Scientists at Argonne Identify and Design Atomic Quantum Emitters for Upcoming Instruments
Quantum Emitters
By successfully designing and precisely positioning single-photon sources at the atomic scale within ultrathin 2D materials, researchers at the U.S. Department of Energy’s (DOE) Argonne National Laboratory, in partnership with the University of Illinois Urbana-Champaign, have made significant strides in quantum technology. This ground-breaking discovery paves the way for future quantum advancements by utilizing the Centre for Nanoscale Materials’ (CNM) cutting-edge Quantum Emitter Electron Nanomaterial Microscope (QuEEN-M).
Often referred to as tiny switches, quantum emitters act as the “bits” of many quantum technologies by accurately activating the flow of individual light particles called photons. These crucial elements are produced by atomic-scale flaws in materials, and the future of quantum computing, secure communication, and ultraprecise sensing depends on their capacity to produce light with great precision. But historically, finding and managing these atomic light switches has proven to be a significant scientific difficulty.
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The scientists identified and even produced these vital light sources in the ultrathin material hexagonal boron nitride with the specialized QuEEN-M at the CNM, a DOE Office of Science user facility. The researchers have paved the way for the creation of materials with unique quantum characteristics for upcoming devices by linking the atomic structure of the quantum emitters to their optical behavior.
“The challenge in studying quantum emitters is that their optical behavior is determined by their atomic structure, which is very hard to observe directly,” noted Jianguo Wen, an Argonne materials scientist and Interim Group Leader for Electron and X-ray Microscopy. Traditional research had to choose between using thicker samples for light emission observation and thinner samples for atomic structure analysis.
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Wen and his group used the high-resolution QuEEN-M microscope in combination with cathodoluminescence spectroscopy to get around this. By directing an electron beam onto the substance, this method produces light. Important details regarding the makeup of the quantum emitter and the locations of its defect sites can be inferred from the color and intensity of the light that is released. Using contemporary electron optics and detectors, the QuEEN-M is a uniquely constructed electron microscope.
Equipped with a Cathodoluminescence (CL) spectrometer, an ultrafast pulser, and a beam blanker, the QuEEN-M is a Thermo Fisher Spectra 300 probe-corrected scanning transmission electron microscope. EDS/EELS mapping, CL spectroscopy, 4D-STEM, and real-space atomic-resolution imaging are all made possible by this potent device, which also offers great spatiotemporal resolution.
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A crucial finding was that the light signal from the quantum emitters is greatly strengthened, increasing by up to 120 times, when layers of hexagonal boron nitride are twisted at particular angles to form “twisted interfaces.” With an accuracy of fewer than 10 nanometers, the researchers were able to locate the emitters with remarkable precision with this boosted signal. By employing this extremely precise technique, the group was able to determine that a blue quantum emitter in hexagonal boron nitride was actually a carbon dimer, which is a pair of vertically stacked carbon atoms.
Surprisingly, by incorporating carbon into the material and activating emitters at certain locations with the electron beam, the researchers were able to produce these quantum emitters on demand. The significance of this control was emphasized by Thomas Gauge, a physicist at Argonne: “The ability to link the atomic structure with the light it emits allowed for the precise engineering of these quantum emitters, which we can now create and modify on demand using an electron beam.” “The ability to place these photons with high accuracy is crucial for the quantum electronics of the future,” said Benjamin Diroll, another Argonne scientist.
Scientists may create materials with unique quantum properties that can be precisely positioned on a chip with these precise engineering capabilities. Future quantum technologies are anticipated to be developed more quickly, with the potential to integrate these tailored materials with other technologies to improve signals and transmit information more effectively.
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The CNM’s Electron and X-ray Microscopy (EXM) group has a larger mandate that includes quantum emitter research. From the atomic scale to the device level, the EXM group seeks to characterize and eventually regulate the functions of materials. The CNM’s five scientific themes—Quantum coherence by design, interfaces, assembly, and fabrication for emergent features, ultrafast dynamics and non-equilibrium processes, AI/ML Accelerated analytics and automation, and nanoscale discovery for new energy technologies—all fit with this mission.
The EXM team provides great spatial, energy, and temporal resolution, enabling previously unheard-of comprehension of material properties at the nano to atomic scale. For instance, single atoms buried within structures can now be resolved using electron microscopes. With important tools like Ultrafast Electron Microscopy (UEM), the EXM group focusses on nanoscale dynamics.
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The UEM is made to use electrons to study ultrafast (sub-picosecond) structural and chemical dynamics in materials at the nanoscale. To comprehend transitory events in materials, the UEM provides sub-nanometer, sub-picosecond, and sub-electronvolt spatial, temporal, and energy resolutions. It is currently available to users. The approximate temporal resolution, spatial resolution, and energy resolution are 1 ps, 1 nm, and 1 eV, respectively, according to its technical specifications. This instrument, which is based on Altos Photonics lasers and a JEOL JEM2100PLUS electron microscope, offers information about short-lived metastable phases and rapid dynamics in materials that are not achievable with conventional electron microscopes.
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The Hard X-ray Nanoprobe (HXN) in APS Sector 26 is one of the strong X-ray microscopy tools used by the EXM group. A hard X-ray beam that is adjustable over the 6–12 keV spectral range and focused down to 25 nm onto the material is delivered by the HXN facility, a joint CNM/APS venture at APS beamline 26-ID. For mapping most elements and investigating crystalline thin films, devices, interfaces, and inner-shell electronic resonances, this energy range works best.
Scanning nanodiffraction, Bragg ptychography (5 nm resolution), and multimodal chemical and structural nanoimaging (around 30 nm resolution) are all supported by the HXN. The two components of the X-ray microscopy effort are the development of time-resolved pump-probe Bragg diffraction microscopy capabilities at the HXN for operando picosecond/nanoscale studies and the extension of Bragg ptychographic imaging into the dynamical diffraction regime using AI/ML-enabled techniques for complete 3D visualization of deep defects.
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The DOE Office of Basic Energy Sciences, the Laboratory Directed Research and Development program at Argonne, and QIS research funds all contributed to this quantum emitter study, which was published in Advanced Materials. The National Nanotechnology Initiative’s main infrastructure investment comprises five DOE Nanoscale Science Research Centers (NSRCs), including the CNM.
This ability to engineer quantum features atom by atom and alter matter at the most fundamental level is like switching from big, unreliable old switches to installing flawless, atomic-scale microprocessors that run with perfect precision.
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