From The DOE’s Lawrence Berkeley National Laboratory: “Boron Nitride with a Twist Could Lead to New Way to Make Qubits”
From The DOE’s Lawrence Berkeley National Laboratory
10.6.22
Rachel Berkowitz
Easy control over bright emissions from the crystalline material offer a route toward scalable quantum computing and sensing.
Shaul Aloni, Cong Su, Alex Zettl, and Steven Louie at the Molecular Foundry. The researchers synthesized a device made from twisted layers of hexagonal boron nitride with color centers that can be switched on and off with a simple switch. (Credit: Marilyn Sargent/Berkeley Lab)
Achieving scalability in quantum processors, sensors, and networks requires novel devices that are easily manipulated between two quantum states. A team led by researchers from the Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) has now developed a method, using a solid-state “twisted” crystalline layered material, which gives rise to tiny light-emitting points called color centers. These color centers can be switched on and off with the simple application of an external voltage.
“This is a first step toward a color center device that engineers could build or adapt into real quantum systems,” said Shaul Aloni, a staff scientist at Berkeley Lab’s Molecular Foundry [below], who co-led the study. The work is detailed in the journal Nature Materials [below].
For example, the research could lead to a new way to make quantum bits, or qubits, which encode information in quantum computers.
Color centers are microscopic defects in a crystal, such as diamond, that usually emit bright and stable light of specific color when struck with laser or other energy source such as an electron beam. Their integration with waveguides, devices that guide light, can connect operations across a quantum processor. Several years ago researchers discovered that color centers in a synthesized material called hexagonal boron nitride (hBN), which is commonly used as a lubricant or additive for paints and cosmetics, emitted even brighter colors than color centers in diamond. But engineers have struggled to use the material in applications because producing the defects at a determined location is difficult, and they lacked a reliable way to switch the color centers on and off.
The Berkeley Lab team now solves these problems. Cong Su, a postdoc from the research group led by Alex Zettl, a faculty senior scientist at Berkeley Lab and professor of physics at UC Berkeley, examined how color centers behaved in different sophisticated forms of hBN. The researchers found that two stacked and twisted layers of the material resulted in the activation and enhancement of ultraviolet (UV) emission from a color center, which can be shut off when a voltage is applied across the structure. “It’s like a sandwich with two pieces of bread, but one rotated relative to the other,” said Zettl. The rotation between the two layers activates the color centers at the interface to become extremely bright. The applied voltage then easily and reversibly tunes the intensity from bright to completely dark, without “unrotating” the halves.
An electron beam placed at a series of locations on a sheet of twisted hBN intensifies the light emission from each location. The brightness depends on how long the beam sits at a given point, or the electron flux delivered to that point. The result is an illuminated pattern. (Credit: Su et al. 2022)
Aloni’s development of a modified electron microscope that not only probed the material’s structure but also collected the emitted light for analysis turned out to be key for this study. The setup uses an electron beam to excite the color centers; the researchers also found that they could use the electron beam to activate color centers and draw patterns, such as a smiley face, onto hBN. “People typically zap the material with lasers or ions, but we’ve instead zapped it with a beam of electrons,” said Zettl.
The study achieves three steps toward realization of a scalable quantum device. First, the UV color centers in hBN can be reliably activated to exceptional maximum brightness, by twisting the crystal interface. Second, these color centers can then be gradually and reversibly dimmed by a simple applied voltage. Finally, electron beam treatment allows further precise spatial positioning of these color centers.
Theoretical calculations led by Steven Louie, a faculty senior scientist at Berkeley Lab and distinguished professor of physics at UC Berkeley, provided candidates for the UV color center atomic configuration to help explain why their brightness depended on the twist angle. The light emission process involves an excited electron wandering around and recombining with a hole at the color center. But a typical hBN structure has many traps that could capture the electrons, preventing light emission. “Twisting the crystal layers removes many of these traps, or ‘quantum parking lots,’ near the interface,” said Louie.
The team next intends to prepare samples that allow atomic characterization to pinpoint the specific atomic structures behind this mechanism and add additional levels of control. “The work is pointing us in the direction of new types of mechanisms that we can use to control the emission even better, and this is very important for many applications in quantum information sciences,” said Aloni.
Science paper:
Nature Materials
See the full article here .
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In the world of science, The Lawrence Berkeley National Laboratory (Berkeley Lab) is synonymous with “excellence.” Thirteen Nobel prizes are associated with Berkeley Lab. Seventy Lab scientists are members of the The National Academy of Sciences, one of the highest honors for a scientist in the United States. Thirteen of our scientists have won the National Medal of Science, our nation’s highest award for lifetime achievement in fields of scientific research. Eighteen of our engineers have been elected to the The National Academy of Engineering, and three of our scientists have been elected into the Institute of Medicine. In addition, Berkeley Lab has trained thousands of university science and engineering students who are advancing technological innovations across the nation and around the world.
Berkeley Lab is a member of the national laboratory system supported by the U.S. Department of Energy through its Office of Science. It is managed by the University of California and is charged with conducting unclassified research across a wide range of scientific disciplines. Located on a 202-acre site in the hills above the University of California- Berkeley campus that offers spectacular views of the San Francisco Bay, Berkeley Lab employs approximately 3,232 scientists, engineers and support staff. The Lab’s total costs for FY 2014 were $785 million. A recent study estimates the Laboratory’s overall economic impact through direct, indirect and induced spending on the nine counties that make up the San Francisco Bay Area to be nearly $700 million annually. The Lab was also responsible for creating 5,600 jobs locally and 12,000 nationally. The overall economic impact on the national economy is estimated at $1.6 billion a year. Technologies developed at Berkeley Lab have generated billions of dollars in revenues, and thousands of jobs. Savings as a result of Berkeley Lab developments in lighting and windows, and other energy-efficient technologies, have also been in the billions of dollars.
Berkeley Lab was founded in 1931 by Ernest Orlando Lawrence, a University of California-Berkeley physicist who won the 1939 Nobel Prize in physics for his invention of the cyclotron, a circular particle accelerator that opened the door to high-energy physics. It was Lawrence’s belief that scientific research is best done through teams of individuals with different fields of expertise, working together. His teamwork concept is a Berkeley Lab legacy that continues today.
History
1931–1941
The laboratory was founded on August 26, 1931, by Ernest Lawrence, as the Radiation Laboratory of the University of California-Berkeley, associated with the Physics Department. It centered physics research around his new instrument, the cyclotron, a type of particle accelerator for which he was awarded the Nobel Prize in Physics in 1939.
LBNL 88 inch cyclotron.
Throughout the 1930s, Lawrence pushed to create larger and larger machines for physics research, courting private philanthropists for funding. He was the first to develop a large team to build big projects to make discoveries in basic research. Eventually these machines grew too large to be held on the university grounds, and in 1940 the lab moved to its current site atop the hill above campus. Part of the team put together during this period includes two other young scientists who went on to establish large laboratories; J. Robert Oppenheimer founded The DOE’s Los Alamos Laboratory, and Robert Wilson founded The DOE’s Fermi National Accelerator Laboratory.
1942–1950
Leslie Groves visited Lawrence’s Radiation Laboratory in late 1942 as he was organizing the Manhattan Project, meeting J. Robert Oppenheimer for the first time. Oppenheimer was tasked with organizing the nuclear bomb development effort and founded today’s Los Alamos National Laboratory to help keep the work secret. At the RadLab, Lawrence and his colleagues developed the technique of electromagnetic enrichment of uranium using their experience with cyclotrons. The “calutrons” (named after the University) became the basic unit of the massive Y-12 facility in Oak Ridge, Tennessee. Lawrence’s lab helped contribute to what have been judged to be the three most valuable technology developments of the war (the atomic bomb, proximity fuse, and radar). The cyclotron, whose construction was stalled during the war, was finished in November 1946. The Manhattan Project shut down two months later.
1951–2018
After the war, the Radiation Laboratory became one of the first laboratories to be incorporated into the Atomic Energy Commission (AEC) (now The Department of Energy . The most highly classified work remained at Los Alamos, but the RadLab remained involved. Edward Teller suggested setting up a second lab similar to Los Alamos to compete with their designs. This led to the creation of an offshoot of the RadLab (now The DOE’s Lawrence Livermore National Laboratory) in 1952. Some of the RadLab’s work was transferred to the new lab, but some classified research continued at Berkeley Lab until the 1970s, when it became a laboratory dedicated only to unclassified scientific research.
Shortly after the death of Lawrence in August 1958, the UC Radiation Laboratory (both branches) was renamed the Lawrence Radiation Laboratory. The Berkeley location became the Lawrence Berkeley Laboratory in 1971, although many continued to call it the RadLab. Gradually, another shortened form came into common usage, LBNL. Its formal name was amended to Ernest Orlando Lawrence Berkeley National Laboratory in 1995, when “National” was added to the names of all DOE labs. “Ernest Orlando” was later dropped to shorten the name. Today, the lab is commonly referred to as “Berkeley Lab”.
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From the 1950s through the present, Berkeley Lab has maintained its status as a major international center for physics research, and has also diversified its research program into almost every realm of scientific investigation. Its mission is to solve the most pressing and profound scientific problems facing humanity, conduct basic research for a secure energy future, understand living systems to improve the environment, health, and energy supply, understand matter and energy in the universe, build and safely operate leading scientific facilities for the nation, and train the next generation of scientists and engineers.
The Laboratory’s 20 scientific divisions are organized within six areas of research: Computing Sciences; Physical Sciences; Earth and Environmental Sciences; Biosciences; Energy Sciences; and Energy Technologies. Berkeley Lab has six main science thrusts: advancing integrated fundamental energy science; integrative biological and environmental system science; advanced computing for science impact; discovering the fundamental properties of matter and energy; accelerators for the future; and developing energy technology innovations for a sustainable future. It was Lawrence’s belief that scientific research is best done through teams of individuals with different fields of expertise, working together. His teamwork concept is a Berkeley Lab tradition that continues today.
Berkeley Lab operates five major National User Facilities for the DOE Office of Science:
The Advanced Light Source (ALS) is a synchrotron light source with 41 beam lines providing ultraviolet, soft x-ray, and hard x-ray light to scientific experiments.
The DOE’s Lawrence Berkeley National Laboratory Advanced Light Source.
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Berkeley Lab Laser Accelerator (BELLA) Center
The DOE Joint Genome Institute supports genomic research in support of the DOE missions in alternative energy, global carbon cycling, and environmental management. The JGI’s partner laboratories are Berkeley Lab, DOE’s Lawrence Livermore National Laboratory, DOE’s Oak Ridge National Laboratory (ORNL), DOE’s Pacific Northwest National Laboratory (PNNL), and the HudsonAlpha Institute for Biotechnology . The JGI’s central role is the development of a diversity of large-scale experimental and computational capabilities to link sequence to biological insights relevant to energy and environmental research. Approximately 1,200 scientist-users take advantage of JGI’s capabilities for their research every year.
The LBNL Molecular Foundry is a multidisciplinary nanoscience research facility. Its seven research facilities focus on Imaging and Manipulation of Nanostructures; Nanofabrication; Theory of Nanostructured Materials; Inorganic Nanostructures; Biological Nanostructures; Organic and Macromolecular Synthesis; and Electron Microscopy. Approximately 700 scientist-users make use of these facilities in their research every year.
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DOE’s NERSC National Energy Research Scientific Computing Center at Lawrence Berkeley National Laboratory.
NERSC Hopper Cray XE6 supercomputer.
NERSC Cray XC30 Edison supercomputer.
The Genepool system is a cluster dedicated to the DOE Joint Genome Institute’s computing needs. Denovo is a smaller test system for Genepool that is primarily used by NERSC staff to test new system configurations and software.
NERSC PDSF computer cluster in 2003.
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Cray Shasta Perlmutter SC18 AMD Epyc Nvidia pre-exascale supercomputer.
NERSC is a DOE Office of Science User Facility.
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Berkeley Lab has a major role in two DOE Energy Innovation Hubs. The mission of the Joint Center for Artificial Photosynthesis (JCAP) is to find a cost-effective method to produce fuels using only sunlight, water, and carbon dioxide. The lead institution for JCAP is the California Institute of Technology and Berkeley Lab is the second institutional center. The mission of the Joint Center for Energy Storage Research (JCESR) is to create next-generation battery technologies that will transform transportation and the electricity grid. DOE’s Argonne National Laboratory leads JCESR and Berkeley Lab is a major partner.
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