Quantum Hardware Database
NTT 100,512-Spin Coherent Ising Machine
NTT's coherent Ising machine (CIM) is an optical computer that uses 100,512 pulses of light circulating in a 5-kilometer fiber ring as artificial spins to solve optimization problems. Reported in Science Advances in 2021, it was the largest Ising machine of its kind and found good max-cut solutions about 1,000 times faster than simulated annealing on a CPU.
Qubit Count
100,512
Qubit Type
Optical parametric oscillator pulses acting as Ising spins (not gate-model qubits)
Architecture
Fiber-ring coherent Ising machine with measurement feedback and an FPGA-based matrix multiplier
Released
2021
Gate Error (2Q)
Not applicable: it is an Ising solver, not a gate-based computer; solution quality is measured by the energy of the answers it finds
Coherence Time
Not applicable in the gate-model sense; each pulse is created and measured over a 25-microsecond round trip in a 5-kilometer fiber ring
Operating Temp
Room temperature optics and electronics (some detectors and the pump laser system need standard laboratory conditions)
Cloud Access
Not publicly available
Company
NTT
Overview
The coherent Ising machine is one of the strangest and most interesting computers in this database. It does not use qubits or gates. Instead, a laser produces a long train of light pulses, and each pulse acts like one spin in an Ising model, a mathematical model for magnetism that can also represent many optimization problems. The pulses travel around a ring of optical fiber, interact through a clever electronic feedback loop, and settle into a configuration that is a good answer to the problem.
NTT and its collaborators reported in 2021 that they had scaled this idea to 100,512 spins, which is far larger than any quantum annealer's qubit count. The paper describing it was published in Science Advances in September 2021.
History and background
The coherent Ising machine was developed by researchers in Japan, including Yoshihisa Yamamoto's group and NTT's Basic Research Laboratories, with partners in the ImPACT program supported by the Japanese government. In 2016, two papers in Science reported a 100-spin fully programmable machine with all-to-all connections and a 2,000-node machine that solved max-cut problems on a 2,000-node complete graph in less than a ten-thousandth of a second. That 2,000-spin machine was later opened to public users through a cloud service for a time.
In 2021 NTT, the National Institute of Informatics, Osaka University, the University of Tokyo, and Stanford University extended the machine to 100,512 spins by lengthening the fiber ring to 5 kilometers and building a custom matrix-multiplication system. The team reported that it was about 1,000 times faster than simulated annealing running on a CPU for finding approximate solutions to the max-cut problem on a 100,000-node complete graph.
How it works
The heart of the machine is a ring of optical fiber about 5 kilometers long, in which light takes about 25 microseconds to circulate. A pump laser creates tens of thousands of short pulses in a nonlinear crystal, each of which becomes a degenerate optical parametric oscillator pulse. Above a threshold, each pulse builds up in one of two phases, 0 or pi, and these two states represent spin up and spin down.
To make the spins interact, the machine uses measurement feedback. At every round trip, the amplitude of each pulse is measured, and the results go into an electronic circuit that multiplies the vector of measurements by the matrix of couplings that defines the problem. The product tells each pulse how strongly to nudge its partners on the next circulation, and the nudge is injected back as an optical signal. For 100,512 spins this requires multiplying a 100,512 by 100,512 matrix by a vector in 25 microseconds, which needs about 1,000 trillion operations per second and 100 terabytes per second of memory bandwidth, so NTT built a custom parallel system.
Because the pulses are quantum optical objects, the machine's dynamics near the threshold may include squeezing and entanglement-like effects that help it explore many configurations before settling. Researchers continue to study whether these quantum features give the machine an advantage over classical solvers, and the question is not settled.
Connectivity
All-to-all: measurement-feedback couplings link every pair of the 100,512 spins
Specifications in detail
| Item | Detail |
|---|---|
| Published | Science Advances, September 2021 |
| Spins | 100,512 degenerate optical parametric oscillator pulses |
| Couplings | About 10 billion (all-to-all) |
| Fiber ring | 5 kilometers; one round trip takes about 25 microseconds |
| Feedback computation | About 1,000 tera-operations per second for the matrix-vector product |
| Earlier machine | 2,048-pulse CIM in a 1-kilometer ring (Science, 2016) |
Key features
- 100,512 optical spins with 10 billion couplings
- All-to-all connectivity from measurement feedback
- About 1,000 times faster than CPU-based simulated annealing on a 100,000-node max-cut problem
- Room-temperature operation
- Built by NTT with NII, Osaka University, the University of Tokyo, and Stanford University
Limitations
- It solves Ising-type optimization problems only and is not a universal quantum computer
- Whether it provides a genuine quantum advantage over the best classical heuristics is debated
- The 100,000-spin machine is a research instrument, not a general commercial product
- It needs a 1,000 tera-operations-per-second matrix multiplier to implement all-to-all feedback
Timeline
| When | What happened |
|---|---|
| 2014 | Time-multiplexed degenerate optical parametric oscillator networks are shown to act as a coherent Ising machine. |
| 2016 | A 100-spin machine with all-to-all connections and a 2,000-node machine are reported in Science. |
| 2017 | A 2,000-spin CIM is opened to public users through a cloud service for a period. |
| September 2021 | The 100,512-spin coherent Ising machine is reported in Science Advances. |
| 2022 onward | Follow-up work explores independent set problems, sampling, and the quantum critical behavior of the machine. |
What it is used for
- Max-cut and other graph optimization problems
- Finding independent sets in large graphs
- Combinatorial problems in communications, logistics, and finance that map to Ising models
- Studying quantum criticality in optical oscillator networks
How it compares
- Compared with D-Wave Advantage2, which has about 4,400 qubits with limited connectivity, the CIM has about 100,000 spins with all-to-all connectivity, but both solve Ising problems.
- Compared with gate-based machines like Willow or Heron, the CIM cannot run general algorithms, and its spin count is not comparable to qubit counts.
- Compared with Xanadu Borealis, both use light, but Borealis samples a quantum distribution while the CIM solves optimization problems.
Technical notes
A degenerate optical parametric oscillator (DOPO) produces a pulse whose phase can be either 0 or pi, which corresponds to the two states of an Ising spin. In a CIM, pulses circulate in a fiber ring, and after each trip their amplitudes are measured, multiplied by the problem's coupling matrix in electronics, and fed back to adjust the next round. The network then settles into a low-energy configuration that represents a good solution.
Why it matters
The CIM shows that special-purpose physical machines can address large optimization problems today, with sizes far beyond the reach of present gate-based hardware. It is also a reminder that quantum computing is a family of approaches that includes analog, optical, and hybrid machines.
The honest caveat is that an advantage over the best classical heuristics has not been conclusively shown. NTT's own comparison is against simulated annealing, a baseline that sophisticated classical solvers often beat, so independent benchmarking matters.
Frequently asked questions
Is the coherent Ising machine a quantum computer?
It is an optical machine whose dynamics may involve quantum effects, but it is not a universal quantum computer. It solves Ising optimization problems.
How many spins does it have?
100,512 optical pulses, each acting as an Ising spin, with all-to-all couplings.
Why is the fiber ring 5 kilometers long?
The long ring holds more than 100,000 pulses at once. The electronics have 25 microseconds, the round-trip time, to compute the feedback for every pulse.
Can I use it?
The 100,512-spin machine is a research instrument. An earlier 2,000-spin version was made available to public users through a cloud service, and NTT has also offered Ising-solver services; check NTT for current options.
Does it beat classical computers?
It found approximate max-cut solutions about 1,000 times faster than simulated annealing on a CPU, but better classical heuristics exist, so a general quantum advantage is not established.
Keep exploring
- Related processor: D-Wave Advantage2
- Related processor: Xanadu Borealis
- Related processor: Pasqal Fresnel (Orion generation)
This profile is written for educational purposes and summarizes company announcements, published papers, and vendor specification sheets. Last reviewed: September 30, 2026. Figures marked as company-reported have not all been independently verified, and benchmarks differ between vendors, so compare them with care.