What are you aiming for?

I am engaged in research that is working towards the objective of being able to write information onto a single electron, and then communicate that information using light. The key to realizing this will be nanotechnology.

Specifically, I am researching nanostructures in semiconductors, referred to as “quantum dots” (where 1 nanometer is equivalent to 1 billionth of a meter, and one quantum dot comprises roughly several hundred atoms or molecules). One semiconductor quantum dot can enclose just one conductive “electron”. These electrons are different from inner shell electrons and valence electrons, which exist as a result of atoms and their bonding. They can enter and exit quantum dots easily, and can also change their form into “light”. In other words, using quantum dots opens a path which allows us to handle individual electrons, or individual photons, if they change their form, as if with a pair of tweezers.

Up until now, we needed multiple electrons in order to create and communicate a single piece of information. If, however, the unit of information becomes a single electron, we become able to handle information using significantly smaller quantities of energy (electricity). Furthermore, the light emitting from these semiconductor quantum dot electrons has some superior properties not seen until now. For example, it is possible to accurately control the color (wavelength) of the light. Since the wavelength of this light is not impacted by the temperature of its environment, it is possible to build light sources and elements for use in optical communications that do not waste excess energy through processes such as cooling.

Information is a major force that supports our lives, our society and our industry. A wide range of information is transmitted across computers and over the internet, through TV, financial institutions and medical treatment centers, and we make decisions about things based on this information. The substance of this information in the real world is the electrons that run around within electronic circuits, while optical communications are used to transmit information to places far away. Developments in “information electronics”, where information is generated using electrons, and converted into light before being transmitted, now allows massive quantities of images and numerical data to be processed in a single instant, and communicated immediately around the world.

Fig. 1 Pattern diagram of semiconductor quantum dot. A single electron can be enclosed and stored, and turned efficiently into light.

 

What sort of equipment are you using to perform what type of experiments?

When working with semiconductor quantum dots, it is vital that there is not a single atom of impurity such as nitrogen or oxygen from the air present. For that reason, we create an extreme vacuum, similar to being in space, in the laboratory, and within that, manufacture semiconductor quantum dots using a device known as the molecular beam epitaxy, which builds up atoms and molecules one by one (Fig. 2). Next, we research the state of the electrons within the manufactured quantum dots in detail. To do this, we need light, of course. We convert the state of each electron, one by one, into light information, and read it. The measuring device used to do this is rather large, and many graduate students cooperated in its building (Fig. 3).

Fig. 2: Using a molecular beam epitaxy device to create extremely pure semiconductor quantum dots within a super-high vacuum. The students engage in this job with great passion.	Fig. 3: An experiment in which light is used to measure the state of the electrons inside the quantum dot. We use a large, special laser light source, high-performance optical detector and superconductor magnet, etc.
	Fig. 4: Electron microscope photograph of a semiconductor quantum dot actually being manufactured. Observing a cross-section of the sample, the yellow wavy line area is a quantum dot, configured from different atoms to the area around it. Each small bright spot is an atom.

 

In terms of experimentation, we are currently engaged in attempts to the create semiconductor quantum dots with a controlled size and shape, and in a specified position (Fig. 4). The state of the electrons within these quantum dots is measured using light. At the same time, this is also basic research into the conversion of information created by electrons into light information. Furthermore, the electrodes and optical fibers used to insert and remove electrons and light are connected to nanostructures. In the near future, I hope we will be able to actually produce laser elements using a new methodology.

 

What are you aiming for next?

Quantum dots are incredibly tiny – they comprise only a few hundred atoms and molecules. The ability to dictate the size and shape of these dots, and create them in a specified position, is an extreme objective (dream?) to have, considering their atomic/molecular scale. We will need to come up with completely new manufacturing methods, never before seen in the world of semiconductor engineering, in order to do this. My focus is on bioengineering and using the structures of natural organisms. I have already begun looking into this, and have had some success in my research.