Applied Physics and Quantum Electromagnetics Divisions
INTRODUCTION
The Applied Physics Division (APD) and the Quantum Electromagnetics Division (QED) were recently formed by a restructuring of the former Quantum Electronics and Photonics Division and the former Electromagnetics Division. This restructuring came about as a consequence of the formation of the NIST Communications Technology Laboratory, to which roughly 67 staff members of the two former PML divisions were transferred. Because the two new divisions have considerable overlap of activities and focus, they were assessed together.
These divisions have aligned their activities into five focus areas: quantum information, nano-magnetics, imaging science and technology, sensing, and measurement services and standards.
Applied Physics Division
The APD develops measurement science over broad spans of the electromagnetic spectrum, addressing national priorities that include advanced manufacturing, national security, quantum science, climate change, and biomedical imaging. It consists of seven technical groups: Advanced Microwave Photonics Group, Faint Photonics Group, Fiber Sources and Applications Group, Magnetic Imaging Group, Sources and Detectors Group, Quantitative Nanocharacterization Group, and Quantum Nanophotonics Group.
The Advanced Microwave Photonics Group focuses on microwave generation and detection of quantum information (QI) for both quantum communication and computation. The Faint Photonics Group addresses few-photon generation and detection for quantum communication and secure random number generation. The Fiber Sources and Applications Group addresses high-power lasers and their application to manufacturing. The Magnetic Imaging Group addresses calibration and standardization of magnetic resonance imaging (MRI) and interfaces with an MRI industry standards group. The Sources and Detectors Group develops high-dynamic-range laser power metrology over a broad spectral range. The Quantitative Nanocharacterization Group develops novel optoelectronic scanning probes for a variety of applications, including semiconductor technology, condensed matter physics, biology, and medicine. The focus of the Quantum Nanophotonics Group is on using the entanglement of quantum states to encode information and by applying techniques for manipulation and measurement of the quantum states of atoms, ions, spins, superconductors, and cavity quantum electrodynamics (cavity QED).
Quantum Electromagnetics Division
The QED investigates foundations of techniques for metrology of electronic, magnetic, and photonic technologies. It develops devices, systems, standards, and measurement methodologies to address national needs in these areas of technology. It consists of seven technical groups: Microfabrication Group, Molecular and Bio-Photonics Group, Nanoscale Spin Dynamics Group,
Quantum Processing Group, Quantum Sensors Group, Superconductive Electronics Group, and Spin Electronics Group.
The Microfabrication Group runs the recently built microfabrication clean room facility, which houses the molecular beam epitaxy (MBE) epitaxial materials facility, designed for processing the unique materials required for the extensive experimental QI research programs at NIST. The Molecular and Bio-Photonics Group specializes in quantitative medical imaging using a variety of optical methods. The Nanoscale Spin Dynamics Group develops metrology and studies fundamental physics of magnetodynamics in nanoscale magnetic devices and model systems. The focus of the Quantum Processing Group is development of novel materials, devices, and measurements for the integrating quantum systems in information processing architectures. The Quantum Sensors Group develops advanced superconducting photon detectors and amplifiers that are sensitive on the single-photon level over a broad spectral range and applies them to diverse fields such as astrophysics and chemical dynamics. The Spin Electronics Group develops metrology and fundamental understanding of spin currents and their application in nanoscale magnetic devices and hybrid magnetic/superconducting memory devices. The Superconductive Electronics Group develops and characterizes voltage standards based on quantized magnetic flux in superconducting Josephson devices and investigates devices for advanced computers based on superconducting logic and memory.
ASSESSMENT OF TECHNICAL WORK AND DISSEMINATION OF OUTPUTS
Quantum Information
Quantum Optics and Processing
Quantum optics and processing activities fall under the overall topic of quantum processing, which includes novel measurements and devices for the integration of quantum systems into information processing architectures. On a larger scale, QI is the application of ideas of quantum physics to the area of information sciences.
An important matter being addressed is using the principle of entanglement by encoding information in the quantum mechanical state, which involves the manipulation and measurement of quantum states of atoms, ions, spins, superconductors, and cavity quantum electrodynamics. The group is creating tools for generating, manipulating, detecting, and measuring photons under various conditions.
Transportation of information encoded using quantum states of matter or light has been shown to be desirable by assuring that unauthorized eavesdroppers cannot decode the information. This is often called teleportation of information, which is a subject of intense research activity around the world. The quantum information subgroup within the Faint Photonics Group and the Quantum Nanophotonics Group has demonstrated quantum teleportation over a distance of 100 km of optical fiber, which is approximately four times that of the previous record. This feat was possible because of the high-efficiency single-photon detector capability, which is described in the quantum sensors section of this chapter. Teleportation over optical fibers brings the ability to transmit quantum encoded information into the practical realm.
Application of quantum physics to the area of information sciences involves the use of ion traps that retain the ions for a long time, which requires reduction of anomalous heating that results from surface contamination and ordering. Paying special attention to cleaning of the surfaces reduces heating. The group has attained a 100-fold decrease in ion trap heating rates via in situ cleaning of carbon contamination, which allows the traps to operate with much lower ion height. Quantum computing may have immediate application in the area of true random number generation.
This activity at the Applied Physics Division is among the many similar outstanding activities around the world. The division’s activity is not at the fundamental leading edge of science, but it is taking
advantage of the superb photon sensors that the PML has developed. This activity is contributing well toward bringing QI science into practice, even though it may take many years to accomplish that.
Advanced Microwave Photonics
The microwave photonics effort in the QI and measurements project is impressive. The creation of entangled photons is a major challenge for quantum computing. Making use of microwave nonlinearities for generation and detection of QI greatly reduces both fabrication and instrumentation challenges in exchange for carrying out the experiments at much lower temperatures, less than 30 mK. Progress in low-temperature technology over the past decade and readily available, well-established, and extensive microwave instrumentation make this an excellent trade-off, particularly in light of the strong PML expertise in superconductive materials, device design, and characterization.
Creation of controlled-NOT (C-NOT) gates and experimental investigation of QI are impressive. This is part of the more extensive QI project that covers both more conventional photonic and superconducting Josephson junction approaches, so the entire effort is highly complementary and covers a broad range of approaches in this very challenging, long-range program.
Quantum Nanophotonics
The focus of the integrated photonics effort is the development of a quantum repeater for quantum communications. Quantum optical communications requires generation and detection of single photons to produce entangled photon pairs. The project is developing sources and detectors for quantum states of light based on self-assembled quantum dots embedded in high-Q photonic crystal optical cavities for application to single-photon sources, laser diodes, and quantum optical metrology. Integrated quantum dot gain regions in high-Q cavities produce very short radiative emission times, increasing the speed and efficiency of the light source, which are critical enablers for quantum communications.
The Quantum Nanophotonics Group has demonstrated both quantum-dot-based detectors and lasers of single photons that are unique in the compound semiconductor device world. The group recently demonstrated a wavelength bistability phenomenon in a monolithic quantum dot laser. This effort couples well with the efforts of other PML groups in the quantum information program.
Nanoscale Magnetics
Spin Electronics and Nanoscale Spin Dynamics
The projects of the Spin Electronics Group and the Nanoscale Spin Dynamics Group build on their previous work on understanding and measuring the magnetic behavior of microscopic ferromagnetic film devices. These groups continue to demonstrate the world’s fastest measurement of magnetization dynamics. The groups also demonstrate microwave ferromagnetic resonance measurement of the smallest magnetic features with the highest dynamic range. It now appears that magnetic switching by use of spin currents will play an important role in future magnetic storage devices. The work of these two groups continues to provide a fundamental understanding of these phenomena. People in industry will use this work for guidance on how to make these extremely difficult measurements, which will be essential for understanding the failure modes of nanoscale spintronics in commercial applications.
Several important investigations push the frontiers of magnetic-based oscillators and of our understanding of dynamic effects (such as magnetic damping during switching). Others provide insight into the thermal stability of microscopic-domain configurations (i.e., stored bits). The data obtained and the techniques perfected are certain to prove useful in the development of future low-power, high-speed
computers. This work is entirely in line with the NIST directive to further the national strategic computing initiative.
Imaging Science and Technology
Magnetic Imaging
The biomagnetic imaging program focuses on several issues related to MRI. Central to these efforts is the development of techniques that make it possible to ensure that the images produced with different scanners will reflect underlying pathologies in a consistent manner. At the heart of these efforts is the development of standardized phantoms, nonbiological fabricated artifacts that can be imaged in an arbitrary scanner to identify differences in the images produced by different machines. A particularly good example is a head phantom that contains an array of solutions designed such that each has a well-defined diffusion coefficient for water. Diffusion is often used as a contrast mechanism in MRI, and it can be very important for diagnosing conditions such as traumatic head injury. Diagnosing such injury, however, requires making subtle distinctions that require high levels of standardization in the response of the scanner if results are to be compared from one machine to another. The head phantoms are now being commercialized and are undergoing clinical trials. Another example is breast phantoms that simulate the healthy tissue. It can often be the case that a scanner will produces images with what appear to be morphological anomalies, potentially tumors, that are in fact nothing more than artifacts traceable to imperfections in the MRI scanner. Having a standardized phantom that is known to have no features corresponding to tumors makes it possible to ensure that a particular scanner will not be prone to producing false positive results.
Another area of focus in the biomagnetic imaging program is the study of so-called MRI contrast agents. Historically, contrast agents have been largely limited to injectable substances that, when present, increase the brightness of the MR image. Gadolinium-based compounds, for example, have been very useful for visualizing vasculature. One can imagine, however, contrast agents that provide sensitivity to different biological or chemical characteristics. One PML-developed contrast agent utilizes nanofabricated structures that respond resonantly to radio-frequency (RF) radiation. The resonant frequency of these structures is sensitive to the local pH, making it possible to use MRI to visualize certain details of physiological processes. The approach of using such nanofabricated structures has considerable potential for future applications as well.
Molecular and Biophotonics
The Molecular and Biophotonics Group works to develop methodologies for quantitative optical medical imaging based on several diverse techniques, including optical coherence tomography (OCT), hyperspectral imaging (HSI), photoacoustic imaging, and light scattering methods. They do this by advancing measurement science supporting these techniques and by developing calibration and characterization tools that can make these technologies quantitative and international system of units (SI) traceable. This effort to standardize and develop quantitative tools is of key importance and has the potential for significant impact in laying a foundation for reproducible medical research that can be applied to recognize biomarkers for early disease recognition and to measure short- and long-term response to therapy. Optical imaging methods are advantageous in being mostly noninvasive, utilizing nonionizing radiation, and providing high-resolution, label-free imaging.
Examples of recent technical accomplishments include improvement of OCT resolution to 1 µm, label-free chemical mapping of subcellular molecules at the single-cell level using HSI, and the development of a unique hyperspectral dark field microscope for optical biopsy. This microscope has been deployed in a clinical environment to address a particular deficiency in the rapid, accurate
determination of tumor margins in breast cancer, which currently leads to the need for additional surgeries in about half of lumpectomy patients. The rapid-turnaround detection of precise tumor margins available once this instrument is present in the operating room will allow surgeons to make decisions in real time and reduce the likelihood of second surgeries.
Relatively few of the large number (∼160,000) of biophotonics-related patents have penetrated the market to become devices approved by the Food and Drug Administration (FDA). Thus, a particular challenge and significant opportunity for external impact is to enable accelerated FDA approval for advanced biophotonic imaging methods. The PML addresses this issue by developing quantitative standards that help to improve measurement quality and lead to faster FDA approval for tools developed by the biophotonics community. Advances toward this goal will be key in maximizing the impact of advanced optical imaging on future delivery of health care. This group has a variety of external collaborators, including academic institutions, instrumentation companies, and other government agencies. Further evidence of the technical quality and success in dissemination of the results of the group’s efforts is the output of published papers and invited talks (about five per year of each for the past few years).
Quantitative Nanocharacterization
The Quantitative Nanostructure Characterization Group has developed an advanced optoelectronic probe tip for near-field scanning microscopy that is based on the integration of gallium nitride nanowires with silicon scanning probe cantilevers. They have perfected the growth of these nanowires and demonstrated their use as probe tips for scanning microwave microscopy measurements of carrier concentration and conductivity in semiconductor nanostructures and 2D electronic materials, an application where the exceptional durability of the nanowire tips has enabled more quantitative measurements. The nanowires can also be doped during growth and potentially excited electrically as a light-emitting diode, providing simultaneous force, optical, and microwave susceptibility sensing. This will enable simultaneous detection of changes in electrical properties upon optical excitation directly from the scanning probe, with high temporal and spatial resolution, for example, when applied to characterization of photovoltaic materials.
The realization of this optoelectronic nanowire probe presents a difficult technical challenge. The eventual impact of this technique on advanced manufacturing remains unclear; the demonstration of its application to the solution of a key measurement problem of importance to industry would be a significant advance.
Precision Imaging
The precision imaging facility has impressive capabilities for materials characterization at the atomic and nano scales. These capabilities are primarily used to support the other materials development capabilities, as well as outside clients who have specific metrology needs that can be served by use of these tools. The tools appear to be staffed by highly knowledgeable scientists who publish their work frequently in archival journals and at conferences. Two of the many noteworthy instruments/capabilities are the He ion microscope and the near-field scanning microscope.
The He ion microscope is a new instrument that has been purchased because of its exceptionally large depth of field—an extremely important capability for imaging nanostructures with considerable surface morphology. The second unique capability is a near-field microscope using light-emitting GaN tips. These tips require a considerable degree of expertise to fabricate, but ultimately they allow for the local (at the nano scale) illumination of a sample to observe separate optically active regions. Several other, more standardized pieces of equipment comprise the suite of capabilities in the 3,000 ft2 facility. The facility appears to be well supported by NIST.
The capabilities and high-quality staffing of the facility play an essential role in supporting both the internal (to NIST) and external materials research communities in the United States.
Sensing
Quantum Sensors
Quantum sensors activities cover precise measurements of the energy carried by photons or particles, the development of sensors, and supporting technology to perform these measurements and apply these sensors to problems with scientific and technological relevance. The core technologies include transition-edge-sensor (TES) calorimeters, superconducting quantum interference devices (SQUID) readouts, and superconducting microresonators.
The photon detection capability developed by the Quantum Sensors Group is now made available for application to practical problems. Application areas include astrophysics, x-ray physics, and laboratory science. The group is among the best in the world in the fabrication of high quantum efficiency integrated transition edge sensors (TES) and ultra-low-noise SQUID readouts for photon detection over a broad range of photon energies. The group expects to reach nearly unity detection efficiency in the future. Upon detection of an incident photon, the signal magnitude is proportional to the photon energy; the TES thus functions as a spectrometer as well as a detector. The TES has shown the capability to reproduce detection of one and more photons. When compared with other gamma-ray sensors the TES sensors show much higher resolution and sensitivity. TES detectors are being integrated into spectrometers deployed in the National Synchrotron Light Source and the Advanced Photon Source. The group also has an x-ray spectrometer under construction for the Stanford Synchrotron Radiation Light Source. A 16 pixel version has been commercialized for semiconductor defect analysis. For analysis of plasma sources, which are very dim compared to the synchrotron sources, the high-resolution, high-efficiency detectors’ superconducting x‐ray sensors fabricated by the group are ideal for measurements at the 10−12 meter scale and the 10−12 second time scale for dynamic measurements.
This group is very successful in technology transfer to private industry, to academic and government laboratories, and for astronomy polarimeters, where more than 20 installations of TES/SQUID-based detectors and detector arrays are playing a central role in millimeter wave polarimetry in astrophysical cosmology. PML detectors and/or amplifiers are in almost all millimeter wave polarimeters in the field, because these detectors provide the best performance.
This Quantum Sensors Group and the Quantum Nanophotonics Group have also built a unique tabletop time-resolved x-ray spectrometer based on a femtosecond laser source that is focused into a water jet to generate pulses of x rays. The high sensitivity and quantum efficiency of the TES sensors are a good match to the relatively low x-ray flux, and this is the key enabler that makes this experiment possible without the high x-ray flux of a synchrotron or free-electron laser source. This instrument is used in novel studies of chemical dynamics through time-resolved, x-ray, near-edge spectroscopy and x-ray absorption fine structure.
The PML group deserves congratulations for the success of its TES activity, which has resulted in a uniquely versatile and capable detector technology that has been successfully propagated to many laboratories around the world.
Precision Optical Measurements
The Fiber Sources and Applications Group demonstrated a new technique based on dual frequency comb spectroscopy that can accurately measure amounts of major greenhouse gases. The concept entails sending a laser beam across a 2 km round trip path from NIST to a mirror mounted on the side of a nearby mesa. This provides a test column whereby even trace amounts of methane can be
detected with very high sensitivity. The research team has collected data under real conditions and compared the data against data collected at a nearby National Oceanic and Atmospheric Administration (NOAA) point sensor under well-mixed atmospheric conditions.
The PML measurements yielded concentration uncertainties of less than 1 ppm for carbon dioxide, validating the concept. The group has extended this method to differential absorption light detection and ranging (LIDAR) that measures both mass flux and gas content along this volume as a means of obtaining the distribution of greenhouse gases. This allows for pinpointing local sources and perhaps ultimately their remediation. Extension to portable laser systems, which is one focus of this team, will enable its widespread deployment to sites around the United States and worldwide to help in the accurate measurement of greenhouse and other atmospheric contaminants and of their sources. This is a vital precision measurement capability that lies at the core of the NIST mission of determining the trace presence of contaminants and other materials in the environment.
Measurement Services and Standards
Superconductive Electronics
The Superconductive Electronics Group has created and maintains both direct current (DC) and alternating current (AC) voltage standards based on the Josephson effect. The quantization of magnetic flux in a Josephson junction make this device a perfect frequency-to-voltage converter; since frequency is perhaps the most precisely defined quantity, this provides a path to a very precise voltage standard.
Realization of a voltage standard requires synchronous operation of a large number of junctions in series, which is enabled by the excellent microfabrication facilities that are part of the Quantum Electromagnetics Division. The resulting programmable DC voltage standard has demonstrated accuracy to a few parts in 1011, has been disseminated to national metrology institutes (NMIs) around the world, and is available for sale as a certified NIST reference instrument. This group is the best in the world in AC waveform synthesis with quantum-derived accuracy and in the electronic measurement of Boltzmann’s constant to 3 ppm accuracy.
The Superconductive Electronics Group also works to develop superconductive logic and memory devices for advanced high-performance computing. This is a national priority area identified in the National Strategic Computing Initiative, and the group is well suited and equipped to make advances in superconducting computing.
Laser Metrology and Applications
The Sources and Detectors Group has performed impressive laser metrology work. Because of the extreme sensitivity of the welding process to the control of laser welder power. PML involvement in setting power measurement standards is important to the U.S. economy.
The work on metrology is very imaginative and impressive. The standard approach is to measure coolant temperature changes from output absorption in metal power-absorbing cells. This method is effective and reasonably accurate; however, it is expensive and does not clearly provide a portable standard that can be used in house by any but the most substantial laser welder manufacturers or users. The new approach being explored by the Sources and Detectors Group is to measure radiation pressure using commercially available scales. The power is measured by determining the change in scale reading in the presence of and the absence of the incident beam. The method is very inexpensive and may provide the accuracy required for many manufacturing needs.
The purchase of a new welding tool is an important addition to the metrology group, which can do real-time experiments to determine the variables that need to be measured and controlled in practical welding applications. The group already has proficiency in its use.
The Laser Metrology Group is doing excellent work in support of this broad-spanning and crucial component of our national economy. The group holds a global leadership position in high-power laser metrology.
PORTFOLIO OF SCIENTIFIC EXPERTISE
The permanent staff members of the APD and the QED form a talented group, as evidenced by their scientific output, the recognition of 3 of their staff as NIST fellows, and of 14 of them as fellows of scientific professional organizations, and by their recognition as recipients of 8 external awards and 32 NIST or Department of Commerce awards since 2010. They are active and well recognized for their contributions to conference organizations and professional societies. They have averaged about 5 refereed publications per staff member since 2013, for a total of over 250 publications. Their publications were cited 5,335 times in 2014. These scientists exhibited exceptional depth of knowledge and understanding of their fields of expertise.
ADEQUACY OF FACILITIES, EQUIPMENT, AND HUMAN RESOURCES
The MBE laboratories and microfabrication facilities in Boulder and in Gaithersburg are impressive and are designed for the processing of the unique materials and devices required for research, including the extensive experimental QI research programs at NIST.
The MBE systems in Boulder and Gaithersburg are very new and state-of-the-art. Both facilities have excellent capabilities for growth and optical characterization of the unique quantum structures that are being grown to support the quantum device projects on entangled photons and single-photon detectors.
The state-of-the-art Boulder Microfabrication Facility (BMF) provides clean-room facilities and fabrication tools vital to the success of many of the technical groups, such as the Quantum Sensors and Superconductive Electronics Groups. The BMF has impressive capabilities for materials deposition and for sophisticated fabrication of superconductive tunnel junctions and semiconductor quantum well, dot, and nanowire structures.
The precision imaging facility (PIF) offers a variety of microscopy tools, including some relatively uncommon techniques such as local-electrode atom probe and helium ion microscopy.
The Gaithersburg and Boulder nanofabrication capabilities are complementary; the Gaithersburg facilities address Si complementary metal-oxide-semiconductor (CMOS) technology but are unable to meet the demands for the combination of materials grown and processed in Boulder. The processing facilities are state-of-the-art and appear to be staffed by knowledgeable personnel and utilized by a broad range of scientists in the Advanced Microwave Photonics, Magnetic Imaging, Sources and Detectors, Quantitative Nanocharacterization, Quantum Sensors, Superconductive Electronics, Quantum Processing Faint Photonics, and Quantum Nanophotonics groups. The scientists using these facilities publish their work frequently and are active in their respective technical communities.
As an example of the quality of work in the APD, electron beam lithography has been used to pattern nanowires into a thin film made of a heat-tolerant ceramic superconductor, molybdenum silicide, operated at the superconducting transition edge temperature. The new design operates at higher temperatures and current. Timing jitter is now 76 picoseconds and detector efficiencies are at 87 percent at wavelengths that are useful in telecommunications.1
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1 V.B. Verma, B. Korzh, F. Bussières, R.D. Horansky, S.D. Dyer, A.E. Lita, I. Vayshenker, F. Marsili, M.D. Shaw, H. Zbinden, R.P. Mirin, and S.W. Nam, High-efficiency superconducting nanowire single-photon detectors fabricated from MoSi thin-films, Optics Express 23(26), 2015, 33792-33801, doi:10.1364/OE.23.033792.
In the QED, a significant and important advance has been the development of a new kind of sensor that can be used to investigate the isotopic composition of plutonium samples—a critical measurement for nuclear nonproliferation efforts and related forensics, as well as environmental monitoring, medical assays, and industrial safety.
PML staff suggested that the Gaithersburg and Boulder nanofabrication facilities could support a significantly greater number of NIST projects or outside collaborators. These are valuable resources that are not readily available to the growing user community outside NIST.
The Gaithersburg microfabrication facility is older and has been substantially upgraded. A new facility has been established at the University of Maryland.
The recent reorganization of these divisions has balanced the numbers of their staff, with 101 full-time employees and affiliates in the Applied Physics Division and 103 full-time employees and affiliates in the QED, while retaining a distribution across the five focus areas. About a third of the technical personnel in each division are permanent federal employees, with the remainder being mostly affiliates (guest researchers) and federal term employees (postdoctoral researchers). While recent construction has provided new, advanced laboratory space for much of the work in these divisions, the number of postdoctoral researchers has not increased.
It was also noted by the PML that graduate student hiring is substantially hindered by the practice of charging full NIST overhead on the cost of the student, which is then passed to the university, which charges full overhead again on the cost of the student. The resulting concatenation of overheads substantially exceeds 100 percent.
There are few technical support staff members, such as machinists, mechanical designers, instrument builders, and electronics technicians in residence for the areas of applied physics and quantum electromagnetics. This work is divided between external contractors and the special shop facilities personnel at JILA (the joint institute between NIST and the University of Colorado). Continued access to the JILA shops and continued funds supporting work done by external vendors is important for the technical work in these two divisions.
It was also noted by the PML that investments in new capital equipment are charged overhead proportional (approximately 50 percent) to the full amount of the capital cost. This is a serious limitation to the investment in the equipment necessary to maintain the high level of productivity of these two divisions and the PML more generally.
CONCLUSION
The activities in the APD and the QED are well aligned to address the priorities of the PML mission. These priorities are advanced measurement dissemination, photonics, measurement science for future computing devices, quantum information, and physical measurements in biophysics and biomedicine. These divisions excel at advancing the frontiers of measurement science through new technology and at making sure this technology has impact through dissemination of technology and through interactions with key stakeholders in industry and elsewhere. Overall, these divisions are well aligned to contribute to NIST’s maintenance of U.S. leadership in metrology that supports advanced optical manufacturing technologies.
