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Squeezing Quantum Dots to Tune Their Wavelength, Allow Interaction

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WASHINGTON, D.C., July 11, 2019 — A technique for squeezing quantum dots, developed at the U.S. Naval Research Laboratory (NRL), could enable many quantum dots to interact with each other in a quantum network. The new technique provides a way to realize quantum dots that are tuned precisely in both their wavelength and position.

The size of a quantum dot determines its emission wavelength, but no two quantum dots have exactly the same size and shape when they are created. To enable quantum dots to emit single photons with the same wavelength, and positioned less than 1 millionth of a meter apart, the researchers patterned strain using local phase transitions to selectively tune individual quantum dots that were embedded in a photonic architecture. The patterning was implemented using in-operando laser crystallization of a thin HfO2 film “sheath” on the surface of a GaAs waveguide.

Schematic of a nanoscale structure called a 'photonic crystal waveguide' that contains quantum dots that can interact with one another when they are tuned to the same wavelength. Courtesy of Chul Soo Kim, U.S. Naval Research Laboratory.
Schematic of a nanoscale structure called a photonic crystal waveguide that contains quantum dots that can interact with one another when they are tuned to the same wavelength. Courtesy of Chul Soo Kim, U.S. Naval Research Laboratory.

“Instead of making quantum dots perfectly identical to begin with, we change their wavelength afterward by shrink-wrapping them with laser-crystallized hafnium oxide,” researcher Joel Grim said. “The shrink wrap squeezes the quantum dots, which shifts their wavelength in a very controllable way.”

Using this approach, the researchers tuned multiple quantum dots into resonance within the same waveguide and demonstrated a quantum interaction through superradiant emission from three quantum dots. The team believes that precision in both wavelength and position is possible not just for two or three, but for many quantum dots in an integrated circuit, using the new technique.

“NRL’s new method for tuning the wavelength of quantum dots could enable new technologies that use the strange properties of quantum physics for computing, communication, and sensing,” researcher Allan Bracker said. “It may also lead to neuromorphic, or brain-inspired, computing based on a network of tiny lasers.”

The research was published in Nature Materials (https://doi.org/10.1038/s41563-019-0418-0). 

Photonics.com
Jul 2019
GLOSSARY
quantum dots
Also known as QDs. Nanocrystals of semiconductor materials that fluoresce when excited by external light sources, primarily in narrow visible and near-infrared regions; they are commonly used as alternatives to organic dyes.
quantum optics
The area of optics in which quantum theory is used to describe light in discrete units or "quanta" of energy known as photons. First observed by Albert Einstein's photoelectric effect, this particle description of light is the foundation for describing the transfer of energy (i.e. absorption and emission) in light matter interaction.
nanophotonics
The study of how light interacts with nanoscale objects and the technology of applying photons to the manipulation or sensing of nanoscale structures.
Research & TechnologyAmericasNaval Research Laboratorypositioningquantum dotsquantum opticsquantum communicationsnanonanophotonicsdefenseCommunications

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