Research Bits: April 8

Annealing processor; microwave signal generation; phase change memory.


Annealing processor

Researchers from the Tokyo University of Science designed a scalable, fully-coupled annealing processor with 4096 spins on a single board with 36 CMOS chips, with parallelized capabilities for accelerated solving of combinatorial optimization problems.

“We want to achieve advanced information processing directly at the edge, rather than in the cloud, or performing preprocessing at the edge for the cloud,” said Takayuki Kawahara, a professor at Tokyo University of Science, in a statement. “We have realized a fully coupled LSI (Large Scale Integration) on one chip using 28nm CMOS technology. Furthermore, we devised a scalable method with parallel-operating chips and demonstrated its feasibility using FPGAs (Field-Programmable Gate Arrays) in 2022.”

The processor incorporates a “spin thread method” that enables 8 parallel solution searches, coupled with a technique that reduces chip requirements by about half compared to conventional methods. It operates at 10MHz with a power consumption of 2.9W (1.3W for the core part). This was practically confirmed using a vertex cover problem with 4096 vertices.

The researchers said the processor outperformed simulating a fully coupled Ising system on a PC (i7, 3.6GHz) using annealing emulation by 2,306 times. Additionally, it surpassed the core CPU and arithmetic chip by 2,186 times. The team aims to further develop the technology to achieve 2 million spins by 2030. [1]

Microwave signal generation

Researchers from Columbia University built a photonic chip that is able to produce high-quality, ultra-low-noise microwave signals using only a single laser, which they claim results in the lowest microwave noise ever observed in an integrated photonics platform.

Optical frequency division is a method of converting a high-frequency signal to a lower frequency, and can be used to generate  microwaves in which the noise has been strongly suppressed. “Typically, such a system requires multiple lasers and a relatively large volume to contain all the components,” said Alexander Gaeta, professor of applied physics and materials science and professor of electrical engineering at Columbia Engineering, in a release. “We have realized a device that is able to perform optical frequency division entirely on a chip in an area as small as 1 mm2 using only a single laser. We demonstrate for the first time the process of optical frequency division without the need for electronics, greatly simplifying the device design.”

The on-chip, all-optical device generates a 16-GHz microwave signal using two microresonators made of silicon nitride that are photonically coupled together. A single-frequency laser pumps both microresonators. One is used to create an optical parametric oscillator, while the second is adjusted to generate an optical frequency comb with a microwave spacing. [2]

Phase change memory

Researchers from the Korea Advanced Institute of Science and Technology (KAIST) and Samsung Electronics propose an ultra-low power phase changeable filament memory for neuromorphic computing.

The team claims it combines the advantages of both DRAM and NAND flash memory, offering both high speed and non-volatile characteristics while consuming 15 times less power than a conventional phase change memory device fabricated with a current lithography tool. [3]


[1] Taichi Megumi, Akari Endo, and Takayuki Kawahara, Scalable Fully-Coupled Annealing Processing System Implementing 4096 Spins Using 22nm CMOS LSI. IEEE Access.

[2] Zhao, Y., Jang, J.K., Beals, G.J. et al. All-optical frequency division on-chip using a single laser. Nature 627, 546–552 (2024).

[3] Park, SO., Hong, S., Sung, SJ. et al. Phase-change memory via a phase-changeable self-confined nano-filament. Nature (2024).

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