Jiuzhang 4.0: A Major Leap for Photonic Quantum Computing
On May 13, a team from the University of Science and Technology of China led by Pan Jianwei, Lu Chaoyang, Zhang Qiang, and Liu Naile, together with multiple partner institutions, published the Jiuzhang 4.0 photonic quantum computing prototype in *Nature*. It is the first system to manipulate and detect the quantum states of 3,050 photons. For Gaussian boson sampling, it is about 10^54 times faster than the world's fastest supercomputer—generating one sample takes just 25 microseconds, whereas a supercomputer would need over 10^42 years.
This is an order-of-magnitude leap for the photonic quantum computing route and re-confirms leadership in this field.
What 3,050 Photons Mean
Think of Jiuzhang 4.0 as a three-dimensional maze with 8,176 exits, through which photons perform extremely complex interference walks.
- 1,024 squeezed quantum states: the high-energy fuel during operation, forming the basis of complex quantum entanglement.
- 8,176 modes: the total number of paths/dimensions photons can traverse.
- 3,050 photons: roughly equivalent to 3,000+ qubits. The previous Jiuzhang 3.0 manipulated only 255 photons, so this is more than a 10x improvement, exponentially expanding the representable computational state space.
- A new benchmark for quantum advantage. Gaussian boson sampling is the standard problem for demonstrating quantum computational advantage. Jiuzhang 4.0's speedup of ~10^54 over El Capitan is among the strongest quantum advantage claims internationally.
- The unique position of the photonic route. Superconducting circuits, ion traps, neutral atoms, and photonics are the four main approaches. Photonics requires no cryogenics and naturally suits certain sampling problems. The Jiuzhang series (2020 → 2.0 in 2022 → 3.0 in 2023 → 4.0 in 2026) has shipped four generations in six years with a steady iteration cadence.
- A stepping stone toward fault-tolerant hardware. Beyond sampling, Jiuzhang 4.0 can generate bosonic error-correcting codes and large-scale entangled cluster states required for fault-tolerant quantum computing. The team's stated next goals: trillion-mode 3D cluster states and future fault-tolerant photonic quantum hardware.
- Practical uses. In the short term, Gaussian boson sampling can be applied to image recognition and graph-theoretic computation; in the long term, it is a component of a universal fault-tolerant quantum machine.
- Jiuzhang 4.0 is a special-purpose analog machine, not a universal computer. Universal quantum computing requires millions of error-corrected qubits—a long road ahead. But the dual lead in scale and low loss leaves room for the fault-tolerant path.
- Compared with the superconducting route (IBM, Google): photonics follows a "sampling advantage + bosonic codes" path, while superconducting follows a "logical qubits + surface code" path. Both are approaching fault tolerance, but their engineering constraints are entirely different.
- For the domestic quantum industry: the Jiuzhang series keeps setting records, and combined with earlier results like 420 km cold-atom entanglement and QuantumCTek progress, photonic quantum tech is producing results from prototypes to network layers.
Why was progress stuck before? The main obstacle to scaling photonic quantum computing is photon loss: the larger and more complex the optical network, the more easily photons get lost, severely degrading computing power.
Jiuzhang 4.0's breakthrough is a programmable spatiotemporal hybrid encoding architecture: photons interfere simultaneously in both time and space, raising network connectivity while keeping the physical device scale in check. The team also built a high-efficiency optical parametric oscillator source, pushing total system efficiency to 51%. The result: sampling in a 102,461-dimensional Hilbert space.