Table 1.

Comparison of state-of-art Ising computers

	CPU	Quantum annealers	CIM	Mem-HNN	PTNO	SMTJ-based Ising computer
Spin form	Artificial Ising spin	Qubits	Optical parametric oscillator	Memristor	Nano-oscillators	MTJ
Algorithm	Simulated annealing	Quantum annealing	Coherent computing	Modulate intrinsic noise annealing	Simulated annealing	Intrinsic noise annealing + global annealing
Connectivity	All-to-all	Sparse	All-to-all	All-to-all	All-to-all	All-to-all
Room temperature	Yes	No	Yes	Yes	Yes	Yes
Number of nodes solved experimentally (simulated)	4761	61	2000	60	8 (100)	4761
Number of devices (bits)	~109	2048	1 (2048)d	3600	8	80	4096
Power	65 W	25 kW		120 mW	2.56 mWh	Experiment	Simulation using SMTJ in this work	Simulation using SMTJ in ref 45m
						0.64 mWj	0.288 mWl	0.288 mW
Size of the computer (chip)	14 cm2		3$\times {10}^4$ cm3	64 cm2		8 cm2	12288 µm2	12288 µm2
Main frequency	3 GHza		200 kHze	1 MHzg	301 Hzi	10 kHz	10 kHz	1.1 MHz
Time to solution (TSP70)	12 sb	>104 sc	80 msf	320 ms	1.3 × 103 s	40 sk	50.54 s	0.64 s
Energy to solution (TSP70)	780 J	>2.5$\times$108 J		3.84$\times$10−2 J	3.4 J	2.56$\times$10−2 J	1.456$\times$10−2 J	1.8$4\times$10−4 J
Energy efficiency (1/energy to solution)	1.3$\times$10−3	<4.0$\times$10−9		<2.6$\times$101	2.9$\times$10−1	3.9$\times$101	6.8$\times$101	5.4$\times$103

Unavailable quantities are left blank.

^aEstimated average main frequency of Intel Core-i7 PC.

^bSolution time using dataset st70 from ref. ⁷ by using TSP-SAGEP algorithm.

^cApproximation from the result of N = 55 node MaxCut problem.

^d1-km fiber with 2048 pulses per second used as Ising spins in a time-multiplexed way.

^eRound-trip time of 5 µs in experiment.

^fLinear approximation from the simulated result of N = 2000 node complete graph problem. The time of transferring data from FPGA to computer is 60 s×n, where n is the observation time.

^gMain frequency of on-chip computing array using 180-nm CMOS-memristor chip in experiments.

^hEstimated power consumption of main compute kernel.

ⁱEstimated for 80 node system.

^jExperimentally demonstrated power consumption of main compute kernel.

^kExperimentally tested total solution time using dataset st70 from TSPLIB including computing time, data transfer time, and updating time.

^lPower consumption of main compute kernel of 4 Kb SMTJ Ising computer (4-bit bit line) based on the experimentally calibrated SMTJ model.

^mSimulation results using SMTJ with a retention time of 8 ns in ref. ⁴⁵.