There are many common media narratives of a single driven scientist having their "eureka!" moment and changing the world. However, the reality is that most groundbreaking science is a team effort. Bringing researchers together from different institutions, diverse backgrounds, and varied scientific interests enables new ideas and perspectives to flourish, problems to get solved, and science to progress. With these goals in mind, the U.S. Department of Energy's (DOE) Brookhaven National Laboratory encourages strategic partnerships with external institutions. An excellent example stemmed from a growing partnership with Howard University and Brookhaven Lab. In addition to creating research opportunities for scientists, faculty, and students at Howard, this partnership has resulted in external funding for their endeavors.
Tina Brower-Thomas of Howard University and Kenneth Evans-Lutterodt of Brookhaven Lab's National Synchrotron Light Source II (NSLS-II), a DOE Office of Science User Facility, were recently awarded a $1.5 million grant through the Department of Defense's University Instrumentation Program (DURIP), sponsored by the Office of Naval Research. With this funding, they will set up a research program to study the growth of perfect diamond thin films for quantum information systems (QIS). Brower-Thomas, Evans-Lutterodt, and their collaborators at Brookhaven and Howard are poised to make significant strides in growing this material, which shows promise in applications like quantum computing, communications, and sensing.
"The Office of Naval Research has a keen interest in developing and maintaining secure communications and networking," explained Brower-Thomas. "Some of the unique properties of diamond have made it one of the most promising candidates for implementing qubits, the way quantum information is stored, and other quantum technologies. Diamond of highest quality is essential for the development of secure communications and networking. Some of these unique diamond properties could also be used to make extremely sensitive magnetometers that may detect magnetic disturbances created by unfriendly submarines."
The Power of Partnership
Brower-Thomas is the executive director for the Center Integrated Quantum Materials (CIQM) at Howard University and supports the materials thrust in the Brookhaven-led Co-Design Center for Quantum Advantage (C2QA). With an expertise in quantum materials, she has had ambitions to build on the materials science legacy at Howard University, her undergraduate alma mater. With this funding, she looks forward to contributing to their capacity to grow quantum materials.
Kenneth Evans-Lutterodt, her co-principal-investigator (co-PI) on this project, is a staff scientist at NSLS-II's In situ and Resonant Hard X-ray Studies (ISR) beamline. One of his research interests is using x-rays to study the growth processes of different materials in-situ with x-ray diffraction.
By leveraging resources from Howard, C2QA, the ISR beamline, and DURIP, the research team, led by Brower-Thomas and Evans-Lutterodt, now have the opportunity to explore growth methods that produce diamond with properties optimized for quantum applications.
"A defect-free diamond contains only carbon atoms in its crystalline structure," explained Brower-Thomas, "however, when there are missing carbon atoms or impurity atoms present in diamond, things start to get interesting for those in the field of quantum information science. These defects can be used to store bits of quantum information. For example, negatively charged nitrogen-vacancy (NV) is one of the most studied defects in diamond. In this defect's structure, a nitrogen atom sits next to a missing carbon atom. This structure is able to maintain a quantum state with a coherence time of more than a millisecond at room temperature. This may not sound like a long time, but in comparison with many other types of defects being explored as quantum bit (qubit) candidates, this is a significant improvement in lifetime."
To enable the longest coherence times, however, the highest quality of diamond material is needed as a host for the NV center.
"It has been shown that strain, deformation due to stress, in the diamond around the NV center negatively affects the lifetime of the quantum states," explained Evans-Lutterodt. "The ability to produce high-quality, strain-free diamond films, however, should lead to better qubit performance."
QIS isn't the only promising field for this technology. When NV centers in diamond interact with a magnetic field, optical properties change in a detectable way. The NV center is extremely sensitive to magnetic fields and can measure the spatial variation of magnetic fields on the nanoscale. Brower-Thomas is interested in collaborating with groups that build nanoscale magnetometers, instruments used to measure magnetic fields, using this type of diamond color center.
To fabricate, study, and improve the performance of color centers for these applications, Brower-Thomas must not only grow perfect diamond but also must be able to monitor the quality of these films on the atomic scale. The ideal technique for this is x-ray diffraction, a research method that measures how the x-rays scatter as they pass through a crystalline material in order to learn about its structure. Using the ISR beamline, Evans-Lutterodt is able to investigate the growth of novel materials through various x-ray scattering techniques.
"ISR is well suited to the special challenges of studying diamond growth," said Evans-Lutterodt. "The beamline has been successfully used to study growth in other challenging materials systems. Quantum grade diamond growth occurs in a hot plasma environment that is hostile to most of the traditional diagnostics that can provide real-time information on a growing interface. The sample temperatures are on the order of 1,000 degrees centigrade. The most important advantage of using x-rays is that they are relatively unaffected by sample growth environments like the temperatures required here. We hope that these advantages will allow the ISR beamline to contribute new knowledge to this field."
The Power of Persistence
Growing and characterizing quantum grade diamond requires specialized equipment, but neither Howard nor Brookhaven had all the critical pieces of equipment necessary. Brower-Thomas and Evans-Lutterodt plan to grow their diamond using a technique called microwave plasma chemical vapor deposition (MPCVD). MPCVD reactors are tools that use hot plasma to create a mixture of hydrocarbon radicals and ions that can result in diamond growth on suitable substrates.
To obtain the necessary resources, the team collaborated remotely in 2020 during the COVID-19 pandemic in order to write a proposal for funding. During this period, covid restrictions limited in-person experimental activity at NSLS-II, which gave both of them the time to focus on writing research proposals. Brower-Thomas was interested in the QIS applications of diamond material and Evans-Lutterodt wanted to dig deeper into fundamental issues of the diamond growth process, which are unresolved due to lack of adequate in-situ diagnostics of the growing interface.
The pair submitted their first proposal to funding agencies in 2020 but was not successful. This didn't deter the team though. Despite the initial setback, they found ways to communicate their goals more effectively. Tina reached out to colleagues at Howard and broadened the skill base of the team before making a second attempt.
"This time, we placed greater emphasis on the applications that would be of interest to the Department of Defense," said Brower-Thomas. "After making these changes, the second submission in 2021 was successful and the effort is now sponsored by the Office of Naval Research. The $1.5 million funding will support two MPCVD reactors, one installed at Howard University and the other designed to be compatible with the ISR beamline at NSLS-II."
As they began to embark on this research, Brower-Thomas applied to the 2023 spring session of the Visiting Faculty Program (VFP) at Brookhaven, a program that provides selected college faculty members the opportunity to collaborate with scientific and engineering staff on a project of mutual interest. With Evans-Lutterodt as her host, they were able to focus on laying the groundwork for this project. VFP was not the only partnership that helped drive Brower-Thomas' QIS research further.
"Research collaborations like CIQM and C2QA are essential to broadening participation in STEM," she remarked. "I have learned a lot from having a seat at the table and participating in research centers that are inclusive. They have opened the door to research in quantum materials and are a big part of my success."
Along with her co-PIs from Howard-Samaresh Guchhait and Pratibha Dev-Brower-Thomas intends to introduce the techniques and skills needed for crystal growth to a cohort of students during the first phase of the project at Howard before travelling to NSLS-II for the characterization phase. She aims to use this opportunity as a way to contribute to the current quantum revolution by preparing the next generation of quantum researchers.
By making the MPCVD reactor part of Howard's infrastructure, it can be used by faculty and students to gain a broad understanding of material properties. It will be a valuable asset to students that are a part of the Karsh STEM Scholars Program, a scholarship program through Howard for exemplary high school students. These scholars who are offered full scholarships are committed to pursuing either a Ph.D. in a STEM field or a combined MD/Ph.D. The MWPCVD will be used during Karsh STEM Scholars enrichment activities with the researchers tied to this grant providing mentorship.
"Howard University is among the largest producers of African American doctorate recipients of any university and is the only historically black university ranked tier-one of national universities," said Brower-Thomas. "This effort will be a beacon to the Howard community and will encourage participation in the field. The faculty supported by this effort will be empowered to support Howard's mission to train and prepare students for further education and a career in STEM."
"Research into quantum materials is expensive, and the necessary tools are highly specialized," explained Evans-Lutterodt. "To achieve state of the art research and make it accessible, we need to foster these partnerships. In some cases, the necessary resources only exist in a handful of places throughout the world. I hope that more people realize that access to facilities like NSLS-II is not out of reach and that they can take advantage of programs like the VFP."