  Ising computer is a powerful computation scheme to deal with NP-hard
optimization problems that cannot be efficiently addressed by conventional
computers. A robust probabilistic bit (P-Bit) which is realized by a hardware
entity fluctuating in time between -1 and 1 plays a key role in the success of
Ising computer. Spintronics technology, such as stochastic nanomagnet, is
recently proposed as a good platform for the hardware emulation of P-Bit. Here,
we report, for the first time, a Time Division Multiplexing (TDM) Ising
computer using single tunable true random number generator which is comprised
of a Spin Torque Nano-Oscillator (STNO). First, the intrinsic frequency
fluctuation of the STNO is utilized to design a simple digital true random
number generator (TRNG). The true random number generator is further evolved
into a tunable random number generator to act as a P-Bit. Second, in order to
accomplish combinational optimization with our proposed P-Bit under Ising
model, a novel incremental coupling rule is proposed. With such coupling rule
between P-Bit array, high fidelity NOT and XOR logic gate is demonstrated.
Third, it is proposed that our digital TRNG can be simply reused acting as a
P-Bit array by time division multiplexing. The whole Ising computer can be
implemented by one single STNO, and integer factorization of as high as 87%
accuracy rate is achieved.
