3
Applied Physics Division

The mission of the Applied Physics Division is to carry out research and develop technologies that will enhance measurement capabilities in such vital areas as national security, advanced manufacturing, strategic computing, quantitative imaging, and quantum communications. Among the strategically important technologies that rely on the laboratory’s state-of-the-art measurement capabilities are photonics, magnetics, and imaging. To fulfill its mission, the division has developed world-class expertise in radiometry, spectroscopy, sensing, quantitative imaging, quantum measurements, and advanced communications, among other areas, with a specific focus on such capabilities as optical power measurements, quantum information, magnetic imaging, terahertz imaging research, optical frequency combs research, and quantum nanostructure characterization. The division also operates a state-of-the-art precision imaging facility used to characterize devices that are important to advancing measurement science, standards, and services.

The division includes seven individual research groups and more than 105 staff and associates from the United States and around the world, many of whom work on projects in more than one group. The groups are Advanced Microwave Photonics, Faint Photonics, Molecular and BioPhotonics, Quantum Nanophotonics, Magnetic Imaging, Sources and Detectors, and Quantitative Nanostructure Characterization. In addition to the work within and across groups in the division, the workers in the division share their expertise and innovations with colleagues in academia, industry, and other government agencies in order to maximize the value of their research.

ASSESSMENT OF TECHNICAL PROGRAMS

The Applied Physics Division has seven group leaders and spans a variety of disciplines including optical power measurements, quantum information, magnetic imaging, terahertz imaging, and quantitative nanostructure characterization. The division also provides a variety of calibration services including laser power and energy instrument metrology, magnetic resonance imaging (MRI), optical medical imaging, and precision semiconductor nanostructures. Many of these laboratories are sited in newly renovated space, which enables their activities. All of these efforts are remarkably well integrated with each other, and there is synergy between seemingly different projects. This is also true regarding interactions between calibration services and basic science, which superficially would appear to have different objectives. Furthermore, there is substantial enthusiasm for all activities. The success of these programs is evident in metrics such as publications per year, citations per year, external collaborations, press coverage, and awards (discussed in more detail in the Assessment of Scientific Expertise and the Effectiveness of Dissemination Efforts sections, below). The technical programs are clearly highly successful. However, there are opportunities for further development that would build on these successes in the areas of artificial intelligence (AI) expertise, materials characterization capabilities, and broader outreach to major industries. In addition, there are also opportunities to make improvements in the facilities infrastructure, laboratory safety, and onsite human resources support. These items are described in more detail throughout the report. Several examples of the exciting, innovative programs in this division are described below.

Qubits

The Faint Photonics and Quantum Nanophotonics Group carries out a number of synergistic experiments that couple and build on technologies developed in house, including superconducting nanowire single-photon detectors. The nanowire single-photon detectors provide the basis for many of the measurements in associated experiments. As transmon qubits operate in approximately the 5 GHz regime, expertise in microwave quantum optics is critical, and the group within the Applied Physics Division does a superb job in producing high-quality research, publishing in well-respected international journals, and creating overall work that competes with the best in the world. The entangled mechanical resonators are but one example of this exciting work.

The entangled-photon experiment used to achieve loophole-free Bell tests is an example of a core application within the National Institute of Standards and Technology (NIST) charter, where entangled photons are separated by polarization and transmitted through optical fibers to demonstrate the usefulness of such photons in “tamper-resistant” communications. While the periodically poled nonlinear crystals used to down-convert 775 nm photons to two entangled and cross-polarized 1,550 nm photons are also being used in this way in several other laboratories world-wide, the high level of engineering of this experiment at NIST produces a high detection success rate that brings entangled communication closer to actual utility.

Another example of important work being carried out here is the transduction work incorporating a quantum dot interacting with a surface acoustic wave to encode a radio-frequency photon (e.g., produced by a transmon qubit) onto an optical photon appropriate for transmission in an optical fiber. At this stage of development, this somewhat complicated process involving synchronization of signals is challenging. Of great importance will be the demonstration of high conversion rates which will be critical to successful wavefunction transmission between, for example, one dilution refrigerator and another for scaling.

Overall, mastering the interactions among microwave photons and resonators, nanomechanical systems, transduction, and more, all operating at 10 mK to 1 K is critically important in measurement science, and NIST’s contributions are a key component of that research.

MRI (Phantoms and Low Field)

Several activities related to magnetic resonance imaging were discussed, with the highlights including quantitative MRI for medicine, contrast agents, and low-field MRI. Quantitative MRI focuses on the development of phantoms; that is, calibration structures that mimic biological structures of interest. The dissemination of these resources is accomplished through engagement with various institutes and international societies as well as through a lending library. Work on contrast agents focuses on testing existing contrast agents and developing new materials with enhanced functions. Both of these activities are well justified, organized, impactful, and likely to continue to be in demand by medical professionals. Low-field MRI presents a developing opportunity with the potential for rapid growth because of the portability and reduced cost of these instruments. Current areas of activity include developing a low-field system for monitoring of plant root systems and acquisition of a Food and Drug Administration–approved Hyperfine Swoop MRI scanner. If successfully developed, these technologies will present opportunities for commercialization. However, the disadvantage to low-field MRI is that it produces low-resolution images. In order to overcome this, AI is being trained to improve image quality. This is primarily being done through a collaboration with NIST’s Information Technology Laboratory. As described below, the panel is unsure whether this is a sufficiently robust investment of resources in this important problem. AI technologies are advancing at an unprecedented pace, and it may be beneficial to embed AI experts directly in this project or to develop a group in Boulder that is focused on AI which can provide expertise to other projects.

Differential Absorption LIDAR

NIST has undeniably demonstrated an exceptional prowess in remote sensing technology through its groundbreaking work in differential absorption light detection and ranging (LIDAR and Differential absorption LIDAR [DIAL]). NIST’s expertise in this field is evident in its ability to perform standoff measurements of atmospheric trace gases, showcasing its advanced and precise measurement techniques using LIDAR. With such remarkable achievements, NIST’s proficiency in developing and refining DIAL technology is truly commendable.

As the demand for reliable and safe semi-autonomous cars continues to grow, the significance of LIDAR technology as a critical component for environmental perception and hazard detection during driving cannot be overstated. Given NIST’s expertise in DIAL, it is ideally positioned to leverage its knowledge and translate its cutting-edge technology to the development of LIDAR systems for semi-autonomous vehicles.

This translation holds immense promise for enhancing the safety of semi-autonomous vehicles, aiding in the establishment of government regulations, and fostering advances in autonomous driving technology. By applying its DIAL expertise to LIDAR for cars, NIST would contribute to the broader landscape of the automotive industry, fueling innovation and paving the way for the widespread adoption of reliable and efficient semi-autonomous driving systems.

Optoelectronic Hardware for Artificial Intelligence

The Hardware for Artificial Intelligence project (also known as Superconducting Optoelectronic Networks) is a project that combines novel, enabling technologies in single-photon detection with an optical fan-in and fan-out architecture that closely mimics the human brain. The promise is a computing speed greater than that exhibited by cloud super-computers but with only one-fifth the power dissipation. The project is an illustration of how the Applied Physics Division collaborates effectively across boundaries (e.g., the additional application of superconducting nanowire single-photon detectors) and how innovation is encouraged from the bottom up: the project is a recipient of an Innovations in Measurement Science award. Not only is this work likely to garner recognition in the scientific community, but it may also contribute to important commercial applications. The Applied Physics Division has an opportunity to capitalize on this opportunity and accelerate the project from the current “aspirational” objective of 15 years. The team inspired confidence by communicating with passion their logic, plan, and objectives.

ASSESSMENT OF SCIENTIFIC EXPERTISE

In general, the Applied Physics Division staff appear to have excellent scientific knowledge, skills, and innovative talent. They excel in many areas, including optical physics, spectroscopy, superconducting device physics, quantum physics, cryogenics, and fabrication of devices. They are uniformly passionate about the science they are doing and committed to the mission of NIST. They display good teamwork as well as the ability to work across boundaries. There is considerable synergy among a broad array of programs. Division scientists have been the recipients of notable awards and recognitions, highlighting the exceptional quality and impact of their scientific contributions. These awards include Gold, Silver, and Bronze Awards internal to NIST, as well as fellowships from membership organizations such as the Institute of Electrical and Electronics Engineers, the American Physical Society, and Optica, and several Presidential Early Career Awards for Scientists and Engineers (PECASE). These accolades serve as a testament to the expertise of division’s staff and the value they bring to their field.

A very fruitful meeting with early career scientists was held. At least one scientist expressed frustration that there seemed to be no opportunities for career positions or advancement, a comment which suggests that NIST is not viewed as a desirable place to work. There were, however, two scientists

among the group of seven who had recently advanced to permanent positions. Among this group every one of them seemed to be very pleased with the mentoring they were receiving from their advisors and supervisors. Mentoring is critically important for the scientific and career growth of young scientists, and it appears that mentoring in the Applied Physics Division is of high quality.

Applications of Artificial Intelligence

There appear to be several projects that would benefit from more robust support by experts in AI within the Applied Physics Division, in order to develop an organized AI strategy. Prominent examples of work that could use such support are activities that produce low-resolution images (and possibly even higher-resolution images). This includes low-field MRI, terahertz imaging, and hyperspectral imaging for tumor margin analysis, although there are probably other areas in addition that are well suited. An interesting example is seen for terahertz spectroscopy when it is implemented to nondestructively image the internal structure of bridge decks. This is accomplished by locally heating steel-reinforced concrete and then observing the magnetic phase transition of hematite, which is produced as steel ages. This is a novel application that relies on low-resolution terahertz images that are subsequently improved by AI. If this technology could be deployed, it would have great value for assessing aging infrastructure throughout the nation and would be likely to find other applications in industry. Current AI support for this type of work appears to come from the NIST Information Technology Laboratory, but it is unclear whether this is sufficient.

Recommendation 3-1: The Applied Physics Division should consider incorporating artificial intelligence (AI) expertise within the division, rather than just relying on the National Institute of Standards and Technology’s Information Technology Laboratory. Such expertise would allow for the development of a strategic plan for AI capabilities to be organically rolled into the Physical Measurement Laboratory’s work where appropriate.

Developing a Diverse Workforce

Like many organizations that rely on a workforce with expertise in physics and engineering, there is limited diversity in the Applied Physics Division. To address this, NIST has developed a diversity, equity, inclusion, and accessibility (DEIA) plan with specific goals (NIST 2022). PML has ongoing activities that align with the NIST plan. This is laudable, but many of the plan’s goals are inward looking or address DEIA issues at the NIST employment stage. It is desirable to have a more proactive approach to developing the pipeline of future applicants. To an extent, this is being done through engagement with institutions that serve underrepresented minorities (e.g., travel to conferences and to universities)—but even more engagement would be beneficial. The APS Bridge Program could serve as a resource to help NIST seek a more diverse talent pool. The Bridge Program is a post-baccalaureate program lasting 1 to 2 years that provides underrepresented minority students with research experience, advanced coursework, and coaching to prepare them for graduate school admission. Because this program has been in operation for more than 8 years, many graduate students who have participated in this program have started receiving their PhDs and are looking for postdoctoral positions. By approaching key staff at APS, NIST leaders could obtain valuable advice and help in letting students in the program know of NIST’s exciting work in measurement science and NIST’s interest in attracting postdocs from diverse backgrounds.

A longer-term goal is to establish diverse mentors at the upper career levels who can act as attractors for the next generation of diverse scientists. In practice, the PML leadership might partner with the University of Colorado or other host institutions. Beyond this, it is also important to recognize that future participation of individuals from underrepresented minorities depends on addressing needs below the university level. To do this, it is useful to develop laboratory experience opportunities for K–12 teachers, who are trusted mentors who can broaden the perspectives of students who might otherwise be unaware

of the existence of organizations like NIST. This can also be accomplished through outreach of individual scientists into local K–12 schools. Many organizations undertake such activities on an ad hoc basis, leaving staff to self-organize.

BUDGET, FACILITIES, EQUIPMENT, AND HUMAN RESOURCES

The budget is essentially flat funded, but with inflation and rising salaries there is little room for growth. Thus, there are few opportunities for hiring new staff. There was some frustration expressed about this during the panel’s meeting with early career scientists, most of whom were in term positions. There are also few opportunities for obtaining additional expensive equipment. Thus, while funding for current activities is adequate, without additional funding the Applied Physics Division could not act on Recommendations 3-1 and 3-3. In making this assessment it is assumed that the costs for upgrading the laboratory infrastructure (e.g., improving the water supply and protecting against power glitches; see Recommendation 3-2) would not be borne by the division alone.

Facilities

Laboratory facilities in the Applied Physics Division, on the whole, are impressive and adequate for the needs of the scientists; however, there were several challenging situations that directly affect the science. There has been significant improvement in many of the laboratory spaces since the past review, which is a positive development, but more upgrading of the facilities and infrastructure is required. In particular, some of the utilities have issues that are limiting the productivity of the division. The electricity supply is frequently interrupted. These interruptions, even very brief ones, have an impact on many of the experiments and operations within the division. The panel heard that electrical interruptions can ruin experiments in the fabrication laboratories and cleanroom, which result in a setback of several weeks. The technical programs of the organization depend on timely high-quality microfabrication of advanced devices.

Power glitches caused setbacks in many of the other research programs throughout the division. In the Superconducting Circuits for Quantum Information Laboratory, power interruptions would ruin long-term experiments, requiring an automatic alert system to be installed to notify the staff so they could quickly rush to the laboratory at all times, day or night, and reset the equipment. The laboratory was forced to install an uninterruptible power supply to improve their operations. The electrical supply issue needs to be addressed site-wide, with backup power or uninterruptible power devices as needed; otherwise, the facility cannot be considered best-in-class.

There has been a degradation in the quality of the water supply which is causing corrosion in the existing pipes. This has caused the water supply to be contaminated with magnetic particles which affects many of the experiments within the division. An incident was reported in which the poor-quality water and cold weather caused corrosion and a pipe break which flooded a laboratory, ruining expensive equipment. The laboratory required almost a year to recover from this incident. The panel recommends that the quality of the water supply be addressed in order to prevent further incidents.

Recommendation 3-2: The Physical Measurement Laboratory should invest in additional upgrading of the division’s facilities and infrastructure. In particular, the electrical supply needs to be upgraded to avoid the frequent interruptions that have been setting back and ruining experiments, and the water system needs to be improved to avoid pipe breaks.

Equipment: Materials Characterization Tools

There exist a number of materials characterization tools presently within and available to the Applied Physics Division, along with the expected delivery of additional tools in fiscal year (FY) 2024 and FY

2025. While the focus of the division is not primarily on materials science and development, the wide array of devices and experiments under study within the division critically depends on the growth and processing of unique material structures. A concern is that a lack of key characterization tools might slow or inhibit the future development of materials and processes in the critical path to realizing new cutting-edge material structures and devices.

The division’s analytical tools, while extensive in number, are focused primarily on structural characterization; for example, electron and optical microscopes such as scanning electron microscope (SEM), tunneling electron microscope, profilometers, ion beam/SEM, X-ray diffraction, atomic force microscope, secondary ion mass spectroscopy, and energy-dispersive X-ray spectroscopy. The atom probe tomography instrument is extremely valuable, but it is a research instrument, as opposed to a characterization tool.

What is lacking are any tools that interrogate the surface composition of materials used in the fabrication of devices, such as high-resolution X-ray photoelectron spectroscopy and ultraviolet photoelectron spectroscopy. These tools are invaluable in determining the surface and near-surface elemental compositions as well as the presence of contaminants. They can also determine whether the material is metal or semiconducting. Modern XPS systems have high spatial resolution necessary for both blanket films and device structures and software packages typically sold with these advanced systems identify the elemental, chemical, and stoichiometric properties of the materials. These instruments would greatly benefit the materials efforts within the Applied Physics Division. Given that molecular-beam epitaxy is an important growth modality, the suggested characterization tools would optimize and accelerate such process development, including searching for deleterious impurities. These tools can quickly assess the elemental composition of a material surface and the chemical state of the system with small spot capabilities down to and below 1 micron; that is, at spatial scales that are relevant to many of the devices being fabricated and studied in the division, including transmons, transduction devices, and more. There are multiple ways to acquire access to these tools. They can be purchased by the division or through collaboration with other organizations that have these capabilities. Purchasing them would ensure that the division has whatever access to them that it needs to conduct its work, while collaboration could result in work delays while others use the tools.

Recommendation 3-3: The Applied Physics Division should further expand its materials characterization capabilities, as these are critical in constructing some of the devices used in the division’s experiments. New capabilities could include tools that interrogate the surface composition of materials used in the fabrication of devices, such as high-resolution X-ray photoelectron spectroscopy, ultraviolet photoelectron spectroscopy, and molecular-beam epitaxy. The Applied Physics Division should purchase these capabilities to support their work rather than relying on coordinating with others to have access.

Human Resources

Almost 2 years ago the response from the Human Resources (HR) Department (NIST Gaithersburg) regarding personnel actions in hiring and promotions was essentially nonexistent. This lasted for more than a year and was extremely frustrating for the division chief and group leaders. Lack of support from HR affects the division’s ability to hire, promote, and retain good people in a timely way and therefore affects the progress of science. This appeared finally to get fixed, but concerns exist that this could happen again in the future if HR is not prepared to address a higher rate of hiring, such as might be anticipated with the advent of the CHIPS and Science Act of 2022.

There is no HR representative onsite to field complaints about harassment, bullying, ethics issues, etc. There is apparently a well-respected ombudsperson to whom one can go with such concerns. That individual, however, has no authority to launch investigations, and apparently the division chief has had to perform an initial inquiry herself. This presents a serious conflict of interest. There is a need for an

excellent HR person onsite who can take on such issues and launch outside investigations as needed in a timely fashion. Often, with sensitive personnel issues, an in-person presence by an HR professional is particularly helpful and more effective than a remote presence.

Recommendation 3-4: The Physical Measurement Laboratory (PML) should have excellent Human Resources professionals onsite who can address an array of personnel issues in a timely fashion within the context of the PML culture.

Technical Support

Much of the laboratory space that is in use by the PML group is newly refurbished and has been equipped with high-quality instrumentation. The expert installation of equipment and the general setup of the laboratories are impressive, but apparently this has been done by the scientists themselves without the assistance of technicians. Importantly, this also included some rudimentary items such as installing noise damping panels in a cryogenics laboratory. It is impressive that the staff are motivated and capable of doing all of these activities, but it is unclear whether this is the most effective use of research staff hours. The addition of technicians to the staff could free up researcher time to do the work that only the researchers can do.

Laboratory Safety

The safety practices within the division raised some concerns. There have been several serious safety incidents at NIST recently, including a problem with a research nuclear reactor because of an improperly latched fuel rod and a fatality during the demolition of a test structure. According to staff, the Applied Physics Division has periodic safety walk-throughs about every 6 months, which seemed to be less frequent than necessary and not best practices for a research organization with such risks as high-power lasers, power supplies with dangerous voltages, and chemical hazards. During laboratory walk-throughs, the panel noticed that many experimental samples were not labeled with chemical or physical hazards.

Purchasing requirements imposed by the government have caused difficulty in the procurement of personal protective equipment (PPE) for some employees. Proper PPE is an absolute requirement for conducting safe work in PML, especially given the widespread use of powerful lasers, potentially hazardous electronics, cryogenics, and hazardous chemicals.

Recommendation 3-5: The frequency of safety inspections by the Physical Measurement Laboratory (PML) should be increased and PML leadership should reach out to major industrial companies for advice on improving laboratory safety. In particular, the leadership should look to those companies that are recognized as having among the best safety programs in the world. Large chemical and petrochemical companies, for instance, are widely recognized as having very high-quality safety programs and may be willing to share key aspects of their safety practices.

EFFECTIVENESS OF DISSEMINATION EFFORTS

The Applied Physics Division team has a stellar publication record, consistently contributing to high-quality scientific journals renowned in their field. These journals boast an impressive impact factor, reflecting the significance and influence of the published research. The division’s work has consistently appeared in prestigious journals, underscoring its ability to meet rigorous standards of scientific excellence and peer review.

The Applied Physics Division at NIST has garnered exceptional press coverage, reflecting its groundbreaking work and advancements. For instance, Smithsonian Magazine published “New Atomic

Clocks May Someday Redefine the Length of a Second” (Fox 2021). Other articles¹ appearing in a variety of publications have effectively highlighted the division’s significant contributions to scientific research and technological innovation, bringing deserved attention to its accomplishments. By showcasing its achievements to the public and stakeholders, NIST can demonstrate the value and impact of its research, garner support, and attract collaborations. Furthermore, press coverage facilitates knowledge dissemination, allowing NIST’s scientific breakthroughs to reach a wider audience and inspire future generations of scientists and researchers. It also helps foster transparency and accountability, ensuring that tax-payer investments in NIST are recognized as yielding tangible benefits and advancements that positively impact society.

Further Industrial Engagement

For more than three decades the United States has been experiencing the slow but steady loss of fundamental research within industrial laboratories. The decline of Bell Labs is a classic example. Many smaller technology companies do not have the resources or bandwidth to carry out more basic research critical to their needs in areas such as optics, communications, and materials. NIST is known informally by many as “the national laboratory for industry” and the research at NIST is critical to the overall support of U.S. technology industries. Wider engagement is warranted.

The Applied Physics Division does a great job serving industry requests. The following Key Recommendation is not in response to a shortcoming. Rather, it would address some challenges that industries face, which could benefit from an improvement in measurement science that the division does not currently perform. This would be an opportunity for Applied Physics Division to broaden its impact in measurement science.

Key Recommendation 4: The Applied Physics Division should create opportunities to take part in more collaborations that address critical industry needs in measurement science and to generate support for such work.

The Applied Physics Division staff include best-in-the-world technologists pushing the boundaries in multiple disciplines. Its members constitute a high-performing team and, as such, should offer more value to the American industrial ecosystem. The team has an impressive stakeholder community consisting of federal agencies, foreign counterparts, and industrial enterprises. Nonetheless, broader industrial engagement would enable the division to learn more about industry needs and challenges that can be addressed by advances in measurement science and technology. For example, in the semiconductor industry it is necessary to match the critical device dimensions produced in one process chamber with another to within less than 0.5 nm. Typically, such dimensional control is obtained by controlling wafer temperature to less than 0.2 K accuracy and precision for absolute temperatures less than 600 K. Yet, low-temperature pyrometry and similar techniques for measuring the temperature of thin films on Si wafers lack standards to this degree of accuracy, and industry is thus forced to rely on expensive, iterative, and convoluted methods to achieve the desired result. A direct, accurate, and precise temperature measurement would have large value. This is but one example. Similar challenges exist in radio frequency power and fluid flow measurement and control.

There is an opportunity, therefore, for the Applied Physics Division to engage more broadly with industry to understand such challenges and the funding the division would require from the industrial sector to address those challenges. By working to deliver solutions to industrial needs, NIST would be

___________________

¹ See, for example, “Quantum Entanglement Has Now Been Directly Observed at a Larger Macroscopic Scale” in Science Alert (Nield 2021), “Scientists Come Closer to Building Quantum Computer Capable of Solving Virtually Any Equation” in The Academic Times (Gallagher 2021), and “You May Have Missed… Roman Coins Authenticated; Using Sugar to Print Microchips; Aussie Summer Injuries; and the Glow Between Galaxies” in Cosmos (Perfetto 2022).

directly helping industry to create products which could be manufactured with greater precision, more rapidly and cheaply. This would be a great benefit to the nation’s economy and the American public.

REFERENCES