Combinatorial optimization problems are known for being particularly hard to solve on traditional von Neumann architectures. This has led to the development of Ising Machines (IMs) based on quantum annealers and optical and electronic oscillators, demonstrating speed-ups compared to central processing unit (CPU) and graphics processing unit (GPU) algorithms. Spin torque nano-oscillators (STNOs) have shown GHz operating frequency, nanoscale size, and nanosecond turn-on time, which would allow their use in ultrafast oscillator-based IMs. Here, we show using numerical simulations based on STNO auto-oscillator theory that STNOs exhibit fundamental characteristics needed to realize IMs, including in-phase/out-of-phase synchronization and second harmonic injection locking phase binarization. Furthermore, we demonstrate numerically that large STNO network IMs can solve Max-Cut problems on nanosecond timescales.
This is the accepted version of a paper published in IEEE transactions on magnetics. This paper has been peer-reviewed but does not include the final publisher proof-corrections or journal pagination.
In this work, a novel magnetic field-to-digital converter based on emerging spin-torque nano-oscillators (STNOs) is proposed. The architecture is inspired by voltage controlled oscillator (VCO)-based analog-to-digital converters (ADCs) which have shown inherent first-order noise shaping of both quantization-and phase-noise without the need for feedback. In the proposed architecture, the STNO acts both as a magnetic field sensor and VCO. The architecture's performance is evaluated in terms of signal-to-noise and distortion ratio (SNDR) utilizing Verilog-AMS modeling, where a macrospin model fitted to experimental data is employed for accurate description of the STNO operation. The presented simulation results demonstrate the potential of the STNO-based magnetic field-to-digital converter architecture.
Ising Machines (IMs) have the potential to outperform conventional Von-Neuman architectures in notoriously difficult optimization problems. Various IM implementations have been proposed based on quantum, optical, digital and analog CMOS, as well as emerging technologies. Networks of coupled electronic oscillators have recently been shown to exhibit characteristics required for implementing IMs. However, for this approach to successfully solve complex optimization problems, a highly reconfigurable implementation is needed. In this work, the possibility of implementing highly reconfigurable oscillator-based IMs is explored. An implementation based on quasiperiodically modulated coupling strength through a common medium is proposed and its potential is demonstrated through numerical simulations. Moreover, a proof-of-concept implementation based on CMOS coupled ring oscillators is proposed and its functionality is demonstrated. Simulation results show that our proposed architecture can consistently find the Max-Cut solution and demonstrate the potential to greatly simplify the physical implementation of highly reconfigurable oscillator-based IMs.
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