A specific mathematical problem that would take the world's fastest supercomputer approximately 10^42 years to solve has been cracked by China's latest "Jiuzhang-4" quantum computing prototype in just 25 microseconds, representing a speed increase of over one hundred trillion trillion trillion trillion times.
A research team from the University of Science and Technology of China, led by Pan Jianwei, Lu Chaoyang, Zhang Qiang, and Liu Naile, in collaboration with several domestic research institutions, has successfully developed the programmable quantum computing prototype "Jiuzhang-4." This system utilizes 1,024 squeezed-state inputs and operates across 8,176 modes. For the first time, it has manipulated and detected a quantum state comprising up to 3,050 photons, setting a new world record in photonic quantum information technology. The findings were published in the prestigious international academic journal *Nature* on the 13th.
What is a quantum computer, and how does it differ from the computers we use daily? What makes "Jiuzhang-4" so powerful, and what are the implications of this achievement?
**Q: What is a quantum computer?** A: A quantum computer is a physical device that performs high-speed mathematical and logical operations, as well as stores and processes quantum information, by adhering to the laws of quantum mechanics. Unlike classical bits in conventional computing, which are either "0" or "1," quantum computers use quantum bits (qubits). Qubits can exist in a superposition of both "0" and "1" states simultaneously. Leveraging superposition and entanglement, quantum computing can process a vast number of computational pathways in parallel, achieving exponential speedups for specific problems.
The leading technological approaches for qubits include superconducting circuits, ion traps, photonics, and neutral atoms. "Jiuzhang-4" is a photonic quantum computing prototype. It encodes qubits using photons and executes quantum computations through the manipulation and measurement of these photons. It represents a significant upgrade from its predecessors: "Jiuzhang" (2020), "Jiuzhang-2" (2021), and "Jiuzhang-3" (2023).
**Q: What do the terms "1,024 squeezed states," "8,176 modes," and "3,050 photons" mean?** A: The "1,024 squeezed states" can be understood as the "high-energy fuel" for this quantum computer's operation. In photonic quantum computing, squeezed-state photons possess unique quantum properties that form the foundation for building complex quantum entanglement.
The "8,176 modes" refer to the total number of "paths" or "dimensions" through which photons can travel within the computational network. Imagine a super three-dimensional maze with 8,176 exits, where photons undergo extremely complex interference patterns as they navigate.
The "3,050 photons" correspond to over 3,000 qubits. Previously, "Jiuzhang-3" manipulated and detected 255 photons. "Jiuzhang-4" has increased this number by more than tenfold, indicating an exponential growth in the computational state space the system can represent and process. This marks a quantitative leap forward in humanity's ability to manipulate the microscopic quantum world.
**Q: What is the key technological breakthrough of "Jiuzhang-4"?** A: Scaling up photonic quantum computing has long been hindered by a major obstacle known as "photon loss." As optical networks become larger and more complex, photons are highly prone to being lost, significantly weakening computational power.
The primary breakthrough lies in the team's innovative "programmable spatiotemporal hybrid encoding" architecture. Previously, scaling up required simply adding more optical components, leading to bulky devices with high loss rates. "Jiuzhang-4" enables photon interference to occur simultaneously in both the time and space dimensions. This greatly enhances the overall connectivity of the network while effectively controlling the physical scale of the device. Consequently, it achieves the ability to manipulate and detect up to 3,050 photons, resulting in an exponential increase in computational power.
**Q: What are the implications of this achievement?** A: Currently, the "Jiuzhang" series represents an extremely powerful specialized quantum simulator. It excels at solving specific mathematical problems like "Gaussian boson sampling." In the short term, this problem has applications in areas such as image recognition and graph theory calculations. In the long term, it can be used to generate bosonic error-correcting codes, which are crucial for building future high-stability, general-purpose quantum computers.
The dual advantages of scale and low loss demonstrated by "Jiuzhang-4" pave the way for constructing a "three-dimensional cluster state with a trillion quantum modes" and future "fault-tolerant photonic quantum computing hardware." This lays a solid foundation for the eventual realization of a general-purpose quantum computer.
Achieving a general-purpose quantum computer will require the manipulation of millions of qubits along with robust error-correction capabilities. These goals will necessitate continuous iteration and gradual advancement based on existing quantum computing prototypes.
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