The Applied Physics research group at the Vrije Universiteit Brussel has developed a new generation of optical computers, known as coherent Ising machines. These machines can be considerably faster and more energy-efficient than the current conventional digital computer when it comes to solving optimisation problems. Until now, they have been very large, expensive and difficult to build, because they use miles of optical fibres and powerful laser systems. A team led by Fabian Böhm, Professor Guy Verschaffelt and Professor Guy Van der Sande has greatly reduced and simplified these machines into a portable system. In the future, the system can be shrunk to just a few millimetres in size. For the first time, these machines will be cheap and practical enough for commercial use. The research results have been published in the journal Nature Communications.
Optimisation algorithms are everywhere: they calculate the most efficient transport plan for railways, the best timing for smart traffic lights or the fastest route to our destination via our smartphone. But they require a great deal of computing power, which traditional computers have great difficulty with. This is why several research institutes and large companies such as Google, IBM, HP and NTT are looking for alternatives to the conventional digital computer to solve these kinds of problems more quickly. Today, the most promising contenders as an alternative are quantum computers and coherent Ising machines. Unlike digital computers, they don’t try every possibility to find the optimal solution; instead they evolve to gravitate towards the most likely solution, similar to the way in which water always flows to the lowest point in a valley. The main difference between the two contenders is that optical computers operate on classic laser light, where quantum computers make use of the sometimes strange properties of quantum physics.
A hundred times faster
Research groups in Japan and the US have shown that coherent Ising machines can be at least 100 times faster than digital computers. They present comparable and even better performance than quantum computers while being cheaper. “However, in their current form, these machines are still too far removed from commercial applications,” researcher Fabian Böhm explains. “Because they use miles of optical fibres and high-powered laser systems, they are simply too complex, too expensive and too large. The new design developed by our team at VUB makes them small and cheap enough to replace digital computers.”
From ready-made components
Currently, a complete lab is needed to house a single coherent Ising machine. The approach of the VUB researchers is changing this, with an extremely inexpensive and compact set-up based on standard optical and electronic components that are also used in the internet. As a result, the optical computer can be composed entirely of ready-to-use commercial components and can be easily reconstructed anywhere. Moreover, these components can take the form of photonic chips in the future, which will drastically reduce their size and cost.