Development of quantum tech is anchored on traceable standards

The team's methodology not only corrects image distortions but also enhances the accuracy and reliability of quantum dot device fabrication.

Devices leveraging quantum dots to capture light, such as chip-scale lasers and optical amplifiers, have successfully transitioned from laboratory prototypes to commercial markets. However, the journey has been slower for newer quantum dot-based devices due to the intricate precision required in aligning individual dots and the optics guiding the emitted radiation.

One significant challenge arises from errors in the process of localizing quantum emitters using microscopy to guide the lithographic placement of photonic structures. These errors, stemming from both microscopy and lithography measurements, hinder registration accuracy, thereby limiting device performance and production yield.

To tackle this obstacle, researchers at the National Institute of Standards and Technology (NIST) and the University of Maryland have devised standards and calibrations for optical microscopes employed in precisely centering quantum dots within photonic chips.

Their method achieves a remarkable precision down to 10-20 nm across the entire image from an optical microscope, facilitating the correction of numerous individual quantum dots. According to their model, calibrating microscopes with these new standards could potentially increase the number of high-performance devices by up to a hundred-fold. Importantly, the standards and calibrations developed by the collaborators adhere to the International System of Units (SI).

“The seemingly straightforward task of locating a quantum dot and positioning a photonic component on it poses a challenging measurement problem,” remarked NIST researcher Craig Copeland.

During the typical measurement process, errors accumulate as researchers use an optical microscope to pinpoint quantum dots randomly dispersed on a semiconductor material’s surface. Ignoring the shrinkage of semiconductor materials at ultracold temperatures exacerbates these errors. Moreover, inaccuracies in the fabrication process used for calibration standards compound these measurement errors, further affecting photonic component placement.

To address these challenges, the NIST team devised two types of traceable standards for calibrating optical microscopes. Firstly, at room temperature, they utilized an array of nanoscale holes in a metal film, ensuring precise measurements of hole positions traceable to the SI. Then, at cryogenic temperatures, they calibrated ultracold optical microscopes by constructing an array of pillars on a silicon wafer, leveraging the known shrinkage properties of silicon at low temperatures.

The team’s methodology not only corrects image distortions but also enhances the accuracy and reliability of quantum dot device fabrication. Beyond quantum dot devices, these traceable standards and calibrations hold promise for improving accuracy in other demanding applications of optical microscopy, such as imaging brain cells and mapping neural connections.

Additionally, they offer potential benefits in nanoparticle characterization, microsystem tracking, and semiconductor metrology.

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