Posted By: baltazar
April 3, 2024
Accurate alignment of quantum dots with photonic components is critical for extracting the radiation emitted by the dots. In this illustration, a quantum dot centered in the optical “hotspot” of a circular grating (center dot in the inset) emits more light than a dot that is misaligned (off-center dot in the inset). Credit: S. Kelley/NIST
Traceable microscopy could improve the reliability of quantum information technologies, biological imaging, and more.
Devices that capture the brilliant light from millions of quantum dots, including chip-scale lasers and optical amplifiers, have made the transition from laboratory experiments to commercial products. But newer types of quantum-dot devices have been slower to come to market because they require extraordinarily accurate alignment between individual dots and the miniature optics that extract and guide the emitted radiation.
Breakthrough in Quantum Dot Alignment
Researchers at the National Institute of Standards and Technology (NIST) and their colleagues have now developed standards and calibrations for optical microscopes that allow quantum dots to be aligned with the center of a photonic component to within an error of 10 to 20 nanometers (about one-thousandth the thickness of a sheet of paper). Such alignment is critical for chip-scale devices that employ the radiation emitted by quantum dots to store and transmit quantum information.
Enhancing Quantum Device Performance
For the first time, the NIST researchers achieved this level of accuracy
How close the measured value conforms to the correct value.
” data-gt-translate-attributes=”[{"attribute":"data-cmtooltip", "format":"html"}]” tabindex=”0″ role=”link”>accuracy across the entire image from an optical microscope, enabling them to correct the positions of many individual quantum dots. A model developed by the researchers predicts that if microscopes are calibrated using the new standards, then the number of high-performance devices could increase by as much as a hundred-fold.
That new ability could enable quantum information technologies that are slowly emerging from research laboratories to be more reliably studied and efficiently developed into commercial products.
Calibration Challenges and Solutions
In developing their method, Craig Copeland, Samuel Stavis, and their collaborators, including colleagues from the Joint Quantum Institute (JQI), a research partnership between NIST and the University of Maryland, created standards and calibrations that were traceable to the International System of Units (SI) for optical microscopes used to guide the alignment of quantum dots.
“The seemingly simple idea of finding a quantum dot and placing a photonic component on it turns out to be a tricky measurement problem,” Copeland said.
Addressing Microscopic Measurement Errors
In a typical measurement, errors begin to accumulate as researchers use an optical microscope to find the location of individual quantum dots, which reside at random locations on the surface of a semiconductor material. If researchers ignore the shrinkage of semiconductor materials at the ultracold temperatures at which quantum dots operate, the errors grow larger. Further complicating matters, these measurement errors are compounded by inaccuracies in the fabrication process that researchers use to make their calibration standards, which also affects the placement of the photonic components.
NIST’s Methodological Innovations
The NIST method, which the researchers described in an article posted online in Optica Quantum on March 18, identifies and corrects such errors, which were previously overlooked.
Illustration showing how traceable calibration of an optical microscope can correct for instrument imperfections that would otherwise result in misalignment of quantum dots with photonic components. Credit: S. Kelley/NIST
The NIST team created two types of traceable standards to calibrate optical microscopes—first at room temperature to analyze the fabrication process, and then at cryogenic temperatures to measure the location of quantum dots. Building on their previous work, the room-temperature standard consisted of an array of nanoscale