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Quantum Electromagnetics Division
ASSESSMENT OF TECHNICAL PROGRAMS
High-Performance Computing
The Quantum Electromagnetics Division (QED) has an active and externally visible program in quantum computing based on superconducting qubits. This activity leverages NIST’s world leading expertise in superconducting electronics and the laboratory’s many advances in the materials science of Josephson junctions. NIST plays an important role in materials development and analysis, working as a trusted partner to large corporate players in quantum computing, such as IBM. Recent device development at NIST benefits greatly from the well-equipped and well-utilized microfabrication facility. Fabrication capabilities are remarkable. Superconducting device fabrication capabilities are state of the art, and the basis for a broad range of activities across the laboratory. Responsibility for this capability rests within the QED. This is an important service to the entire Physical Measurements Laboratory. Development of quantum accurate arbitrary waveform synthesis in the gigahertz range is under way within the QED. If successful, this exciting project may find applications in qubit control. This project naturally combines NIST’s expertise in quantum voltage standards and single flux quantum logic (SFQ). Through ongoing work in the QED, NIST is positioned to make important contributions to quantum computing for years to come.
Accomplishments
At the well-equipped, well-utilized microfabrication facility, superconducting device fabrication capabilities are state of the art and the basis for a broad range of activities across the laboratory.
Challenges and Opportunities
Development of quantum accurate arbitrary waveform synthesis in the gigahertz range, if successful, may find applications in qubit control.
Quantum Computing
Accomplishments
This group is developing capabilities to verify novel developments from researchers in this field. In addition, the new microfabrication facility is enabling creation of novel devices that optimize performance.
Opportunities and Challenges
In view of the significant efforts from sizeable groups working at IBM and Google, as well as at academic institutions, NIST recognized that it should not be aiming to develop large-scale efforts that would compete with these other sectors. Instead, the group is developing capabilities to confirm performance of devices from these other groups, as is appropriate for a standards group.
Superconductive Electronics
The Superconductive Electronics Group maintains direct current (DC) and alternating current (AC) voltage standards based on the Josephson effect. The Josephson junction’s quantization of magnetic flux make it an ideal frequency-to-voltage converter. Frequency is among the most precisely defined of quantities, an attribute that enables a very precise voltage standard.1
To realize a voltage standard requires synchronous operation of a large number of junctions in series. This is accomplished in part using the resources of the excellent microfabrication facilities that are managed by the QED. Recent advances in voltage standards have been enabled by the development of new material systems that produce better Josephson tunnel junctions. The enablers of these developments included the modernized clean room facilities at NIST.
NIST has used its apparatus developed for electronic measurements of Boltzmann’s constant in the development of a fundamental method to measure temperature without using fixed points and extrapolation. This work will harness the Josephson quantum AC voltage generator that has recently been developed by the same group.
Using the advanced thin-film facilities of the new clean room, the group has developed an improved material, niobium-doped silicon, for the Josephson tunnel barrier. This allows more reliable production and more reproducible and precise operation of the voltage standard. Moreover, work in the Spin Electronics group has further modified the manganese-doped silicon barrier material with magnetic inclusions to allow incorporation into novel magnetic random-access memory (MRAM) nanodevices. This synergy of the materials development was a benefit of both the new facilities, and also of the cross-fertilization within the division.
Accomplishments
The group has realized a programmable DC voltage standard that has demonstrated accuracy to nine parts in 1012, has been disseminated to national metrology institutes (NMIs) around the world, as well as to U.S. military primary standards laboratories, 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. Its synthesizers can perform this function from audio to microwave frequencies with the exceedingly small harmonic distortion implicit in a frequency standard.
The group has also played a key role in the electronic measurement of Boltzmann’s constant, in anticipation of its conversion from a measured to a defined quantity.
Additionally, the group has developed niobium-doped silicon for the Josephson tunnel barrier, enabling more precise operation of the voltage standard.
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1 Adapted from National Research Council (NRC), 2016, An Assessment of the National Institute of Standards and Technology Physical Measurement Laboratory—Fiscal Year 2015, The National Academies Press, Washington, D.C.
Opportunities and Challenges
The apparatus that NIST has devised for electronic measurement of Boltzmann’s constant will have immediate application in advancement of the measurement of static temperature, which will concomitantly be unhooked from its current definition utilizing specific physical conditions, such as the triple point of water.
Quantum Sensors
The Quantum Sensors Group develops detectors and readouts used in millimeter-wavelength astronomy, and for x-ray spectroscopy. The latter NIST-produced devices are used in various x-ray beam lines, with x rays generated from circulating electrons that produce intense synchrotron radiation. The group is the leading supplier in the United States of both of these and is the dominant supplier of the complex Semiconducting Quantum Interference Device (SQUID) readouts used to read out the detector signals, usually with time-domain multiplexing.
The future needs in millimeter-wavelength astronomy will be for even larger detector arrays in the instrument focal plane, moving from the present ≈10,000 or so elements to an order-of-magnitude or more detector elements. This will likely require a more highly multiplexed readout. This can be most efficiently accomplished with a newer kind of millimeter-wavelength detector, the Microwave Kinetic Inductance Detector (MKID)—a detector with which the Quantum Sensors Group has experience. A very large number of detector elements can be read out with one on-chip microwave line, using a microwave frequency comb generated and de-multiplexed by room-temperature electronics. This allows a small and practical number of microwave lines between room temperature and the cryogenic environment.
Accomplishments
The group’s detectors and readouts are used in millimeter-wavelength astronomy and in detection of individual soft x rays. The users in the astronomy community of the millimeter-wavelength range, and in the materials analysis, communities using soft x rays, are very well served by these detectors.
Opportunities and Challenges
The future needs for detectors in millimeter-wavelength astronomy applications can be most efficiently accomplished with the Microwave Kinetic Inductance Detector (MKID). Development of the latter is in its beginning stages at NIST, and the development and integration of such superconducting detectors is a significant skill of the NIST group.
Spin Electronics
The Spin Electronics Group is concerned with the frontiers of measurement of magnetic devices and phenomena essential to small-scale and high-frequency spintronic devices. MRAM is an example of such devices. (As discussed above, in the section, Superconductive Electronics, the Group has further modified the manganese-doped silicon barrier material with magnetic inclusions to allow incorporation into novel MRAM nanodevices.) MRAM has been an also-ran contender for computer memories for decades, even though it is superior to the semiconductor dynamic random-access memory (DRAM) by being nonvolatile and by being faster and superior to flash memory because it’s fatigue-proof. It also attracts interest due to its being radiation resistant. A perennial problem with such devices has been
scaling with respect to write current—current density did not scale downward properly as device size was decreased. This dilemma has now changed with the invention of spin-torque writing, which improves as devices get smaller. MRAM is now a hot topic for future high-performance, low-power computers.
The projects in this group span the gamut from basic physics to the understanding of (external-partner-produced) devices’ defects and error performance. The group’s expertise in high-frequency and nanoscale measurements and its partnerships with industry and universities afford it a unique advantage for advancing the art in this rapidly growing field. The staff have a fine mix of laboratory skills and physical understanding. The creativity found on the laboratory tours was noteworthy.
Accomplishments
The new e-beam tool in the clean room makes it possible to produce test samples in the 10 nm range, which, while below the range of interest for Josephson devices, are perfectly relevant for memory chips.
Opportunities and Challenges
The invention of spin-torque writing, which improves as devices get smaller (i.e., as they scale), makes MRAM a promising topic in the development of future high-performance, low-power computers.
Spintronics
The QED supports a successful program focused on non-Boolean spintronic computing; spectroscopic measurement of spin-charge transduction; and magneto-optical measurements of spintronic materials. (These activities are carried-out in the Spin Electronics Group and the Nano-scale Spin Dynamics Group.) In this area, the division impressively balances core activities in measurement development with simultaneous production of exciting new results in the fundamental science of magnetism. For example, experiments employing the ferromagnetic resonance (FMR) world-record sensitivity, developed within the group, have identified ultra-low damping in binary compounds of cobalt and iron. The Nano-scale Spin Dynamics Group has also used inelastic photon-magnon scattering (Brillouin light scattering) to study the relationship between interfacial Dzyaloshinskii-Moriya interaction (DMI) and Heisenberg exchange interactions in thin metal films, demonstrating for the first time their proportionality. The development of heterodyne magneto-optic microwave microscopy within the group holds promise to interrogate magnetic properties of individual nano-magnets as small as 10 nm. The group is also collaborating with faculty at University of Colorado to build a system for time-resolved extreme-ultraviolet magneto-optics for time-resolved studies of spin dynamics in magnetic multilayers. This is a wise combination of local expertise to develop a new probe of magnetic systems that will surely yield new information.
The aforementioned development of measurement techniques are great examples of how NIST’s core mission also generates understanding of key physical mechanisms underpinning the operation of technologically important materials.
Accomplishments
The Nano-scale Spin Dynamics group has utilized FMR with world-record sensitivity to identify ultra-low damping in binary compounds of cobalt and iron. The group demonstrated the proportionality of the relationship between interfacial Dzyaloshinskii-Moriya interaction (DMI) and Heisenberg exchange
interactions in thin metal films, using inelastic photon-magnon scattering (Brillouin light scattering). While the research thrust in quantum computing is visible both within NIST and externally, the quality of the work in the area of spintronics also deserves recognition and strong support from NIST.
Opportunities and Challenges
The group’s development of heterodyne magneto-optic microwave microscopy will, if successful, facilitate experiments that interrogate magnetic properties of individual nano-magnets as small as 10 nm. A further area of promise is the development, with University of Colorado, of a system for time-resolved extreme ultraviolet magneto-optics for time-resolved studies of spin dynamics in magnetic multilayers.
Optical Medical Imaging
The Optical Medical Imaging Group is providing standardized benchmarks, known as phantoms, for state-of-the-art biomedical optical imaging techniques. The group has developed a layered phantom for optical coherence tomography (OCT), a widely used tomographic technique for imaging the layers of the retina to find disease. There is a significant lack of imaging standards by which these instruments are calibrated. The group has demonstrated fabrication using techniques developed in-house and is preparing to disseminate the phantoms by offering them for sale. Another phantom is under development for photoacoustic tomography (PAT), a recently developed technique that enables depth-resolved imaging of hemoglobin through thick tissues by combining the biochemical specificity of light absorption with the deep penetration of ultrasound. The phantom is based on creating precision distributions of carbon nanotubes, which offer uniform absorption across the visible spectrum. This phantom is in a developmental stage and will likewise provide a much-needed standard for researchers developing PAT instrumentation. A third area of emphasis is to develop a phantom that can be used to calibrate measurements of hemoglobin oxygen saturation. The group possesses a state-of-the-art hyperspectral imaging system, which will enable its development. This is a much-needed resource across the field, as it can be quite difficult to create accurate oxygen saturation distributions.
Accomplishments
Responding to a national need for standardized imaging benchmarks, the group has developed a layered phantom for OCT and begun dissemination.
Opportunities and Challenges
The group is developing a phantom to serve as an imaging standard for PAT. It is likewise developing a phantom that can be used to calibrate measurements of hemoglobin oxygen saturation. Both these endeavors respond to the need for instrument calibration to be standardized across research groups nationwide.
Remote Sensing Laboratory
The Remote Sensing Laboratory Group is conducting measurements of atmospheric gasses, such as carbon dioxide and methane, using differential absorption LIDAR. This is an important area of research, but there seems to be a disconnect with its application to environmental monitoring between the
monitoring and sensing tasks, on the one hand, and the environmental impact, on the other. The group employs unique sensing capabilities such as the use of high power, multi-frequency tunable laser lines to monitor atmospheric gases with high sensitivity and specificity. They have implemented an impressive gantry on the fifth floor that enables them to conduct these measurements. This new facility is still under renovation but will provide a suitable site with rooftop access for continued research.
Accomplishments
The group is using the technique of frequency combs to develop unique sensing capabilities and has implemented an impressive gantry as platform for these unique measurements.
Opportunities and Challenges
The environmental monitoring researchers need to establish clearer linkages between the sensing and monitoring tasks that detect atmospheric constituents and the imputed environmental impacts.
Boulder Microfabrication Facility
As noted in the 2015 review,2 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.3 The recently added e-beam lithography tool has allowed greatly enhanced resolution (below 10 nm), which is essential for magnetic sensors and devices.
The precision imaging facility (PIF), managed by the Applied Physics Division, offers a variety of microscopy tools, including some relatively uncommon techniques, such as local-electrode atom probe and helium ion microscopy.
An innovation at the BMF, is its unique and successful scheme for handling fabrication requests. Instead of allowing numerous amateurs in the clean room, which would degrade it, or going to a full-service system, which would swamp it with sample requests and billing nightmares, the group instituted a system whereby a small, dedicated staff works with super-users from the requesting groups who help maintain the tools essential to their own projects. Among other things, this has kept the facility working at near-optimal capacity while turning out thousands of extremely useful sensors, programmable Josephson arrays, and test samples. One measure of that operational success is that they are making magnetic-atom-doped spin-torque oscillators in the same facility as yield-critical Josephson arrays, without mishaps and with collegiality between groups.
The new clean room has been key in allowing production of the large (150 mm) wafers that are essential in current and future astronomy projects. The cross-fertilization of the thin-film materials ideas has been notable, and likely is facilitated by the flexibility of the clean room equipment and the non-rigid arrangement of user/maintainer people.
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2 National Research Council, 2016, An Assessment of the National Institute of Standards and Technology Physical Measurement Laboratory—Fiscal Year 2015, The National Academies Press, Washington, D.C.
3 NRC, 2016, An Assessment of the National Institute of Standards and Technology Physical Measurement Laboratory—Fiscal Year 2015.
Accomplishments
The group has maintained the microfabrication facility’s impressive capabilities, adding e-beam lithography tool has allowed greatly enhanced resolution (below 10 nm), essential for magnetic sensors and devices. They have kept the facility working at near-optimal capacity while turning out thousands of extremely useful sensors, programmable Josephson arrays, and test samples.
Opportunities and Challenges
Continuing the cross-fertilization of the thin-film materials ideas represents an opportunity, and likely is facilitated by the flexibility of both the clean room equipment and the users and maintainers.
General Comment
This division has commendably maintained continued focus on standards and calibration devices, in spite of the siren song of doing basic science and technology research. The numerous projects that reflect this core responsibility of NIST are very well served in the projects that were reviewed. Who would do them properly if NIST didn’t?
PORTFOLIO OF SCIENTIFIC EXPERTISE
The QED is best in the world with respect to Josephson standards and also millimeter-wavelength astronomy detector arrays. The large testing capabilities at NIST are fully appropriate for almost all near- and medium-term astronomy applications in ground-based observatories. These observatories employ the same kind of large cryogenic systems that are at NIST.
The technical programs reviewed are at the leading edge of measurement and are adequate to meeting their stated goals. While the program in quantum computing is visible both within NIST and externally, the quality of the work in the area of spintronics deserves similar recognition and strong support from NIST.
The quantum computing effort is a partnership with large industrial teams and is also externally visible in its own right through its publications and conference presentations. The QED works to understand the material science needed for highly coherent qubits. This is a valuable service to the community. It appears well-coupled to stakeholders. The Spintronics Group also performs within several large-scale collaborations with industrial partners, providing valuable service to the community. It also has an impressive record of high-profile publications originating at NIST, which further amplify the group’s impact. The Spintronics Group deserves recognition as it seems to couple to stakeholders needs and generate high-quality science in equal measure.
The Quantum Computing and the Spintronics groups have strong technical expertise within their ranks. The Spintronics Group appears to have a broad range of measurement expertise. The Quantum Computing Group’s core expertise is in material science of materials used for quantum computing. It is also involved in device design and circuit testing. As currently configured, the group is well positioned to perform as a collaborator on large-scale quantum computing programs of the sort typically led by larger players in industry and academia. This is a strong position for NIST.
The QED has a good mix of experts, both senior and more junior. Recent retirements have been manageable, and the more junior researchers are also impressive. Being located in Boulder appears to be an advantage in attracting new staff.
FACILITIES AND EQUIPMENT
The QED facilities at NIST are among the best in the world, with the exception of the physical state of the older buildings. The clean room facility is state of the art and well run. It is the cornerstone of much of the division’s success in quantum computing voltage standards, and spintronics. The measurement laboratories appear to be well-equipped with the latest technology. The laboratory space is adequate in size, but improvements need to be made in environmental control. A bucket in a hallway catching rainwater, observed during the laboratory tour, was a reminder that the older buildings were built a half-century ago.
The new clean room has been key in allowing production of the large (150 mm) wafers that are essential in current and future astronomy projects. The cross-fertilization of the thin-film materials ideas has been notable and likely is facilitated by the flexibility of the clean room equipment and the non-rigid arrangement of user/maintainer people.
Accomplishments
The QED has maintained the microfabrication facility’s impressive capabilities, and adding the e-beam lithography tool has allowed greatly enhanced resolution (below 10 nm), essential for magnetic sensors and devices. The facility has been working at near-optimal capacity while turning out thousands of extremely useful sensors, programmable Josephson arrays, and test samples.
Opportunities and Challenges
The environmental controls in the laboratory space need to be improved. The aging facilities have problems with the building envelope, such as the observed roof leaks.
DISSEMINATION
Dissemination of outputs varies (appropriately) by project. Standards projects are expected to have infrequent publications aimed at a small and focused audience. Device and physical phenomena projects are of much wider interest and require conference and journal publication. Patent applications and patent-protective publications have been inadequate and seem to require a more pro-active policy by management. However, unlike journal publication, which is subject to peer review and subsequent citation count, patent activity and its resulting impact are difficult to evaluate in the short term. It is easy to stimulate an increased number of worthless patent applications. Therefore, the QED would benefit from increased guidance in this area.
The division has demonstrated laudable use of guest scientists, students, postdoctoral researchers, and visiting researchers as a way of increasing technical vitality and spreading NIST expertise and knowledge to the outside world. It broadens the impact of their device and technique advances, especially in astronomy, where there is a large U.S. community that will benefit by learning more, in a hands-on fashion, than is accomplished from reading publications about microfabrication. The posting of a Stanford University graduate student to the device fabrication group is a good example of how such technology transfer can be done to benefit both sides.
Accomplishments
The division’s use of guest scientists, students, postdoctoral researchers, and visiting researchers increases both its technical vitality and the spread of NIST expertise and knowledge to the outside world.
Opportunities and Challenges
The division would benefit from increased guidance on the value to NIST of its patent activity vis-à-vis journal publications and other metrics.
