discussions with staff and the previous report, the division morale, the division community, and the quality of the facilities have all improved under her leadership.

The staff also ensure that NIST has an influential voice in relevant international committees. Of particular note is the strong NIST representation on the Consultative Committee for Time and Frequency and its working groups. Important topics under discussion at the moment include the redefinition of the SI second, the future of leap seconds, and the mutual benefit of UTC and global navigation satellite system.

Decisions made in these committees will have long-term implications for time and frequency needs in the future, so it is important that NIST is able to influence that future direction.

The organization’s technical programs are greatly enhanced by the scientific expertise of the staff members. In fact, the continued success of the division is strongly dependent on its staff and thus it is important to preserve the division’s technical expertise in the long-term. In some cases, there is a large concentration of expertise in a small number of outstanding individuals, making the division vulnerable to a lack of continuity in critical knowledge and services if these individuals depart. Given that, the panel offers the following recommendation:

Recommendation 6-3: The Time and Frequency Division should ensure that succession plans are put in place and that knowledge and responsibilities are shared and distributed among the wider members and teams. The Physical Measurement Laboratory’s new succession funding program is encouraging, but all critical areas should be evaluated to identify and mitigate potential single points of failure.

BUDGET, FACILITIES, EQUIPMENT, AND HUMAN RESOURCES

NIST’s budget for the Time and Frequency Division appears to be sufficient to maintain facilities, equipment, and staff for the existing services and research developments. All of the division group leaders reported strong support from the division chief and are content with their respective current budgets. It was noted by the panel that some of the groups (such as the Phase Noise Metrology Group) depend heavily on external funding (more than 60 percent of their budget is through external funds), which could contribute to issues related to finding and retaining staff because of the uncertainty of yearly budgets. In addition, some staff members expressed concerns that it is gradually becoming more difficult to secure funding for new research directions, due in part to the lengthy process at NIST that often delays the acceptance of funds from other government agencies, such as the Defense Advanced Research Projects Agency. The delay sometimes takes so long that funds cannot be accepted in the fiscal year in which they were targeted for, prompting their withdrawal.

The Time and Frequency Division has a majority of its laboratories located in the Katharine Blodgett Gebbie Laboratory Building 81 and the Radio Building 01 in Boulder. The cutting-edge facilities and equipment located in Building 81 are of very high quality and support both the time-keeping services and fundamental research being conducted in the division and are a direct result of the relatively recent construction (within the past 15 years). The Atomic Devices and Instrumentation and the Time Realization and Distribution groups’ laboratories are still housed partially in Building 01 (Wing 1 and the Spine), which appear to be adequate for current research efforts. However, owing to the nature of renovations and the clear limitation of existing space, many of division staff’s office spaces have heating, ventilation, and air conditioning issues (portable heaters and air conditioners are necessary), are subject to construction noise, have experienced flooding, have issues with pests, and can be located very close to actual construction, causing disturbances to workflows or incurring safety issues. It has also been noted by key staff that once the renovations have been completed, all available laboratory and office space will likely be completely filled, with no room for growth or innovation (this was referenced by one NIST staff scientist as “The renovations will be appropriate for 2010 needs, not 2030 needs”). There was also mention of critical infrastructure (including the sewer) of Building 01 that needs to be addressed for the health and safety of the staff as well as power outages in many of the buildings affecting the research laboratories.

Recommendation 6-4: The Physical Measurement Laboratory should act to improve the critical infrastructure of Building 01 as well as to mitigate power outages in many of the buildings affecting the research laboratories or find other suitable space to house these groups.

Because time keeping is a core function of the Time and Frequency Division, it would be beneficial to have better infrastructure for connecting remote facilities that support time distribution, such as direct links (fiber and free-space) to key U.S. timekeeping facilities including the U.S. Naval Observatory, Fort Collins, and the NIST Gaithersburg campus. Similarly, as noted in Recommendation 6-2, the Time Realization and Distribution Group needs more funding and personnel dedicated to its time services, commensurate with the crucial role these serve for the country.

The human resources in the Time and Frequency Division are of the highest quality for the types of services and research being performed at NIST. This ranges from the staff scientists to postdocs and graduate students. The high quality is demonstrated by both the cutting-edge research and the critical time-keeping services performed in the division. The recent addition of a highly qualified safety officer (who is also a Time and Frequency Division staff scientist) is a very important step toward ensuring that the laboratories and experiments are as safe as possible for the division personnel while also allowing high-quality research to continue. While advances have been made to increase the representation of certain minority demographics (e.g., women under 30 years of age and Latinos) at NIST, the division still has a long way to go to achieve a level of diversity that reflects the current diversity of those receiving PhDs in physics, let alone the society at large. One example of this is that African Americans appear to be dramatically underrepresented in the division. While this is a complex problem, outreach and recruiting at colleges and universities with statistically higher populations of minorities for collaborations, as well as workforce development, may solve this problem. In fact, the division has initiated a new recruiting relationship with a historically black college and expects to have two African American visiting staff members next year; this is a good start.

Despite the excellence the panel found in the staff throughout all of the groups in the Time and Frequency Division, it did find a few main concerns: (1) the ability to find and obtain new and high-quality postdocs and graduate students; (2) the processes associated with hiring permanent staff; (3) a shortage of staff in key service areas; and (4) a shortage of administrative staff to allow the technical staff to focus on technical and scientific responsibilities. Finding and acquiring new staff has been most challenging at the postdoc and graduate student level; this has been attributed to the growth in the quantum computing industry. In some respects, NIST is a victim of its own success in terms of advancing the industry with which it now finds itself competing for personnel. Within the limits of government-set pay schedules and the realities of PML’s staffing and budget situation, offering higher salaries is a possible solution for this problem. Another possible solution, within the same limits, is to increase the opportunities for the conversion of postdocs to permanent staff. For the more service-oriented groups, and if these areas are no longer able to attract a consistent stream of postdocs and graduate students, a few more permanent positions could keep these critical areas flourishing for the nation. Concerning the process associated with hiring permanent staff, it was noted that there can be serious restrictions in adding new positions, including, but not limited to, the federal requirements for posting new positions (which can lead to reduced quality and size of the applicant pool), the internal size of NIST’s Human Resources (HR) Department (which was leading to significant delays in the hiring process but is perhaps somewhat improved now), communication between HR and applicants during the submission process (applicants were not being told if their submissions were inadequate and therefore disqualified), and proper advertisement of these positions (postdocs at NIST currently express frustration about not knowing when new positions were available). Lastly, some of the permanent division staff did admit the amount of administrative duties they are burdened with can affect their ability to conduct their research. Additional administrative personnel would directly improve the staff’s ability to get more research accomplished.

One additional area that PML could improve is to facilitate even more communication among research groups. While individual research groups are run very efficiently to achieve industry-leading research, and junior researchers report excellent mentorship and a respectful environment with easy access to collaborate with experts across the division, postdocs only stay for a few years and are very busy so do not get enough in-depth exposure to their colleagues. Several individuals spoke about the benefit of attending the poster presentation prepared for this panel. In response, the division chief will consider ways to enhance knowledge sharing, such as mini poster sessions during weekly coffee hours or

reinstituting the annual poster session that stopped during the COVID-19 pandemic. It was clear that the expertise and collaborative environment was key in attracting top talent to the postdoc pool, so it is important that everything be done to maintain this.

EFFECTIVENESS OF DISSEMINATION EFFORTS

The Time and Frequency Division has a comprehensive approach for communicating with its stakeholders in all three of the scientific, technological, and service areas related to time and frequency. The scientific output of the division is widely disseminated through publication in top-tier scientific journals and in conferences related to atomic physics and fundamental physics and those specifically catering to the time and frequency community. The division output is also highlighted to the public at large through articles and news releases in the popular press, as appropriate. With regard to the conferences, all staff members (including associates) have the opportunity to attend conferences and present their work. Division staff also actively participate and serve in various committees within the scientific, engineering, and international organizations that relate to the field of time and frequency. In particular, the division has taken an active role in the committee organized by BIPM to transition the definition of the SI second with the advent of new optical clocks. The division also does an excellent job of promoting the accomplishments of its staff members by nominating them for various awards and recognitions, within both NIST and the Department of Commerce and also through national and international professional organizations.

The Time and Frequency Division is the only organization in the nation that provides an annual seminar on time and frequency to support the industry and others working in the field. This is a valuable enterprise, and currently there are no other educational opportunities that provide the needed training and education in this very specialized field. The two service groups also remain in close contact with the calibration customers and provide information about new capabilities as they are being developed.

The division also produces patents and intellectual property in support of commercialization. There are several instances of either licensing patents to industry or putting them in the public domain, both of which have led to development and commercialization of related products.

In general, the Time and Frequency Division does an excellent job of disseminating information to the stakeholders. However, the impact of the division’s efforts could be further amplified through improved outreach to industry. There are several examples of techniques and instrumentations, in addition to patents and intellectual property, that the division has developed, such as the new phase noise measurement instrumentation based on a field-programmable gate array, that are mostly disclosed through conference papers. Members of industry may not regularly attend academic or technical conferences, so access to that type of information is limited for them, which reduces the number of stakeholders who could benefit from these new developments. It would be helpful if such information was made available through the website or notices sent via email (e.g., subscription mailing lists) to notify industry. Monitoring traffic to these website areas and subscriber lists would also add to the numerous ways the division already employs to measure stakeholder impact, such as tallying 100 billion network time protocol requests per day, more than 60 subscribers to Time and Frequency Measurement and Analysis Services, and the division’s numerous publications, citations, publication journals, collaborators, patents, licenses, and disclosures. Despite collecting all these positive impacts, the division would further benefit from doing a better job of illustrating the significant long-term impact of its work and the benefit to the U.S. economy, to U.S. leadership, and to the general public. An example here is the evolution of the quantum computing industry from early research at NIST. This is a valuable national asset that needs to be recognized as such.