Waseda Institute for Advanced Study (WIAS)Waseda University

News

Challenges in Further Advancement of Quantum Beam Technology to light up the Micro-world Kazuyuki Sakaue, Assistant Professor (November, 2017)

  • Kazuyuki Sakaue,  Assistant Professor (November, 2017)

Quantum beam technology in everyday life

Have you heard of the term “quantum beam”? Although there may be some people who are not aware of beams, in our daily lives, we avail of numerous benefits from technology that uses quantum beams. My research concerns such quantum beams.

Substances in our surroundings are composed of atoms. An atom is further divided into an atomic nucleus and electrons around it. These electrons can be pulled apart from atoms or be added to them; this process is called ionization. Electromagnetic waves and particles with sufficient energy to ionize substances are called radiation. A quantum beam is artificially controlled radiation. Examples include X-rays and γ-rays.

I would like to introduce some concrete examples of how and in what scenarios such quantum beams are actually used.

Quantum beams are used in the medical field to treat tumors. Since quantum beams have high energy, they can destroy tumors. However, they also tend to destroy normal cells. To avoid destroying normal cells as much as possible, it is necessary to use a well-controlled quantum beam.

Semiconductor devices are components that form the foundation of various electronic devices. The lithography process for fabricating semiconductor devices employs quantum beams to execute the intricate processing required to engineer modern semiconductor components. The sophisticated patterns required on the semiconductors are made using a mask that is manufactured by a quantum beam. For finer processing, a finer mask is required. Quantum beams are used to create such masks.

Quantum beams are also useful for bioengineering new kinds of plants. An organism develops its body based on information in its DNA. By altering this DNA with quantum beams, it is possible to increase the probability of the occurrence of a plant with specific, desirable characteristics. In addition to preparing ornamental plants such as chrysanthemums of various colors, which had never existed previously, this technology has also been used to create plants that are better for both consumption and growth, such as rice with reduced glutelin and pears that are not easily prone to disease.

Increasing the accuracy of quantum beams to improve lives

The roles played by quantum beams are invisible at first glance. However, they support our lives in the background. One focus area in my research is to create a more accurate quantum beam. When using a quantum beam in the treatment of a tumor, the conventional method is to irradiate within a boundary reflecting the shape of the tumor, so that the beam strikes only the tumor and does not harm normal cells. However, when this method is used, it is necessary to create a dedicated boundary for each tumor. Therefore, a new method has been developed, in which even the smallest tumor can be targeted with great precision by a quantum beam. Even when making semiconductor devices, we can form a finer mask structure by controlling the quantum beam better, which makes it possible to engineer high-performance semiconductors.

Highly accurate light produced by quantum beams

In addition to using quantum beams directly, usable light can be created from a quantum beam. The most common method of extracting light from a quantum beam is by using a synchrotron accelerator. The electrons in the accelerator are energized, and an electron beam is generated by accelerating them. When this electron beam is bent, light is generated. When electrons wrapped with light energy are suddenly bent by a magnet, the coherent light is spun off and emitted in the form of very strong X-rays, which can be used in various fields.

Light sources that we usually encounter can be largely divided into two types: lamps and lasers. What is the difference between the two? It can be explained using the term “coherence.” Light exists in the form of waves; when these waves overlap, this light is called “coherent light.” The light of a lamp is incoherent and that of a laser is coherent (Figure 1). This is the major difference between a lamp and a laser. Lasers have good directivity, as their light is focused in a thin stream, making fine control possible. I aim to make a quantum beam that is highly coherent, like a laser.

eo74tdqv

Figure 1: The first wave image depicts light from a lamp, where light waves are random and incoherent. The bottom two are light from lasers, where the amplitude and phase of the waves align to produce coherent light. The black dots are electrons that emit light. The small bunch of electrons and precisely aligned bunches can produce coherent light as illustrated in the middle and bottom waves, respectively.

Toward the preparation of highly coherent light

What must we do to produce highly coherent quantum beams? When bending electrons and generating light from electrons, if electrons are regularly arranged, coherent light is emitted, as shown in Fig. 1. Let us suppose that each electron is a person that walks randomly on the street, as he/she wants. My job is to direct them and arrange them regularly in one direction; in other words, to make them march.

There are several problems with this. If some people walk at different speeds, the line collapses immediately. Electrons are negatively charged. As a result, proximate electrons repel each other by repulsive forces. If two people get too close, they try to distance themselves from each other, disrupting the marching row. It is necessary to eliminate these problems.

So, how can we arrange electrons to move in a regular and uniform manner? The important thing is for them to be aligned when light is generated. In the previous example of marching people, there is a judging seat to ensure that the march is perfectly regular. The electrons only need to be aligned properly when passing by this point. There are multiple methods to align them. One is to arrange the lines when starting a march, that is, to align the electrons properly as they are being generated. The other is to arrange them when they reach the judging seat, that is, to align the electrons properly after they are accelerated. I am using the latter. According to the theory of relativity, accelerated electrons become heavier. Because electrons do not repel as easily as they become heavier, they are easier to control, so I have adopted the method of aligning after acceleration.

Future prospects

Highly coherent lasers have the advantage of high intensity. X-ray lasers have already been developed and are used for structural analysis of proteins that do not require crystallization. Currently, I am conducting research on terahertz lasers. The terahertz laser is a laser with a light wavelength of 300 μm. Since it passes through paper and not through metal, it can be used for non-destructive inspection of envelopes of postal items.

To develop a laser with a shorter wavelength, more stringent control of electrons becomes necessary. However, as a goal, we can seek lasers of infinitely short wavelengths. We also plan to work on the development of new types of light by aligning electrons and on creating spiral light by devising measures to extract light.

     

Photo: Accelerator system in the laboratory of the Kikui-cho campus. The device visible at the back of the photograph on the left is the device used to control the electrons. This device was developed by us.

Interview and Composition: Seiko Aoyama/Chisato Hata/Tomohiro Homma
In cooperation with: Waseda University Graduate School of Political Science J-School

Page Top
WASEDA University

Sorry!
The Waseda University official website
<<https://www.waseda.jp/inst/wias/en/>> doesn't support your system.

Please update to the newest version of your browser and try again.

Continue

Suporrted Browser

Close