A 1024-Spin Scalable Ising Machine With Capacitive Coupling and Progressive Annealing Method for Combination Optimization Problems

A range of quantum-, optical- and CMOS-based approaches have been explored to solve Nondeterministic polynomial-time hard (NP-hard) combinatorial optimization problems (COPs), of which we consider ring oscillator (ROSC) coupled Ising machine to be highly prospective. This brief proposed a scalable ROSC-based Ising machine with capacity coupling and phase drift eliminator. The coupling module consisting of two MOSCAPs and several switch transistors allows for nine coupling strengths, which can be arbitrarily configured into different weight resolutions, and shows resilience to capacitance variations. Phase drift eliminator was designed to alleviate the effect of intrinsic noise within the ROSC array, which ensures accurate readout of the spin state. The area of the readout circuit is only 32% of the previous phase-sampling circuit. We also proposed a progressive annealing method inspired by quantum adiabatic annealing, which is easy to perform on ROSC-based Ising machines and does not require additional random number generators. After applying the progressive annealing method, accuracy can be achieved up to 98% for randomly generated contentious problems.