KAIST Develops Quantum Dot Light Source Purity Enhancement Technology... Removes Only Background Noise Signals

Schematic example of applying the quenching technique using a focused ion beam to quantum dots formed on the apex structure of a hexagonal pyramid

[Asia Economy Reporter Seolgina Jo] The research team led by Professor Yong-Hoon Cho of the Department of Physics at the Korea Advanced Institute of Science and Technology (KAIST) announced on the 29th that they have succeeded in developing a technology to enhance the single-photon purity of a single quantum dot formed at the apex of a semiconductor pyramid structure using a focused ion beam.

The technology developed through this research is expected to be utilized not only for quantum light sources precisely controlled in position, such as those at pyramid apexes, but also for various quantum photonic devices including high-density quantum dot-based quantum light sources and electrically driven quantum dot-based quantum light sources.

A quantum light source emits photons one at a time without emitting two or more photons simultaneously. Due to the no-cloning theorem of quantum mechanics, which states that single quantum information cannot be copied, it can be used for quantum communication that is secure against hacking. In particular, semiconductor-based quantum dots are widely studied as practical quantum light sources because they can be integrated on a chip and electrically driven.

However, semiconductor quantum dot-based quantum light sources coexist with background noise signals generated from the surrounding structures of the quantum dots. This background noise weakens the quantum properties of the light, increasing the possibility of quantum light being hacked. Therefore, to use semiconductor quantum dots as practical quantum light sources, it is important to reduce background noise and significantly improve the signal-to-noise ratio of the quantum light.

Previous studies have attempted to reduce background noise around quantum light sources and improve the signal-to-noise ratio by etching away parts that emit background noise signals or by blocking them with metal. However, these methods had the drawback of either reducing the quantum light signal from the quantum dots or damaging the structures around the quantum dots.

Result of selectively irradiating the convergent ion beam on the areas of a hexagonal pyramid structure excluding the vertices to quench them

Professor Yong-Hoon Cho’s research team developed a technology that effectively removes only the background noise signals without physically damaging the structures around the quantum dots or weakening the quantum light signals, using a focused ion beam, and applied it to quantum dots precisely formed at the apex of semiconductor pyramid structures.

The focused ion beam technology has been widely used in fields such as semiconductor technology and biology for fabricating nanostructures through etching or preparing samples for imaging tests. Professor Cho’s team noted that by precisely controlling the type and conditions of the focused ion beam, it is possible to selectively quench only the background noise signals at nanoscale spatial resolution without damaging the semiconductor structures.

Using this method, they succeeded in nanoscale quenching of background noise signals around quantum dots located at the apex of semiconductor pyramid structures, significantly improving the single-photon purity, an indicator of how close the emitted luminescence signal is to ideal quantum light. This result is meaningful as it can be used not only for quantum dots with controlled positions such as pyramid apexes but also for selectively removing unwanted signals in various semiconductor quantum dot-based quantum photonic devices and photonic integrated circuits, thereby enhancing device performance.

Professor Yong-Hoon Cho, who led the research, said, "We have developed a high-resolution technique using a focused ion beam to selectively quench unwanted surrounding background noise signals, which will serve as a foundational technology applicable to various quantum photonic devices, photonic integrated circuits, and display fields."

The research, co-first authored by Minho Choi and Seongmoon Jeon, doctoral candidates in the Department of Physics at KAIST, was published in the July 27 issue of `ACS Nano,' a leading international journal in the field of nanoscience.

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