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Photonics, Electronics, and Quantum Sciences

INTRODUCTION

The U.S. Army Combat Capabilities Development Command (DEVCOM) Army Research Laboratory’s (ARL’s) photonics, electronics, and quantum sciences competency focuses on strategically determining scientific investments to ensure that future technologies will provide full-spectrum information and decision dominance across all domains. By driving new discoveries in photonics, electronics, quantum science, and sensing, the ARL noted in its overview that the competency is striving to avoid a transparent battlefield, reduce technological parity, and exploit information asymmetry.¹

Within the competency are four core competencies: photonics, electronics, sensing, and quantum science. The photonics core competency focuses on low-signature, secure communications; precise timing tools; and multifunctional, high-performance information and sensing systems. Its research focus areas include integrated photonics, radio frequency (RF) photonics, meta-optics, and optical frequency and timing. The electronics core competency focuses on novel functional materials and devices for ultra-efficient, novel electronics architectures and approaches to advance sensing, communications, and processing at the tactical edge. Its research focus areas include topological electronics, ferroelectric field-effect transistors (FeFET), material-design hardware and software ecosystems, and neuromorphic computing. The quantum science core competency focuses on quantum sensing, timing, computing, and networking that exceeds classical limitations. Its research focus areas include neutral atoms, ions, and solid-state defects. The sensing core competency focuses on expanding and fusing sensing modalities, while exploring new concepts in electronic and mechanical sensing. Its research focus areas include deep sensing, position and inertial sensing, multi-modal sensing, decision algorithms, autonomous sensing, and sensor integration.²

On July 23–25, 2024, the Panel on Assessment of Photonics, Electronics, and Quantum Sciences visited the Adelphi Laboratory Center in Adelphi, Maryland. During this visit, the panel viewed podium and poster presentations, toured facilities, and spoke to the scientific researchers within the competency. Below is the summary of its findings as they relate to the assessment criteria. As part of the assessment, the Army Research Laboratory Technical Assessment Board (ARLTAB) and its panels were asked by ARL to provide suggestions of specific people and organizations relevant to the work they were doing, or could be doing, that they could connect with. The fruits of this brainstorming activity are captured in the pages of the following chapter. It is important to note, however, that while certain individuals or organizations are mentioned, the ARLTAB and its panels are in no way being prescriptive about connecting to these outside entities and understand there may be other exemplars of equal value in the

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¹ P. Baker and P. Pellegrino, 2024, “Photonics, Electronics, and Quantum Sciences (PEQS) Competency,” U.S. Army Combat Capabilities Development Command (DEVCOM) Army Research Laboratory (ARL) presentation to the committee, July 23.

² Passages of this introduction come from P. Baker and P. Pellegrino, 2024, “Photonics, Electronics, and Quantum Sciences (PEQS) Competency,” July 23.

research community. ARL should therefore use their best judgement as to whether these ideas could be helpful.

TECHNICAL QUALITY OF THE COMPETENCY

Electronics Core Competency

Accomplishments and Advancements

Overall, the electronics core competency’s research efforts are quite solid—they are significant, broad, and competitive with the research efforts in related laboratories. The priority scientific questions (PSQs) guiding the electronics core competency are reflective of the state of the art in the field. All the efforts from two-dimensional materials, device structures, circuits, and neurally inspired system development are producing cutting-edge research results. The materials and device-related research have a great mixture of intramural and extramural research. The strong device-to-circuit-to-system effort has an excellent intramural effort, although a strong suggestion is to complement this effort with equally strong extramural efforts—this is discussed in greater detail below.

Furthermore, the teams supporting the core competency are using appropriate research methodologies typical of the best integrated circuit (IC) design communities in academia and in other research groups (and commercially). The approach for IC design, IC verification, and IC testing are all consistent with the best practices of top groups in the field. The core competency appears to have a good understanding of research conducted elsewhere. In the area of IC design, they have been growing their research capacities based on knowledge of the field at large and on the device side, the team appears to have a solid understanding of the research in the field.

Additionally, the device-to-circuit to systems thrust is a strong effort produced by the intramural researchers (project name: Neuromorphic Devices for the Tactical Edge). The rising focus on neural networks and neuromorphic techniques is significant and is in a growing technical area.

The technical research decisions to have strong efforts toward non-volatile memories (NVM) focused on what is possible for typical IC fabrication is precisely the right direction to enable transition for other efforts. The NVM focused on FeFET development, and some early efforts in the floating gate capabilities fit well in this methodology, and carefully looking at both techniques are balancing ARL’s research efforts.

In addition, the “Ferroelectric Phase Landscape and Integration into Neuromorphic Devices” poster focused on the development of hafnium zirconium oxide (HZO) as a complementary metal-oxide semiconductor (CMOS)-compatible ferroelectric material for neuromorphic computing devices. The ferroelectric properties of HZO are highly dependent on its crystalline phase and structure, and thus, control of its device-related properties is crucial for technological adoption. ARL is leading a comprehensive and highly successful research program to establish the correlation between the materials synthesis, materials characterization, and device performance of HZO-based FeFETs. An in-depth study of HZO materials preparation and subsequent thermal treatments, along with extensive materials characterization, was performed to develop a robust process to control the device-related ferroelectric properties.

Additionally, the effort along potential neural network circuit architectures, particularly configurable neural network circuit architectures (project name: Novel VLSI Design for Energy Efficient Processing), could result in very significant system-level applications. Furthermore, the focus on developing IC design, tools, and device-to-system stack is extremely important, particularly given all the critical fundamental research along those directions that will help these efforts. Much like materials and other infrastructure capabilities, these capabilities enable a wider range of technical approaches.

Research Portfolio Opportunities

The primary technical suggestion for the device-to-circuit to system group is to add extramural efforts that could complement the intramural research program. There is a significant amount of fundamental research along these lines that could assist intramural efforts, as well as would be complementary. Many university researchers could enhance the research activities, even with 6.2 research activities (as 6.2 research for a university is still considered fundamental research), and therefore can be an important bridge for a number of IC technologies and techniques.

In addition, it is extremely important that ARL is working to build up its analog, mixed-signal, digital IC design, and related capabilities. These capabilities are essential for developing many applications, and often these capabilities limit what can be done with materials and device-level research. A lack of such capabilities can cause limitations for many system designs. Enhancing this research focus is very important, especially in light of the fact that there is a huge shortage of IC design talent and expertise. In addition, ARL could also consider building up research efforts and collaborations on advanced packaging and three-dimensional (3D) heterogeneous integration, which are emerging areas.

6.1 level circuit and systems efforts are being done at many universities, and connecting to such efforts may help to bring this knowledge in-house at ARL. ARL could enhance its extramural network to include current research in digital design, low-power analog design, and mixed-signal design, as well as analog and mixed-signal synthesis tools and configurable analog capabilities. Broadening this research knowledge base would develop a deeper university network of connections to recruit IC research talent to this growing research area—talent that, as mentioned, is often extremely difficult to find and recruit. Building relationships with a number of analog IC groups could be a good place to start. A few suggestions of experts in the field who may provide guidance on developing this research thrust include David Graham at West Virginia University and Siddharth Joshi at University of Notre Dame, Tinoosh Mohsenin at Johns Hopkins University, and Shantanu Chakrabarty at Washington University. In addition, for IC design, one important component to consider is on-chip detection and learning typical of machine learning (ML) accelerators.

Finally, connecting with external researchers could help accelerate some of the device- to circuit-level research, such as consulting a circuit designer with expertise in building polarization imagers (e.g., individuals like Viktor Gruev at the University of Illinois) to complement the ARL polarization imager effort. It was good to see an initial effort with external collaborators during the poster sessions and further university and small company collaborations going forward are encouraged. More broadly, once ARL build’s some of its capabilities, for its overall electronics research, ARL could also consider academic linkages such as University of Texas at Austin’s Texas Institute for Electronics and the Defense Advanced Research Projects Agency (DARPA) Next-Generation Microelectronics Manufacturing effort.

Photonics Core Competency

Research in the photonics core competency focuses on materials development, device and IC design, fabrication processes, and system engineering to achieve extremely complex optical processing in highly integrated, low-power, and compact form factors, and with the capability of high-bandwidth signal processing of optical and traditional electronic functions modulated to optical frequencies. Underlying the core competency is the need for low size, weight, power, and cost (SWAP-C) of system assemblies. Since conventional optical systems consist of bulky optical components that must be painstakingly assembled and aligned, manufacturers around the world are rapidly adopting “optical chip” technology based on a silicon platform that integrates compact passive and active optical devices with electronics on a silicon

wafer to achieve monolithic chip-scale miniaturized optical systems.^3,4 These photonic integrated circuits (PICs) leverage the mature CMOS foundry processes that are used in manufacturing silicon electron ICs, thus enabling scalability and high-volume, low-cost production. Leveraging this mature, yet still evolving, technology, ARL is engaged in developing PICs for a wide range of practical applications, including optical sensing (bio- and chem-sensing), optical communications, microwave signal processing, meta-optics, neuromorphic computing, and emerging areas in quantum photonics. The photonics core competency is multi-disciplinary, and ARL engages in mutual collaborations with universities, other Department of Defense (DoD) research laboratories, national laboratories, as well as manufacturing facilities to enhance and accelerate progress.

Accomplishments and Advancements

The overall scientific quality of the photonics core competency is very high. The intramural work is on par, both in size and scope, with research in the field being done at many large academic institutions, although this is perhaps for good reasons (since some work is not distributable to the public), not captured by the traditional metrics (e.g., number of publications in high-impact-factor journals; average h-index of faculty) by which most university research programs are judged. The extramural research portfolio is focused on selected forefront research areas and includes work at academic institutions (University of Southern California [USC], New York University, Australian National University) that can be considered “research peers” with the ARL photonics research staff. The overall scientific quality of the research being produced by the 18 extramural collaborations is very good, particularly in metamaterials, and includes work by some of the brightest young stars in that subfield (including the 2018 winner of the Adolph Lomb Medal).

Photonic Integrated Circuits

Close collaboration with the American Institute for Manufacturing (AIM) Integrated Photonics and a clear understanding of current and future capabilities of integrated photonic structures puts the ARL team at the forefront of developing new optical chip-based technologies for sensing, navigation, and communications.

• Atomic Layer Deposition of KTa_xNb_(1–x)O₃ Thin Films for Silicon Photonics (Poster). This project focuses on the development of the electro-optic material potassium tantalate niobate (KTa_xNb_(1–x)O₃; KTN) thin films for heterogeneous integration with silicon PICs. Taken together with the poster, “Advanced Nanoscale Fabrication Technologies for Meta-Optics and Integrated Photonic Devices,” it highlights ARLs ability to create hybrid photonic materials that could positively impact PIC performance, component count, and durability. Bulk KTN crystals have very high Kerr nonlinearity, making this material very attractive for optical modulators. Thin films of KTN, on the other hand, are difficult to grow with precise Ta:Nb stoichiometry and crystalline structure. Since the electro-optic properties of KTN thin films are extremely sensitive to these materials properties, ARL is developing a process for the controlled deposition of KTN.

  Currently, there is no thin film deposition method for KTN that is compatible with Si CMOS processing. ARL is leading the field in developing atomic layer deposition (ALD) for the heterogeneous integration of KTN on the silicon platform. KTN thin films are particularly

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³ X. Zhou, D. Yu, D.W.U. Chan, and H.K. Tsang, 2024, “Silicon Photonics for High-Speed Communications and Photonic Signal Processing,” Nanophotonics 1:27.

⁴ S.Y. Siew, B. Li, F. Gao, H.Y. Zheng, W. Zhang, P. Guo, S.W. Xie, et al., 2021, “Review of Silicon Photonics Technology and Platform Development,” Journal of Lightwave Technology 39(13):4374–4389, https://api.semanticscholar.org/CorpusID:233651482.

• difficult to synthesize by ALD because potassium is hygroscopic and very few laboratories have been able to deposit K-containing materials by ALD. Furthermore, K reacts with the Si wafer. ARL has been collaborating with the University of Oslo on the use of K-containing precursors for ALD. Despite these difficulties, using a specially designed ALD reactor, ARL is the first to report KTN on silicon by ALD.⁵ ARL has made significant progress in synthesizing this material and establishing heat treatment processes to control the Ta:Nb stoichiometry and crystal structure. Future work is directed at electro-optical characterization and to establish correlations between deposition and subsequent heat treatment with electro-optic properties. The work was presented by a graduate student in collaboration with ARL and the University of Oslo.

• Multi-Plane Light Conversion (MPLC) for Turbulence Mitigation (Poster). This project is tracking cutting-edge applied-light-processing research in academic and commercial laboratories. ARL tests of the COTS “TILBA” component have verified that bulk micro-optic Hermite-Gaussian decomposition followed by recombination in single-mode fibers can significantly mitigate turbulence. Detailed simulations predict that, in a properly designed system, this improvement can be accomplished with very low loss of optical power.

Meta Optics

The advent of metamaterials with hitherto unimaginable optical properties is revolutionizing the design of light-based systems, from cameras to PICs. This research focus is an excellent choice for ARL, and optical metamaterials appear in numerous photonics research projects in the core competency portfolio, many of which have been discussed above. Much of this work is very forward-looking, but ARL is beginning to make significant technological progress for communications and other applications.

• Advanced Nanoscale Fabrication Technologies for Meta-Optics and Integrated Photonic Devices (Poster). This poster showcased the ARL team’s fabrication expertise through strong prototyping, infrastructure, and tool utilization. Having staff with experience on prototyping electronic chips to quickly adapt to the new methods required for optical device fabrication has been a key resource for the meta-optics work (and PIC development) at ARL. The in-house fabrication capability has enabled the demonstration of fabrication techniques that can improve device performance as well as prototyping of novel photonic designs. For example, to generate smooth sidewalls for the on-chip photonic crystal lasers, the team utilized resist reflow and a combination of selective and non-selective etching. Additionally, the ability to fabricate the asymmetric metamaterial structures brought to life the theoretical work described in the paragraph above. The fabrication techniques utilized by the ARL team may be translatable and scalable to a foundry setting, especially through the use of deep ultraviolet lithography.

Optical Clocks and Timing

ARL is working at the forefront of efforts to measure and “distribute” time with extremely high accuracy using robust, compact, low-power optical devices. By keeping pace with main-line optical clock development efforts while engaging in other, more long-term and speculative research, this is a well-balanced aspect of the photonics core competency.

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⁵ J.R. Bickford, H.H. Sønsteby, N.A. Strnad, P.Y. Zavalij, and R.C. Hoffman, 2019, “Control of Potassium Tantalate Niobate Thin Film Crystal Phase and Orientation by Atomic Layer Deposition,” Journal of Vacuum Science and Technology A 37:020904.

• Epsilon Near Zero-Based Environmental Insensitive Cavity (Presentation). This presentation leverages ARL’s work on developing thick indium-tin-oxide (ITO) films for nonlinear nanophotonics applications. ITO has been shown to demonstrate large, wavelength-dependent optical nonlinearities that can be modulated by applied fields. Thick ITO layers with these properties could potentially be used to expand nonlinear nanophotonics applications to include new classes of optoelectronic devices, including air-core waveguides and integrated low-power electro-optic modulators. The team at ARL has advanced this line of study by developing wavelength-thick epsilon-near-zero ITO films, which is work that was published in Nature Scientific Reports in 2020.⁶ They have used this system to demonstrate a proof-of-concept air-core microresonator cavity with reduced thermal dependence on cavity resonance shifts over silicon by a factor of approximately 80 times.
• Study of Thermal Optical Coefficient for Enhanced Design of Anti-thermal Optical Devices (Poster). This project investigates novel approaches for tailoring materials in such a way as to make them insensitive to temperature changes. The stability of light propagation in optical systems is critical for applications that require precise and stable frequency performance. However, since the refractive index of optical materials is a function of temperature, innovation is required for the design and fabrication of temperature-insensitive resonators.

  The poster describes an alternative and much simpler approach for a temperature-insensitive cavity compared to the presentation “Epsilon Near Zero Based Environmental Insensitive Cavity.” It is based on the integration of Si/SiN_x/SiO₂-layered materials and the strategic inclusion of titanium dioxide (TiO₂) metamaterial. To demonstrate a proof of concept, simulations of 10 layers of Si/SiO₂ and Si/TiO₂ pair structures were performed. The simulations show that between 20°C and 60°C, the thermal shift transmission with the Si/SiO₂-paired structure is negligible. If this can be confirmed with experimental data, it would be a unique, and possibly world’s best, result.

• On-Chip Optical Frequency References (Demonstration). A notable highlight of the tour of ARL’s facilities was the “clock lab.” PIC-based optical frequency combs are used in many applications,⁷ but perhaps the most important is in stabilizing optical clocks. The ARL facility is excellently equipped with a top-of-the-line commercial frequency comb system that is being used to confirm the performance of devices designed and fabricated at (and for) ARL, one of which exhibited very good performance during the laboratory visit. The ARL team is well connected with both industry and academic groups developing optical comb PICs and has established collaborations to use the laboratory’s advanced equipment to measure the performance of devices and subsystems from other institutions. This allows ARL to stay abreast of developments in the field and benchmark the performance of its own frequency combs.

Radio Frequency Photonics

Very little detail was presented on the RF photonics research theme, however, there is some evidence that ARL is making good progress toward integrating optical delay-based phased-array steering and spectral analysis of microwave/RF beams.

• Chip-Scale RF-Photonic Phased-Array Antenna (Poster). This poster describes an optical chip implementation of the photonic beamforming architecture first demonstrated in fiber

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⁶ J.H. Ni., W.L. Sarney, A.C. Leff, J.P. Cahill, and W. Zhou, 2020, “Property Variation in Wavelength-Thick Epsilon-Near-Zero ITO Metafilm for Near IR Photonic Devices,” Scientific Reports 10:713.

⁷ H. Hu and L.K. Oxenløwe, 2021, “Chip-Based Optical Frequency Combs for High-Capacity Optical Communications,” Nanophotonics 10:1367–1385.

• optic form at ARL in 2016.⁸ This novel technique, in which a tunable laser feeds a serial array of wavelength-tunable slow-light waveguides (based on Bragg grating dispersion) results in a cascade of optical true time delays in a very compact structure, is a significant advantage over most other optical chip-based beamformer designs.
• Analog RF-Photonic Correlation Receiver - Single Pulse Spectrum Analyzer (Poster). This project has made steady progress toward practical realization of an ARL-patented photonic technology that uses analog processing to recover information from pulsed signals in near-real time.⁹ This is accomplished by mixing the incoming signal with optical pulses, and then performing a Fourier transform to recover the incoming signal. While claims in the group’s recent paper¹⁰ to have beaten the Heisenberg-Gabor limit may be debatable, the technique’s extremely high single-pulse spectral resolution is quite remarkable. Systems based on this approach can be used for spectral analysis, secure communications, and advanced radar systems.

Research Portfolio Opportunities

The compound semiconductor on insulator (CSOI) approach being pioneered by the Quantum Photonics Laboratory at the University of California, Santa Barbara, can enable the fabrication of devices that seamlessly integrate active optoelectronic components with traditional PIC structures on a single chip. By strengthening and expanding ARL’s already-established contact with this group,¹¹ CSOI technology could be brought in-house, giving it a powerful new tool for advancing the PICs program.

ARL’s interest in RF photonics and quantum technology could be enhanced by expanding it to include study of the entanglement of photons with radically different frequencies (i.e., microwave and optical). Work on this subject at the Institute of Science and Technology in Vienna is still in the laboratory demonstration stage but shows promise of rapid improvements that could ultimately impact many aspects of quantum engineering, including communications, sensing, and computing.¹²

If resources become available, ARL could consider initiating a program in high harmonic generation by ultrafast lasers.¹³ In addition to putting ARL at the forefront of atomic/molecular/optical physics research, this could bring to ARL an extremely useful tool for non-destructive 3D characterization of photonic and electronic chip structures and material composition.¹⁴

During the review, the Time and Frequency Laboratory at the Adelphi Laboratory Center was toured. So far, ARL’s work has mainly focused on developing microresonators and microcombs without integrating them with atoms to build frequency standards, so half of the picture needed for optical clock development has not yet been explored and may present an exciting area of collaboration between the

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⁸ W. Zhou, M. Stewad, S. Weiss, O. Okusaga, L. Jiang, S. Anderson, and Z.R. Huang, 2017, “Developing an Integrated Photonic System with a Simple Beamforming Architecture for Phased-Array Antennas,” Applied Optics 56:B5–B13.

⁹ M.-C. Li and W. Zhou, “Method and Apparatus for Analyzing the Spectrum of Radio-Frequency Signals Using a Fiber Optic Recirculation Loop,” U.S. Patent8861567B2, filed November 15, 2012, and issued October 14, 2014, https://patents.google.com/patent/US8861567B2/en.

¹⁰ W. Zhou, 2023, “Reaching the Frequency Resolution Limit in a Single-Shot Spectrum of an Ultra-Short Signal Pulse Using an Analog Optical Auto-Correlation Technique,” Journal of Lightwave Technology 41:114–119.

¹¹ J. Sun, 2024, “Advanced Nanoscale Fabrication Technologies for Meta-Optics and Integrated Photonic Devices,” DEVCOM ARL presentation to the committee, July 23.

¹² R. Sahu, L. Qui, W. Hease, G. Arnold, Y. Minoguchi, P. Rabl, and J.M. Fink, 2023, “Entangling Microwaves with Light,” Science 380:718–721.

¹³ J.G. Eden, 2004, “High-Order Harmonic Generation and Other Intense Optical Field-Matter Interactions: Review of Recent Experimental and Theoretical Advances,” Progress in Quantum Electronics 28:197–246.

¹⁴ M. Tanksalvala, C.L. Porter, Y. Esashi, B. Wang, N.W. Jenkins, Z. Zhang, G.P. Miley, et al., 2021, “Nondestructive, High-Resolution, Chemically Specific 3D Nanostructure Characterization Using Phase-Sensitive EUV Imaging Reflectometry,” Science Advances, https://doi.org/10.1126/sciadv.abd966.

photonics and quantum science competencies. The group could benefit from merging its work with atomic spectroscopy to build clocks and test the feasibility of the microresonators for stable and accurate timekeeping.

Additionally, there may be opportunities for the photonics core competency to work the biosynthesis and biomaterials core competency in the biological and biotechnology sciences competency to enhance aspects of protein structures for photonics applications.

Opportunities Identified for Individual Projects

Photonic Integrated Circuits

• Atomic Layer Deposition of KTa_xNb_(1–x)O₃ Thin Films for Silicon Photonics (Poster). Some challenges present in this poster are that KTN thin films are difficult to grow precisely and, as a result, the electro-optic properties of KTN thin films are currently limited compared to bulk KTN as reported for films grown by pulsed-laser deposition, which is not compatible with heterogeneous Si integration.¹⁵ Some risks associated with the project are that the material may not be controllable to get properties for an optical phased array. Additionally, the material has low Curie temperatures, and it would be ideal for the Curie temperature to be at room temperature.

  ARL is at an early stage in the electro-optical characterization of their ALD-grown KTN thin films, but with its solid research plan and systematic approach, ARL has a unique opportunity to lead the field in the heterogeneous integration of KTN for Si PICs. Additionally, it would be interesting to explore whether this material could be used for electro-optic phase shifters. Materials with high Kerr coefficients can also be used as microresonators for frequency combs.

• Multi-Plane Light Conversion (MPLC) for Turbulence Mitigation (Poster). ARL’s approach of replacing the single-mode fiber with a PIC-based beam combiner, and the multiple phase plates in the TILBA device with a monolithic structure will take a significant effort. However, it could lead to the creation of an extremely compact, low-SWAP “deturbulence” component for free-space optical (FSO) communication. Furthermore, accomplishing this could have implications far beyond free-space communications. Multistack “diffractive deep neural networks” are showing great promise for applications including image recognition and signal processing.¹⁶

Meta Optics

• Advanced Nanoscale Fabrication Technologies for Meta-Optics and Integrated Photonic Devices (Poster). ARL could facilitate progress in some of the extramural photonics projects; alternatively, the group may also be able to leverage extramural capabilities to develop new capabilities at ARL. In this respect, the collaboration with the University of California, Santa Barbara, on growing active compound semiconductors on the same substrate as silicon integrated optics is of particular importance. This unique capability can enable photolithographic fabrication of III-V sources and detectors directly on PICs, impacting virtually all of the other PIC-related work at ARL, AIM, and commercial PIC manufacturers.

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¹⁵ Y. Sakurai, X. Yuan, S. Kondo, M. Yoshino, and T. Yamada, 2022, “Optimizing the Growth of K(Ta_0.6Nb_0.4)O₃ Films Using Pulsed Laser Deposition and Their Electro-Optic Property,” Journal of the Ceramic Society of Japan 130:424–428.

¹⁶ Y. Li, M. Sadman, S. Rahman, and A. Ozcan. Optics & Photonics News, October 2024, p. 37.

Optical Clocks and Timing

• Study of Thermal Optical Coefficient for Enhanced Design of Anti-Thermal Optical Devices (Poster). The poster describes work that is at an early stage but shows promising simulation results. It should be relatively straightforward to fabricate the layered stack materials and experimentally confirm the simulations. While the layered stack may exhibit temperature insensitivity, the bandwidth may be limited and therefore it is worth investigating experimentally.
• Optical Positioning, Navigation, and Timing (PNT)—Transmit/Receive Unit with Active Retroreflector (Poster). Performing time transfer and data transmission optically will allow fielded nodes to perform PNT operations as well as communicate over channels without RF transmission, which can be easily detected in the field. This poster describes a small effort to develop FSO transceivers with an expanded field of view over existing approaches. The team is developing the optics and electronics required to simultaneously transmit and receive signals from the unit along the same optical axis with two geometries: one in which the transmitting fiber output is encircled by an array of photodiodes for detection and another in which a hole is drilled in the center of the photodiode for delivery of the transmitted light. So far, the team has performed time-of-flight measurements over a 50-m link using a passive retroreflector design. The novel part of the effort will be the development of the active reflector, which is planned to be based on metasurface optics. The design will allow the nodes to transmit data along the time-transfer link to identify the receiver and send other relevant communications. It should be noted that the “holey diode” approach for the transceiver could suffer from serious difficulties, including high dark current/noise caused by the hole fabrication process and, more importantly, almost-certain crosstalk caused by light in the fiber leaking into the diode. The active retroreflector part of the work appears to still be in the planning phase. The capabilities of the metasurfaces for processing the incoming signals will be an interesting part of the design. The team needs to push forward on this capability, and they might consider designing and implementing techniques to test and mitigate any crosstalk between incoming and outgoing signals. Simultaneously transmitting and detecting signals along the same beam path is common in standard time-transfer techniques, since reciprocal paths are required to reject noise acquired during transit along the beam path—this becomes a challenging problem when the nodes are moving.

RF Photonics

• Chip-Scale RF-Photonic Phased-Array Antenna (Poster). The poster describes work on an alternative use of integrated photonics to get phase delays in which microresonator circuits are used to select the time delay.¹⁷ Continuing work on this approach is encouraged, since adding a second tunable delay methodology would facilitate the development of a fully integrated two-dimensional beamformer—a very important achievement. This approach currently uses heat to control the switches, which can be hard to control in fully integrated devices and requires more power than nonlinear optical processes in nonlinear waveguides. The team may want to consider researching the use of active modulators that work on physical principles other than heat.
• Analog RF-Photonic Correlation Receiver—Single-Pulse Spectrum Analyzer (Poster). In terms of opportunities, it might be quite difficult to engineer an integrated-optic version of the fiber recirculation loop and delay line. However, this unique architecture’s performance

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¹⁷ S.-Y. Cho, S. Anderson, and W. Zhou, 2021, “Microresonator-Switch-Based Silicon-Photonic True-Time-Delay Beamforming Circuit for RF Phased-Array Antennas,” IEEE Research and Applications of Photonics in Defense Conference (RAPID), https://doi.org/10.1109/RAPID51799.2021.9521374.

• seems so good that its reliance on significant lengths of fiber could be ignored (as in, for example, fiber optic gyroscopes).

Quantum Science Core Competency

Accomplishments and Advancements

The quantum science core competency is funding world-class researchers and producing world-leading results. The team’s work is of high caliber, and the impact of several of their efforts is likely to produce high-impact results of great value to the community. It is very important to have a government team in this key research area. Quantum research in all program areas is currently an extremely hot topic owing to the National Quantum Initiative.¹⁸ as well as advances and investments made in industry. The field, however, is suffering from being over-hyped across the board. It is therefore critical to have a government team (or teams) that fundamentally understands the underlying science and technologies and can serve as an honest broker in conversations with administrators regarding the capabilities of quantum technologies. ARL can ensure it maintains an honest broker position within the community by continuing research efforts and allowing its government team to interact with the community through presentations, panel sessions, and so on to provide honest assessments.

The quantum science core competency overview began with the presentations “Extramural Quantum Information Science (QIS) Program” and the “Extramural Atomic and Molecular Physics (AMP) Program,” which highlighted the extramural research program. The extramural program—incorporating studies of clocks, strong correlations in quantum systems, and quantum materials—is coherent and well thought out with a mix of theory and experiment. It is at the very forefront of quantum science and producing exciting results that are generating much interest within the community and keeping the United States at the forefront of these fields. The PSQs presented in each portfolio were well constructed and judiciously addressed the most pressing research challenges facing the community. The thoughtfulness of the PSQs speaks to the team’s understanding of the research community and is a testament to their knowledge of the work going on across the world. The questions address some of the most pressing challenges the research community is facing.

The QIS program presented results on novel molecular ion work, which may offer new tools for state preparation and readout in molecular ions for quantum simulations and computing. The inability to effectively perform state preparation and readout in molecular ion systems is a current limiting factor, and so this research may provide a significant advance. The team also highlighted novel control and manipulation toward scaling qubit systems. This “spectator” qubit technique was so effective that a neutral atom group started using it and recently published an article in Science magazine that translated the technique into a neutral atom array.¹⁹

The AMP program highlighted work on laser probing of a nuclear transition in thorium-229, which represents the culmination of over a decade of hard work and investment in a high-risk, high-reward technology that has paid off. This has been featured at several recent atomic physics conferences and is exciting as it opens the possibility of developing a solid-state nuclear clock that holds promise for being protected from the environment. The extramural clock work is also at the cutting edge with studies of array clocks with long coherence times and the possibility of exploiting squeezing techniques and multiplexed atomic clocks. The team also highlighted the first demonstration of atom squeezing in a neutral atom clock array probed differentially to remove laser noise. Squeezing allows the same amount of precision in a shorter averaging time. Ultimately, using Greenberger–Horne–Zeillinger (GHZ) entangled states in an atomic clock array may allow one to reach the Heisenberg limit.

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¹⁸ See the National Quantum Initiative website at https://www.quantum.gov, accessed October 23, 2024.

¹⁹ K. Singh, C.E. Bradley, S. Anand, V. Ramesh, R. White, and H. Bernien, 2023, “Mid-Circuit Correction of Correlated Phase Errors Using and Array of Spectator Qubits,” Science 380:1265–1269.

Overall, the team is closing outstanding research gaps, supporting opportunities that push topics in unexpected directions, and facilitating community-building to bring together researchers across qubit platforms (through Multidisciplinary University Research Initiative programs) to innovate new methods to address common challenges in qubit control. The program in quantum simulation for understanding new materials is a hot topic, and the work is again at the forefront of research in this area.

The intramural quantum science program is also of the highest quality. The team presented an overview of the Intramural Quantum Science and Technology Program that was well motivated and provided insight into why they chose the research directions that were highlighted. The goals motivating the intramural program showcase the team’s understanding of the depth and breadth of the research community and highlight some of the most pressing issues facing the community regarding quantum sensors.

The first research presentation centered on solid-state quantum sensors using NV centers in diamond. The team utilized strong coupling between a dielectric microwave resonator and an ensemble of NV centers at room temperature to enhance optical readout. The microwave-cavity-coupled NV magnetometer has sub-picotesla sensitivity and corresponds to the best sensitivity demonstrated for NV magnetometry based on continuous-wave optically detected magnetic resonance (CW-OMDR). The cavity quantum electrodynamics (cavity-QED) approach is promising in achieving the sensitivity needed for applications in magnetic navigation, in which solid-state spins offer potential advantages over their atomic counterparts for providing spatially resolved vector information referenced to the crystal orientation, integrability, and miniaturizability.

The team presented two supporting posters, “Fiber Quantum Magnetometry with NV Centers in Diamond” and “All-in-One Quantum Diamond Microscope for Sensor Characterization.” The former is aimed to further reduce the SWaP by coupling NV diamonds to eliminate the need for bulky optics. The latter poster focused on the design and demonstration of a wide-field microscope to characterize the optical, strain, and spin properties of the diamond crystal and its quantum emitters in a high-throughput manner. This capability adds to the team’s ability to develop viable diamond sensors and is worthwhile to adapt it to other material systems (including silicon carbide [SiC], which is being worked on). Overall, the intramural effort has established strong collaborations with academic partners who are leaders in the field to push forward their research.

ARL’s intramural research in Rydberg sensing of RF microwave radiation is a world-leading effort. The research team was the first to demonstrate the feasibility of such sensing with its promise of designing compact sensors with a broad frequency response limited only by quantum rather than thermal noise. The group has continued to push Rydberg sensors toward practical use cases by utilizing heterodyne techniques to demonstrate the ability to receive multiple frequencies simultaneously. Other advances promise the detection of the polarization of incoming waves and location of their source. Notably, during discussions at the poster session, it became evident that they are supporting collaborations with industry and other partners pushing toward developing lower SWaP packaging to allow introduction of this technology in the field. The presentation explored some of the fundamental research possible with Rydberg sensors and demonstrated satellite radio detection, the simultaneous detection of several microwave frequencies, and the possibility of identifying the direction of an incoming wave. It should be noted that the team recently published a Journal of Physics B article²⁰ that presents an honest assessment of the current Rydberg atom sensor capabilities, and this is an asset to the research community to help level-set the capabilities of the technology.

The team presented their efforts on establishing a SiC foundry at the Adelphi Laboratory Center. The foundation of this facility was initiated in 2016 and is just starting to produce results due to supply-chain issues and other delays. However, the SiC reactor is now up and running and starting to produce samples for both the intramural researchers at ARL and the broader research community. This is an important capability in the context of developing new defect-based sensors. The availability of a state-of-

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²⁰ D.H. Meyer, Z.A. Castillo, K.C. Cox, and P.D. Kunz, 2020, “Assessment of Rydberg Atoms for Wideband Electric Field Sensing,” Journal of Physics B: Atomic, Molecular and Optical Physics 53:034001.

the-art, well-characterized source for SiC films will close a gap in the current U.S. capability, and the availability of high-quality thick films will be of great scientific value to the Department of the Army, the greater DoD, and the larger research community. It is highly encouraged that the SiC growth capability be widely advertised to the communities of interest and coordinated with other government-funded quantum foundries funded under the National Quantum Initiative.

The final topic presented was the poster “Long-Baseline Entanglement Distribution Between Trapped-Ion Quantum Processors,” with a plan for trapped-ion quantum networking focusing on long-baseline entanglement distribution between trapped-ion quantum processors. This is a smaller effort tackling challenges that would be of high benefit to the larger trapped-ion community. The team is working toward a demonstration of using telecommunication frequencies within ytterbium-trapped ions to network distance quantum nodes over a telecommunication channel. The team is exploring novel approaches to cryogenic ion traps interfaced with optical cavities with the ultimate goal of entangling two remotely trapped ion modules using 1650 nm radiation. If successful, this effort will provide significant advances in both telecommunication quantum channels and new ways to integrate cavities into trapped ion quantum nodes.

Speaking more broadly, the quantum science core competency team demonstrated a clear understanding of the underlying science through presentations, laboratory tours, and related conversations. This is further evidenced by the good mix of complementary theory and experiment across the portfolio. They have a clear understanding of the research being conducted elsewhere through their connections to extramural leading world-class research groups. The offsite ARL facilities also allow the teams to attract and retain top talent. The significance of these remote research sites is clear, and they need to be maintained to the highest degree possible. The inter-relationships between the extramural and intramural efforts are exemplary, and the team highlighted the strong connections across the groups. The extramural and intramural teams are encouraged to maintain coherence and high-quality programs and ensure the connections between the two organizations stay strong. It is important to note that the team is also well connected across the government and is participating in several White House Office of Science and Technology Interagency Quantum Working Groups.

The quantum science core competency research portfolio also displayed sound research methods and methodologies. Many of the talks and posters provided discussion on the reason behind the chosen technology and included the underlying theory, modeling, and simulations required to analyze the anticipated experimental data. A notable example of this is the Rydiqule software to model Rydberg sensor response to arbitrary input fields. This was developed under a DARPA effort, and the team is sharing it with the wider community soon.²¹ So far, they have shared it with research collaborators and partners.

Finally, the quantum science core competency portfolio is well balanced. As described, the team is leading in the Rydberg sensor area and growing several solid-state efforts (diamond and SiC). The Rydberg sensor effort needs to be maintained or expanded. For the smaller research efforts (trapped-ion quantum networking and SiC), ARL will need to decide whether these should be future growth areas. ARL’s work on solid-state sensors is laudable. These hold great promise toward being deployable, and there are fewer efforts in this area in academia as compared to their atomic counterparts. This may be a research area to expand in the future. The team has invested in several cutting-edge research areas, and through their scientific depth, breadth, and close connections with the extramural managers and collaborators, have made sound decisions for pursuing novel research areas.

Research Portfolio Opportunities

Through the intramural research program, ARL is doing an excellent job forming partnerships with key research groups and industry partners; however, there may be an opportunity to enhance collaborations with the other core competencies within the photonics, electronics, and quantum sciences competency portfolio. There seemed to be a lack of discussion between some of the competency areas—a

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²¹ See the Rydiqule website at https://rydiqule.readthedocs.io/en/latest, accessed October 23, 2024.

notable example is there appeared to be limited to no conversations between the sensing and quantum science groups. There may be some early opportunities for the quantum team to field some of their more advanced sensors with the sensor core competency, or, at the very least, learn from them what are the largest impediments to operating in a field environment.

Another opportunity that the intramural group is trying to push toward is a closer collaboration between the photonics group and the quantum science groups. A metasurfaces researcher dedicated to strengthening this collaboration could be an important addition. Due to the significant in-house expertise in fabrication, photonics, and quantum science, such an individual could help ARL to become a world leader in the interconnection of photonics and atomic and solid-state quantum systems.

A recurring challenge vocalized across the teams was the inability to easily publicize their work. New guidance has greatly restricted the teams’ ability to highlight research results through press releases and related activities. It is very important to be able to do this especially at a DoD laboratory. This is severely impacting the groups’ ability to maintain collaborations with other world-leading groups. A more widespread dissemination of the exciting research under way in the ARL would help in recruiting top talent to ARL.

Sensing Core Competency

Accomplishments and Advancements

Through oral and poster presentations as well as visits to the laboratories, a great deal of information was made available during the review that highlighted the core competency’s ongoing research in sensing platforms. ARL’s demonstrations were quite impressive, and many projects evinced high-quality, innovative work that were grounded by strong research approaches or methodologies. The research was state of the art and is at par with (or exceeded) the work going on elsewhere.

The extramural program is largely focused on leading-edge work aimed at improving the performance of infrared/visible sensors. This is an extremely diverse field, and the decision to concentrate on a few promising material systems and device concepts is a good one. The academic groups selected for this work are reasonably well respected. ARL may consider connecting with researchers at the University of Arizona whose work appears to compliment current extramural efforts.

Particular highlights of ARL’s intramural program include very significant improvements in micrelectromechanical systems (MEMS) inertial sensor performance and notable progress on fusing data from distributed networks of disparate sensor types. ARL is also doing important work that is not quite as advanced as its MEMS work on tracking targets using electro-optical (EO)/infrared/visual data, and on acoustic (wind) noise reduction.

ARL is developing MEMS-based inertial sensors for GPS-denied navigation. Its research in this area focuses on improving C-SWaP, sensor noise, and bias stability. ARL has a strong team working to address critical problems in MEMS-based rotation sensing toward these goals and has developed notable capabilities in the design and fabrication of MEMS materials that can be leveraged for other sensing applications such as acoustic sensing. ARL’s team is working on solving problems to improve the performance of MEMS sensors and develop new applications. The team maintains collaborations with other leading interdisciplinary MEMS researchers—for example, at the University of California, Irvine, and at the University of Maryland.

ARL’s impressive demonstrations reflected work in this area that is state of the art. Specific commentary on the individual strengths of two of these projects include the following:

• Augmenting UAS Datasets with Synthetic Data for Training Onboard Perception Algorithms (Poster). It is widely known that in many applications, available data are insufficient for training models. In such situations, it is desirable to be able to generate synthetic data that augments the real data set and can be used for training purposes. Unfortunately, the poster did not provide a problem statement, or communication about the

• scientific significance and novelty of the work, which made the research difficult to assess. What is clear, however, is that this and other similar data sets are necessary to test new algorithms or train new models. In that sense, this is enabling technology that is useful to advance the state of the art in modeling and algorithm development.
• Quality Factor Tuning of Quad Mass Gyroscopes (Presentation). This presentation showed results from a large project that included intramural work, SBIRs, cooperative research and development agreements with large defense contractors, and collaborations with other Army research centers. Through this project, the ARL team demonstrated state-of-the-art angle random walk results for MEMS gyroscopes, showing a reduction by a factor of six in noise for their quadrupole-mass gyroscopes over other comparable MEMS approaches. They accomplished these noise improvements through the use of in-house, high-quality piezoelectric materials that significantly improved quality-factor tuning (Q-tuning), leveraging the maturity of design and fabrication process in a Si-only platform, meticulous redesign of multiple sensor elements aimed at reducing nonlinear transduction mechanisms, and through an improvement in vacuum packaging. The team has also shown a path to improve device bias instability by over a factor of 20 with mechanical equalization and stabilization of the quadruple resonator quality factors using tuning methods that have been developed at ARL. They have recently published these results at the IEEE International Symposium on Inertial Sensors and Systems as well as in the IEEE Journal of Micrelectromechanical Systems, which are among the top conferences and journals in this field. The team has shown strength in fabrication, theory, and materials and are leading in these research areas.

Research Portfolio Opportunities

The assessment criteria asked for opportunities, if found, within the competency where improved direction, increased focus, connections with other research lines, or other changes could better and more quickly address the competency objectives. There is much to be gained by developing a broader understanding of extramural research and enhancing external engagements in the areas of multi-modal information fusion and AI/ML applications to sensing and fusion. ARL could also look at the latest methods for processing data generated by acoustic, seismic modalities and better incorporate ML. An example of an individual who may be helpful is Florian Meyer as well as researchers at the University of Connecticut, which include Peter Willet and Yaakov Bar-Shalom.

Additionally, since the eventual applications of some of the sensing modalities will involve humans in the loop, it will be important to ensure human factors researchers are engaged. Thus there is an opportunity for the humans in complex systems competency to work with the sensor core competency. Early collaborations with them will be helpful, especially in the case of technologies that will reach eventual transition. Additionally, it was noted that the material provided during the assessment did not mention ongoing work on the science of fusion. As additional sensing modalities are added, it becomes imperative that optimal/suboptimal fusion is carried out for tasks such as detection, localization, and tracking. Once detections and tracks are available, some inferences on the overall situational awareness for the region of interest need to be made. This would include intent, war-gaming strategies, resource management etc. This latter part is likely to require collaboration with other ARL competencies.

On another note, there appears to be substantial overlap with the work in military information systems competency—including a research focus on networks of fixed and mobile sensor systems. It could be beneficial for these groups to communicate and possibly collaborate if they are not already doing so.

Of interest to ARL groups working on the detection and identification of personnel and their casualty/mortality status may be the work of the Zalevsky group at Bar Ilan University in Israel, which has developed the ability to detect the health status of humans at distances of 70 m or more.²²

Given the competency’s ongoing activity in opto-acoustics and quantum phenomena, it might also be helpful for ARL to connect with the Kippenberg group at EPFL (Swiss Federal Institute of Technology in Lausanne),²³ as this group may have complementary research interests.

Opportunities Identified for Individual Projects

The following individual project opportunities were identified:

• Human Agent Interaction for Intelligent Squad Weapons. This project aims to employ the information that may be collected via intelligent squad weapons for enhanced target acquisition and situational awareness. This is an innovative way to collect surveillance data as individual objects are on the move, and then fuse it in real-time to improve situational awareness. This system is fairly mature but can always be made smarter. The networking of sensing platforms carried by multiple objects would yield improved situational awareness over a wider region and also alleviate the impact of obstructions and occlusions.
• Target Tracking with Unattended Ground Sensors. This project focused on the problem of inferring the target tracks moving through a sensor field. This is very interesting work. Leveraging contextual information is certainly valuable. The proceedings of the International Society on Information Fusion’s fusion conferences contain several papers relevant to this research. One author whose work may have synergies with this project is Florian Meyer of the University of California, San Diego. In addition, it will be important to establish the novelty of the work. Otherwise, it will be considered as an implementation of a known approach, and implementing known algorithms is not advancing the state of the art. Perhaps the novelty is the use of two different types of sensors, acoustic and seismic, or maybe the novelty is having multiple targets.

PORTFOLIO OF SCIENTIFIC EXPERTISE

Electronics Core Competency

ARL has a strong set of capable intramural and extramural scientists supporting the electronics core competency. ARL may consider leveraging its extramural research partners to help accelerate some of the intramural device-level research. For example, consulting with circuit designers with expertise in building polarization imagers (e.g., individuals like Viktor Gruev at the University of Illinois Urbana-Champaign) would complement the ARL polarization imager effort. As previously mentioned, adding more IC analog design expertise through more extramural collaborations could also be helpful to help build those capabilities and bring them in-house.

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²² See, for example, N. Ozana, I. Margalith, Y. Beiderman, M. Kunin, G. Abebe Campino, R. Gerasi, J. Garcia, V. Mico, and Z. Zalevsky, 2015, “Demonstration of Remote Optical Measurement Configuration That Correlates With Breathing, Heart Rate, Pulse Pressure, Blood Coagulation, and Blood Oxygenation,” Proceedings of the IEEE 103:248–262.

²³ M. Chegnizadeh, M. Scigliuzzo, A. Youssefi, S. Kono, E. Guzovskii, and T.J. Kippenberg, 2024, “Quantum Collective Motion of Macroscopic Mechanical Oscillators,” Science 386(6725):1383.

Photonics Core Competency

Concerning the photonics core competency, it can be noted that photonics is a vast field with a surfeit of opportunities to perform forefront research. ARL has not attempted to cover this entire field, but instead has built an impressive program by focusing on a few key areas and recruiting and maintaining top-notch scientists and engineers to work in those areas. As a result, there is no doubt that ARL photonics researchers are able to compete and collaborate at a very high level with world leaders in the design and fabrication of optical chips, optical clock development, microwave photonics, and in the development and use of optical metamaterials.

Quantum Science Core Competency

The intramural and extramural research teams supporting the quantum science core competency are both excellent as highlighted in the “Advancements and Achievements” section of the core competency. ARL has built an exceptional intramural and extramural research team. As previously mentioned, the quality of the PSQs speaks to the team’s understanding of the research community and is a testament to their knowledge of the work going on across the world, as these questions address some of the most pressing challenges the research community is facing.

As previously mentioned, there could be a closer collaboration between the photonics group and the quantum science groups, and a metasurfaces researcher could help to bridge the two fields. This will help to facilitate ARL becoming a world leader in the interconnection of photonics and atomic and solid-state quantum systems. Additionally, there did not appear to be much collaboration between the classical sensor and quantum sensor teams within the photonics, electronics, and quantum sciences competency, and these two teams can increase communication to facilitate greater cross-pollination.

Another potential challenge is the risk of not adequately resourcing some of the smaller research efforts. ARL has spent significant time and resources to develop a SiC foundry capability, but the team reported that only a handful of researchers were involved, and some were more temporary students and interns. There are few (if any) university or national laboratories currently engaged in SiC materials research. The ARL SiC foundry is in a unique position to research the materials growth, characterization and devices for novel applications, ARL will need to be careful that utilization of this important DoD resource does not suffer longer delays due to lack of resources. It was also noted that the trapped-ion quantum networking effort was fairly small. This is a critical research area, and ARL will want to ensure that the resources are adequate to meet its goals.

Sensing Core Competency

The ARL scientists supporting the sensing core competency were very impressive. They showed both interest and passion for their research. Several of them have completed their doctoral programs, while a few are currently pursuing their doctoral degrees. To make rapid progress, the sensing core competency can use a few additional people with expertise in AI/ML, information fusion, collaboration in multi-agent systems, and human factors. Some of this expertise is available in other ARL competency areas (e.g., the humans in complex systems core competency and the network, cyber, and computational sciences core competency), and closer collaboration with them is suggested. These competencies may also assist with sensor integration, data training and developing algorithms and training models for deep sensing. Additionally, while there was evidence of some extramural efforts in the sensing area, more extramural engagements could be undertaken.

FACILITIES AND RESOURCES

Electronics Core Competency

In contrast to the other core competencies, which had facilities tours as part of the review agenda, the electronics core competency facilities were not toured, rather, they were described through presentations. These facilities and resources supporting the electronics core competency were sufficient, and there are no concerns in this regard.

Photonics Core Competency

Although the evaluation team had a very limited glimpse of the facilities supporting the photonics core competency, what was seen appeared to be very good, and in some cases excellent. During the review, the Time and Frequency Laboratory at the Adelphi Laboratory Center was toured. In addition to developing the infrastructure needed for low SWaP-C optical clocks, ARL has a strong team working on the underlying fundamentals of microresonator-based frequency combs that are well connected to research in the field at other institutions (e.g., California Institute of Technology and the National Institute of Standards and Technology). In fact, the ARL laboratory is so well equipped that several of these use the laboratory’s advanced capabilities to measure the performance of their own devices and subsystems. This work is essential for optical clock development and useful for other microresonator research areas that are under way at ARL, including optical delay lines, phased array antennas, and RF photonics beamforming and steering.

The team is using an onsite fabrication laboratory for early prototyping and process development of optical chips, and the AIM Photonics Foundry for the fabrication of fully integrated large-scale devices. This is a significant advantage for the group and also serves the broader community by developing a capability that can be used by other researchers across the government, academia, and in industry. This has allowed the team to form valuable collaborations with other external laboratories. Because some of the areas of ARL photonics research are not as focused on publications and conference presentations, the informal networks formed through these collaborations seems to be one of the best ways ARL has of attracting new talent.

As previously mentioned, the CSOI approach being pioneered by the Quantum Photonics Laboratory at the University of California, Santa Barbara, can enable the fabrication of devices that seamlessly integrate active optoelectronic components with traditional PIC structures on a single chip. By strengthening and expanding ARL’s already-established contact with this group, CSOI technology could be brought in-house, giving it a powerful new tool for advancing the PIC program.

Quantum Sciences Core Competency

The research facilities supporting the quantum sciences core competency are of high quality. The laboratories are well equipped with up-to-date equipment and facilities. The in-house ARL laboratories are complemented and strengthened by the offsite remote facilities (Massachusetts Institute of Technology and University of Texas at Austin, etc.). One notable recent change is the closing of ARL’s Open Campus facility. This Open Campus allowed ARL to bring in leading international researchers and provided a venue to bring the best in the world to discuss the most challenging research problems.

During the review, a few researchers noted the drawbacks to closing the Open Campus facility, because it allowed the potential to bring world-class researchers onsite to work with ARL research teams. When the Open Campus launched, it caught the attention of other DoD laboratories and inspired another DoD laboratory to open its own open campus, which is successfully operating. The ARL team expressed interest in revisiting the Open Campus capability at ARL. Although ARL does have access to several offsite campuses, the proximity of the Open Campus to the ARL in-house research teams allowed ARL to

have in-person research exchanges and discussions that can be particularly fruitful and identify novel future research opportunities. This is currently a missing component in its main facility.

Sensing Core Competency

During the assessment, two facilities were toured to show the onsite intramural resources and technologies for the sensing core competency. The first facility focused on sensors and gyroscopes, and the second facility focused on fusion and the Deep Autonomous Reconnaissance and Targeting Sensing program. These facilities include the sensor fabrication facility, which has a clean room; and the sensor hardware design and testing facility, which has an anechoic chamber. Both are well equipped and state of the art. It is not clear, however, if there is adequate technician support available. If there is limited support, then adding technicians may help to facilitate rapid progress.