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Quantum Measurement Division

The mission of the Quantum Measurement Division is to provide the foundation for the International System of Units (SI), test its limitations, and develop the measurement infrastructure to disseminate SI units related to electrical and mechanical properties. The Quantum Measurement Division covers a wide breadth of interests, including fundamental science and everyday needs and applications. The division’s strategic goals are to explore fundamental aspects of the quantum nature of light and matter; develop quantum metrology and the Quantum SI; create the foundations for electrical, mass, and force metrology from first principles; deliver improved measurement services; and disseminate critically evaluated atomic reference data.

The division is organized into the following six groups: the Atomic Spectroscopy Group; Quantum Optics Group; Laser Cooling and Trapping (LCT) Group; Fundamental Electric Measurements Group; Applied Electrical Metrology Group; and Mass and Force Group. Many staff from the Quantum Optics Group and all staff from the Laser Cooling and Trapping Group are participants in the Joint Quantum Institute (JQI) and the Joint Center for Quantum Information and Computer Science (QuICS), both located on the University of Maryland campus. All of the groups, except the Fundamental Constants/CODATA (Committee on Data for Science and Technology) Center group, were reviewed by the panel.

TECHNICAL QUALITY OF THE WORK

The accomplishments of the division’s groups are many and significant.

The work of the Atomic Spectroscopy Group’s experimental team includes the spectroscopy of highly charged ions and high-resolution precision spectroscopy of atomic lines. Among the group’s accomplishments are applications of newly developed calorimetric sensors recently developed by PML’s Quantum Electrodynamics Division that offer ultrawide bandwidth at an excellent resolution similar to crystal spectrometers. The Atomic Spectroscopy Group collaborates actively and effectively with several university groups.

The Quantum Optics Group addresses a wide variety of topics. On the applied side, these include single-photon detectors with improved time resolution, integrated single-photon sources on a chip, and studies of biophotonics at the single-photon level. On the fundamental side, the Quantum Optics Group studies important questions such as quantum metrology beyond the classical limits and possible implementations of secure quantum communication in a future quantum network. The group is undertaking a significant theoretical effort toward understanding fundamental aspects of entanglement propagation in many-body systems, in particular in systems with long-range interactions. Other noteworthy theoretical work includes quantum-enabled novel detectors for searching for the elusive dark matter and new physics beyond the Standard Model. Staff from this group also contributed significantly to the Quantum Economic Development Consortium (QED-C), which seeks to align research in the quantum field with industry needs.

The Laser Cooling and Trapping Group works on fundamental research at the intersection of atomic, molecular, and optical physics, condense-matter physics, and quantum information science. A unifying theme across these different subfields is the study of coherent quantum phenomena. The research

programs are driven by the need to understand quantum physics in the context of information science and the importance of developing approaches to exploit quantum physics for new technologies. The scientific work of this group is well aligned with the National Quantum Initiative Act, and the research outcomes are important to the broader quantum ecosystem across the world.

The LCT Group’s research portfolio is wide-ranging and includes some of the best programs in the world on ultracold atom physics and quantum many-particle physics. Ultracold atoms, created via laser cooling and trapping, provide a powerful platform for quantum simulation. Quantum simulation is one of the central applications of quantum information science and involves tuning one quantum system to behave like another. This group has pioneered methods to study new and exotic many-particle quantum states relevant to solids using optical-lattice quantum simulators. The work on topological order has spawned new research programs around the world and driven the field forward. The LCT Group is also at the forefront of new technical developments, including sub-wavelength microscopy in optical lattices and applying modern machine learning to optimize the experiments and analyze data. The methods are extremely useful to others in the field. Group members have also pioneered the development of approaches to create superfluid circuits and analogues of the expansion of the early universe using laser-cooled, ultracold atomic gases.

The LCT Group also studies quantum optics and produces some of the best results in this area in the world. Quantum optics is important to creating new devices. A key accomplishment is the demonstration of a high-fidelity, narrow-band photon source and demonstrating interference from photons produced using different species of laser-cooled atoms. This hybridization of two types of atoms and photons at different wavelengths could provide an important platform for devices needed to develop and deploy quantum networks. This group is also at the frontier of nonlinear optics and has produced important results on using atomic systems to produce correlated states of light. These quantum states can be used to improve interferometric measurements.

The LCT Group has a strong theory component that supports activities around the world and the development of new metrology instruments. Key contributions include atomic-structure calculations, which are needed at the frontier of laser cooling and trapping research and are critical to the development of next-generation, optical-lattice clock standards. The group also computes collision properties of atoms and molecules that are critical for the cold-atom vacuum sensor, which is a unique project to provide an absolute standard for ultra-high vacuum pressures. The work of the LCT Group is well aligned with the National Quantum Initiative Act and positions the team to capitalize on opportunities for scientific collaboration with, for example, The National Science Foundation‘s (NSF’s) Quantum Leap Challenge Institutes and the Department of Energy’s (DOE’s) National Quantum Initiative Centers.

The Fundamental Electrical Measurements Group provides the foundation of the nation’s electrical infrastructure through measurement services in the general areas of resistance, impedance, and related quantities. As part of its mission, the group maintains an active research program in precision measurements based on fundamental constants and in the development of quantum electrical standards. The group’s laboratory program is competitive with other top-level, similarly focused national measurement institute (NMI) groups worldwide. Among the most notable achievements, the group had a significant role in the redefinition of the kilogram, leading to the official redefinition of the SI on May 20, 2019. Part of this contribution came in the form of the internally developed Kibble balance, which brought together many disciplines inside the PML to measure the Planck constant to an astonishing accuracy.

Another major innovation, the transition from a GaAs to a graphene implementation of the Quantum Hall Resistance Standard (QHR) has resulted in superior performance, a smaller footprint, and lower build cost. This has enabled industry partners to commercialize these types of instruments. As a necessary step in building the graphene QHR, the group developed and optimized in-house graphene production. This helps further support commercialization of the QHR. A measurement traceability link from the QHR to the Calculable Capacitor has been established, adding additional confidence to the evaluated performance of both measurement standards.

The Applied Electrical Metrology Group supports the nation’s infrastructure by providing calibration services in the general areas of AC and DC voltage, current, phase, and power. As part of this mission, the group maintains an active research program in precision measurement systems based on quantum voltage standards to support calibration services within the group.

The Applied Electrical Metrology Group is competitive with similar groups at other top-level NMIs. The group has advanced the performance of electrical standards beyond any peers within the field. The Group utilizes a Josephson-junction based arbitrary waveform synthesizer (JAWS), developed by PML’s Quantum Electrodynamics Division, that continues to increase output range while lowering costs and physical footprint. New thermal voltage converters have been developed and added to the Standard Reference Instrument (SRI) catalog. Research has started on a new nano-photonic thermal converter that may lead to a self-calibrating device with a zero-traceability calibration chain. Development of a metrology-grade radiofrequency (RF) buffer amplifier could lead to greater accuracy in AC current and RF measurement areas.

With the new definition of the kilogram and the realization of its consensus value, the Mass and Force Group is faced with a number of new challenges. The application of the new kilogram, its realization and dissemination, involves a number of steps ranging from the realization of a high-precision mass comparator, the calibration of standards in vacuum, the transfer from vacuum to air, the establishment of working standards under atmospheric pressure, and the dissemination of mass scales. Noteworthy are a rolling vacuum system designed to transfer weights in high vacuum between stations, and a unique magnetic suspension mass comparator that is essential for the transfer of mass realizations from their vacuum environment to air, with a demonstrated standard uncertainty of 15 micrograms.

The Mass and Force Group also develops an electrostatic force balance that provides a link between milligram-scale masses and the Planck constant. This approach is superior to the alternative of determining small masses by comparing them directly to the kilogram, in which case the associated subdivision of mass process results in accrued uncertainty. The electrostatic force balance approach promises orders-of-magnitude reduction in the uncertainty of masses at the microgram level and could possibly be miniaturized for implementation in a NIST-on-a-chip (NOAC) device.

The photon momentum yields a fundamental relation between mass, force, and laser power that can be used for laser power metrology and force measurements. A miniaturized version of this system using calibrated weights could provide a self-contained NOAC force reference for femtonewton resolution. Small-mass and small-force metrology, in particular in connection with NIST-on-a-chip, offers considerable potential for synergy and cross-fertilization, also with groups with related interest at NIST-Boulder.

TECHNICAL EXPERTISE OF THE STAFF

All the groups have the scientific and engineering staff with the appropriate level of expertise to deliver on their mission. In particular, the technical expertise of the staff in the Quantum Measurement Division is outstanding. The Quantum Optics and LCT Groups are among the best in the world, and their research is at the worldwide forefront of the field. The nearly equal mix of researchers in theory and experiment in the LCT Group is a unique strength that drives the research forward.

The quality of the staff has been recognized by a number of prestigious awards. Recent recipients of federal awards include eight awardees of Gold Medals and three awardees of Bronze Medals of the U.S. Department of Commerce, one recipient of a Presidential Early Career Award, and a Presidential Rank Award. External awards include an Arthur S. Flemming Award and an Arthur S. Flemming/Katherine B. Gebbie Lifetime Achievement Award; a George Snow Award; an International Union of Pure and Applied Physics Young Scientist Prize in Atomic, Molecular, and Optical Physics; and a Clarivate Analytics recognition for highly cited researcher.

ADEQUACY OF RESOURCES

The Quantum Optics and LCT Groups have the appropriate level of scientific expertise to deliver on their mission. A strength of the Quantum Optics and LCT Groups is their integration with the JQI, which includes 15 NIST principal investigators (PIs) out of 32 research staff, with about 40 graduate students working with NIST JQI Fellows. This association enables the NIST researchers to have easier access to students on the University of Maryland campus. The JQI also brings together researchers from different subdisciplines, which has led to new and productive directions for the laser cooling and trapping program. With their wide-ranging interests, they are well-positioned to take advantage of collaborations and new funding opportunities in the field. This is particularly easy for NIST researchers who also have adjoint faculty status at the University of Maryland through JQI.

On the flip side, a substantial part of the research effort of the Quantum Optics and LCT Groups has migrated to the University of Maryland campus, and the resulting geographical separation from NIST can lead to isolation. This issue is mitigated by former students and postdoctoral researchers who become permanent NIST employees and drive collaboration. Lessons learned from the COVID-19 pandemic about remote work have also been beneficial in addressing this issue.

On the financial side, The JQI was supported for 10 years as a NSF Physics Frontier Center. The program was not renewed. This loss provides a challenge to financially supporting the research effort, although the loss of NSF Physics Frontier Center funding is an opportunity to explore new research directions. The LCT Group is highly aligned with the National Quantum Initiative Act and well positioned to capitalize on new federal funding programs in this area.

The JQI research facilities on the University of Maryland campus are among the best in the world but are at physical capacity. Expansion space is needed for the research programs to grow and remain at the frontier. The facilities at the NIST Gaithersburg site have significant deferred-maintenance issues. A recent air-handling failure significantly disrupted research progress.

The Fundamental Electrical Measurements Group has the facilities, equipment, and human resources to support the stated objectives of the organization’s technical program. However, because of the COVID-19 pandemic and the resulting closures and limited physical capacities, the facilities’ malfunctioning HVAC systems have been a source of issues that are blocking progress.

The Applied Electrical Metrology Group has the facilities and equipment to support the stated objectives of the organization’s technical program. However, it suffers from a shortage of available human resources to support the group’s calibration services. Some of the less central activities appear to be understaffed. The flood damage to the Kibble balance laboratory is problematic.

The Atomic Spectroscopy Group is somewhat understaffed, considering the scope, importance, and broad application of its task serving a wide variety of stakeholders from industry, with applications in fundamental science. Critical issues include difficulties hiring, given the small numbers of students trained in spectroscopy at universities, and knowledge transfer when experienced staff retire. There is also a shortage of available human-resource support for the group’s calibration services, on which DOE, the Department of Defense (DoD), NASA, and the commercial industry rely heavily The Group does not have sufficient resources to meet demand for multijunction thermal converters (ac/dc voltage converters).

A hiring challenge is that there is no broad university training for metrologists, who need to understand basic science and engineering. Few universities offer this kind of training. The alternative solution of working with short-time visitors does not help with maintenance continuity and corporate memory.

The excellence and worldwide reputation of a number of staff members of the Quantum Measurement Division result in significant recruitment efforts and attractive job offers by top universities and research institutes. It speaks highly for NIST that it has been largely successful in countering these offers and retaining these superstar researchers.

EFFECTIVENESS OF DISSEMINATION OF OUTPUTS

The Atomic Spectroscopy Group generates, critically evaluates, maintains, and distributes atomic spectroscopy data. It serves a broad community that includes astronomy, chemistry, and extreme ultraviolet (EUV) lithography. The NIST Atomic Database is unique in the world in that it enables a critical evaluation of published data to compile a database.

The Quantum Optics and LCT Groups disseminate products via publication in peer-reviewed journals and at scientific conferences. The publication rate is strong, and results appear in top journals with high impact factor. Many of the publications are frequently cited in the field, which demonstrates the importance of the fundamental and applied research performed at NIST. The LCT Group also plays an important role in collating data on precision measurements to improve knowledge of the fundamental constants of nature and on quantum neutron interferometry at the NIST Center for Neutron Research (NCNR).

The Fundamental Electrical Measurements Group has outputs in the form of publications in peer-reviewed journals and at scientific conferences, and in-house manufactured standards in the form of resistors, scaling resistors, and intrinsic QHR systems. Although still costly, the recent development of graphene-based QHRs has halved the cost of the previous GaAs-based version. The operation cost will also be reduced due to using a closed-loop cryostat that replaces the need of buying liquid helium, a limited resource. Overall, this group serves as an excellent example of balancing the need to research and develop the latest technologies with working with industry to produce practical, cost efficient, standards.

The Applied Electrical Metrology Group has also developed many robust standards that are sold to government and commercial customers through the SRI program. The Group serves as an excellent example of turning research into actual, practical, useful technology that benefits industry. However, success at offering a state-of-the-art standard at a price below similar commercially available standards has pushed demand beyond what the group can supply. Other outputs of the Applied Electrical Metrology Group include publications in peer-reviewed journals and at scientific conferences.

The Mass and Force Group disseminates its results in the form of publications in peer-reviewed journals and at scientific conferences and in-house development and measurement of standards. The group also represents U.S. interests in national and international metrology communities through participation in and leadership of consultative committees, working groups, and standards organizations.

The establishment of the Quantum SI, and in particular the introduction of the new mass standard in terms of Planck’s constant, was accompanied by an outstanding range of outreach and educational activities, including in particular the NIST do-it-yourself LEGO® Kibble balance, which permit a broad audience of students and science enthusiasts to build their own working Kibble balances out of LEGO® bricks. Noteworthy also are the superb lectures by Nobel Laureate W.D. Phillips explaining the Quantum SI revolution to broad audiences worldwide.

GENERAL CONCLUSIONS AND RECOMMENDATIONS

The activities of the Quantum Measurement Division cover a remarkably wide range of topics, including basic research on the foundations of quantum measurements and quantum information science, and their applications to the redefinition and Mise en Pratique of the Quantum SI. The division provides critically evaluated spectroscopic data important for broad areas of science and technology and conducts fundamental and applied research toward the development of electric standards. Division staff is highly qualified. It compares favorably with the best groups worldwide working on related areas, and in a number of activities it is truly world leading. Generally, the division effectively disseminates the results of its work; the Applied Electrical Metrology Group could improve the transfer to industry partners of the technology it develops.

The most significant highlight of the Quantum Measurement Division is its key role in an achievement of historical importance, namely, the establishment of a revised SI unit in 2018. Central to

this paradigm shift away from a mass artefact was the development of a Kibble balance that exploits fundamental electrical metrology: the quantum voltage characteristic of the Josephson effect and the von Klitzing resistance characteristic of the quantum Hall effect. In this way, the Kibble balance realizes a new definition of the kilogram based solely on fundamental constants. The resulting mass standard replaces the International Prototype of Kilogram, a cylinder of platinum-iridium which had served as the standard unit of mass of the metric system ever since 1899. As a result, all SI units have now been put on a fundamental, prototype-free footing and are now defined by giving exact numerical values to seven fundamental constants: the speed of light, the hyperfine transition frequency of Cesium atoms, the Planck constant, the electron charge, the Boltzmann constant, the Avogadro number, and the luminous efficacy. This development is having a profound impact on many of the programs of the Quantum Measurement Division of NIST. In particular, the Mise en Pratique and distribution of the new mass standard requires a number of novel steps that are currently being successfully developed by the group.

The division played a pivotal role in the establishment of the National Quantum Initiative Act and the Quantum Economic Development Consortium. In terms of measurement devices and standards, noteworthy is the development of the new graphene-based quantum Hall standard that operates at higher temperatures and smaller magnetic fields than the GaAs standard. Regarding new quantum technologies, significant achievements have been the development of an integrated single-photon source with a rate of 20 million photons per second; the development of a quantized arbitrary waveform synthesizer that can produce fundamentally accurate signals; and the generation, critical evaluation, and maintenance of an essential and widely used atomic spectroscopic database.

Aging facilities are suffering from delayed maintenance or urgent maintenance interrupted by the COVID-19 pandemic.

The division is experiencing difficulty in recruiting, especially in areas where universities do not provide a training ideally matched to the division’s needs. Most undergraduate students are not aware of the broad range of science and engineering opportunities at NIST. Graduate students are not generally aware of the research opportunities and permanent positions that NIST offers. Attending campus recruiting events, giving seminars within university departments, and connecting with the Quantum Leap Challenge Institutes, DOE National Quantum Initiative centers, and other center-scale programs could provide a pathway to higher visibility

No plan was presented to the panel for improving the NIST Calibration Services, which is a unique service that NIST provides to industry. NIST is the sole provider of calibrations that are directly compared to U.S. national standards, and the service has been stagnant with diminishing quality over the last decade. Division staff attribute this to external budget cuts and loss of support personnel.