Spin Wave Computing: New Waveguide for Logic Gates Enhances Performance of Analog Computer

Compared to digital computers, analog computers are less precise since they represent data using physical quantities and perform operations using continuous functions. To enable analog computers to process large amounts of data, experts use light waves produced by lasers or incoherent sources.

Challenges in Light-Based Computing

Light-based computing uses photons to perform digital computations. The light produced by the sources is used as a primary means to carry out data communications, data processing, numerical calculations, and reasoning.

Optics are a natural choice for wave-based computing since light waves can be manipulated smoothly and read off easily once a computation is done. Optical wavelengths of light are also considered when harnessing the potential of analog computers for new types of super-efficient AI and avoiding analog-to-digital conversions.

However, optical computing also has some limitations. Aside from the difficulty in developing photonic crystals, computation also becomes a complex process because of the interaction of various signals. Optical analog computers can be bulky and oversized enough for commercial uses. The optical components are also vulnerable to imperfections, leading to computation errors.

Resurgence of Analog Computers

In a recent breakthrough, however, a team of experts has taken an essential step towards the next generation of analog computers. Scientists from Japan and Switzerland, led by Kanta Mori, did collaborative research where they created new types of logic gates based on spin waves.

Spin waves refer to the waves generated when all the electrons in a system shift the alignment of their spins in one direction and simultaneously. With wavelengths of around 100 nanometers, they provide a different vision for analog computing, which is more aligned with their digital counterparts.

To manipulate the spin waves, the researchers rely on "magnonics", an emerging research field which combines the study of waves and magnetism. Mori and his colleagues used this to develop a new waveguide that can provide the basis for the logic gates of spin-wave computers. The result of their study is described in the paper "Orientation-dependent two-dimensional magnonic crystal modes in an ultralow-damping ferrimagnetic waveguide containing repositioned hexagonal lattices of Cu disks."

Study co-author Taichi Goto noted that in terms of practicality and terms of research, there is a higher potential to make analog computing more affordable by using spin-wave technology. While cooling is required in some magnetic materials, the device developed by the researchers can operate at room temperature. This makes spin-wave technology more affordable since there is no need for cooling facilities or running costs like those for quantum computers that use superconductors.

The spin-wave waveguide developed by the team has the potential to provide the foundation for analog logic gates and other important components of any analog computer. Such magnonic waveguides are typically produced by processing yttrium-iron-garnet (YIG) into rod-like materials. By adding two-dimensional copper with a hexagonal lattice to a YIG substrate, the internal reflectivity of the waveguide is increased, reducing losses within the waveguide.

An antenna is constructed directly on the insulating substrate to generate spin waves in the device. As a result, the hexagonally latticed two-dimensional copper can reflect and channel the same spin waves.

The size and structure of the antenna allow the wavelength of spin waves to be altered, making it easier to control some properties such as localization, diffraction, refraction, and wave phase interference. This basic property enables the creation of unique functionalities that are challenging to replicate elsewhere.