There exists a class of important computational problems that conventional computers are unable to address with reasonable efficiency. Such Combinatorial Optimization (CO) problems are pervasive in a wide range of critically important sectors of society, e.g. in business operations, manufacturing, and research, including man-power scheduling, vehicle routing, IC circuit layout, protein folding and DNA sequencing, efficient big-data clustering, election modelling, network diagnosis, modelling molecular dynamics, discovery of new medicines/chemicals/materials, and so forth. At present, the CO market size is of the order of €1B and is expected to exhibit a 56% market growth rate with a 2030 market size forecast at €50B.
Since conventional computers are ineffective in handling large CO problems, dedicated hardware – both quantum and quantum-inspired – are intensely researched and developed world-wide. While quantum computers currently receive most of the attention, they all face essentially insurmountable challenges in the near-term perspective. Quantum-inspired alternative – so-called Ising Machines – have been developed over the last 20 years by D-wave in superconducting technology and is commercially available. Various other types of Ising machines have been proposed, exploiting novel physical building blocks such as spintronic devices, memristor crossbars, metal-insulator relaxation oscillators, and degenerate optical parametric oscillators, as well as conventional CMOS technology with analog electric oscillators, and field programmable gate arrays (FPGAs). In particular, optical Coherent Ising Machines (CIM) have attracted great attention due to their high computational speed, a time-multiplexing method that provides all-to-all Ising spin connections, and the largest amount of supported Ising spins amongst all implementations. Nevertheless, the commercial feasibility of optical CIMs remains elusive as the technology requires optical tables, kilowatts of power, and kilometers of optical fibers, which altogether blocks its further development from a proof-of-principle demonstration to a miniaturized commercially viable device.
In SPINTOP, we develop a novel time-multiplexed spinwave Ising machine (SWIM) with artificial spin states implemented via the phase of spinwave radio-frequency (RF) pulses propagating in an Yttrium Iron Garnet (YIG) thin film. It is in principle similar to the optical CIM but operates at orders of magnitude lower frequencies in the microwave domain, which greatly simplifies the peripheral eletronics, and instead of optical pulses uses spin wave pulses, which makes it possible to miniaturize the Ising Machine by orders of magnitude.
