This is a bowtie-shaped nanoparticle made of silver with a trapped semiconductor quantum dot (indicated by the red arrow). Credit: Weizmann Institute of Science
Bowtie-shaped Nanostructures may advance development of Quantum devices. Made of silver, these may help bring the dream of quantum computing and quantum information processing closer to reality. They greatly simplify the experimental conditions for studying quantum phenomena and may one day be developed into crucial components.
Led by Prof. Gilad Haran of Weizmann’s Chemical Physics Department the team manufactured 2D bowtie-shaped silver nanoparticles with a minuscule gap of about 20 nanometers in the center. The researchers then dipped the “bowties” in a solution containing quantum dots, tiny semiconductor particles that can absorb and emit light, each 6-8nm across. In the course of the dipping, some quantum dots became trapped in the bowtie gaps.
Under exposure to light, the trapped dots became “coupled” with the bowties ie formation of a mixed state, in which a photon in the bowtie is shared with the quantum dot. The coupling was sufficiently strong to be observed even when the gaps contained a single quantum dot, as opposed to several. The bowtie nanoparticles could thus be prompted to switch from one state to another: from a state without coupling to quantum dots, before exposure to light, to the mixed state characterized by strong coupling, following such exposure.
The ability to control the coupling of quantum dots may one day be employed in the manufacture of switches for computing or encryption devices relying on quantum phenomena. Most importantly, these can function at room temperature.
The Weizmann scientists managed to design their bowtie system thanks to advances in nanotechnology – including electron beam lithography, used to fabricate the bowties and to facilitate the introduction of quantum dots into their gaps – and the advent of computational programs providing data analysis. They also relied on the recently improved understanding of electron oscillations triggered by light in metals, which constitute the physical source of the coupling between the bowtie nanoparticles and the quantum dots: Such oscillations are known to be strongest on the metal surface. In the new bowtie-shaped particles, the electromagnetic field generated by these oscillations is extremely concentrated as it is focused to the narrow portion of the bowtie.
The high concentration ensures tight control over the coupling, and this control, in turn, is essential for potential future quantum applications. None of the systems built in the past to study quantum interactions between light and matter operated on such a small scale or were able to reduce experiments to the level of individual quantum dots, as was done in the Weizmann study.
http://wis-wander.weizmann.ac.il/chemistry/building-better-bowtie
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