A powerful quantum computer has once again claimed to reach quantum advantage, performing a task that would take today’s fastest supercomputers longer than the lifetime of the universe. While this milestone highlights impressive progress, it also raises important questions: how close are we to building practical, useful quantum machines?
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What Is Quantum Advantage?
Quantum advantage occurs when a quantum computer solves a problem beyond the reach of classical computers. It does not necessarily mean that the task is useful in the real world—it simply proves that quantum mechanics can outperform traditional computation under certain conditions.
The latest breakthrough comes from Jiuzhang 4.0, a photonic quantum computer developed by Chao-Yang Lu and his team at the University of Science and Technology of China. Instead of using superconducting circuits or trapped ions like other quantum systems, Jiuzhang performs calculations using photons—particles of light—manipulated through an intricate network of mirrors and beam splitters.
Jiuzhang 4.0 Sets a New Record
The researchers employed Jiuzhang for a specialized task called Gaussian Boson Sampling (GBS). In this process, photons are sent through the machine, and their output states are measured after traveling through a maze-like optical setup. GBS is extremely challenging for classical computers to simulate because of the complexity and randomness of quantum interference.
Previous attempts at GBS involved fewer than 300 photons. Jiuzhang 4.0 shattered that record by handling 3,090 photons—a tenfold leap forward. To put this in perspective, Lu’s team calculated that simulating the same experiment on the world’s fastest supercomputer would take 10⁴² years. Jiuzhang, by contrast, completed the task in just 25.6 microseconds.
Quantum researchers worldwide quickly acknowledged the significance of the achievement. Jonathan Lavoie of the Canadian startup Xanadu, which previously held a GBS record of 219 photons, called it an “impressive technical achievement.” Chris Langer from Quantinuum, another leading quantum firm, agreed: “It is important that quantum systems can prove they are not simulable.”
The Ongoing Battle Between Quantum and Classical Machines
This is not the first time Jiuzhang has claimed quantum advantage. Earlier versions also produced results that seemed impossible for classical computers to match. However, in each case, new algorithms on traditional machines eventually closed the gap, replicating Jiuzhang’s results in a fraction of the expected time—sometimes in under an hour.
Bill Fefferman, a computer scientist at the University of Chicago who helped develop one of these breakthrough classical algorithms, highlights the challenge. Photonic quantum computers are prone to photon loss—many photons vanish or get miscounted as they pass through the optical maze. This noise makes the system less reliable. “Here, they reduced their rates of noise, and at the same time made the experiment larger, which seems to cause our algorithm to struggle,” Fefferman explained.
Still, noise remains an issue. The current Jiuzhang machine, though improved, is not immune. Experts believe future classical algorithms may once again undermine the claim of quantum advantage.
Why Quantum Advantage Isn’t Enough
While Jiuzhang’s achievement is groundbreaking from a physics perspective, its practical relevance remains debatable. Jelmer Renema of the University of Twente warns: “They are not in the regime yet where we can be confident that no classical strategy is possible.”
In other words, quantum advantage in a narrow benchmark does not guarantee a path to useful computation. Fefferman describes the dynamic as a “virtuous cycle”: every time quantum machines advance, classical computers catch up, helping scientists better understand the boundary between the two realms. For science, this back-and-forth is invaluable. For industry, however, it doesn’t yet translate into direct applications.
Gaussian Boson Sampling: A Benchmark, Not a Solution
Experts agree that GBS is more of a benchmark than a practical tool. It demonstrates the difference between quantum and classical systems but does not solve meaningful problems for society. Nicolás Quesada at Polytechnique Montréal points out the difficulty in proving that GBS is “smoking-gun evidence” of quantum advantage. Even if Jiuzhang excels at GBS, that doesn’t automatically make it suitable for chemistry simulations, financial modeling, or other real-world applications.
Specialization Limits Photonic Quantum Computers
Another limitation lies in Jiuzhang’s design. Unlike general-purpose quantum computers under development by companies like Google, IBM, and Quantinuum, Jiuzhang is highly specialized. It cannot be programmed to perform a wide range of tasks. As Lavoie emphasizes: “While it may demonstrate computational advantage for a narrow task, it lacks crucial elements for fault-tolerant and useful quantum computation.”
Fault tolerance—where a quantum machine automatically detects and corrects its own errors—is considered the holy grail of quantum computing. Without it, scaling up to practical, reliable applications remains out of reach.
Potential Applications of Jiuzhang’s Power
Despite its limitations, Jiuzhang’s extraordinary capability in GBS could inspire useful applications. Lu and his team suggest that the process may enhance computations in:
- Quantum chemistry, allowing researchers to analyze molecular structures more efficiently.
- Machine learning, particularly in solving certain mathematical problems where randomness and high-dimensional data are key.
Fabio Sciarrino at Sapienza University of Rome believes this photonic approach could open a new paradigm. By developing light-based quantum computers, researchers may eventually build systems uniquely suited for machine learning tasks.
Frequently Asked Questions:
What does it mean when a quantum computer achieves quantum advantage?
Quantum advantage means a quantum computer performs a task that is practically impossible for the most powerful classical supercomputers. It shows quantum systems can outperform traditional machines under specific conditions.
How did Jiuzhang 4.0 achieve quantum advantage?
Jiuzhang 4.0, a photonic quantum computer from China, achieved quantum advantage by performing Gaussian Boson Sampling with over 3,000 photons—far beyond the reach of current classical algorithms.
Why is Gaussian Boson Sampling important in quantum computing?
GBS is not a practical problem-solving tool but a benchmark that highlights the computational differences between quantum and classical systems. It helps researchers test the boundaries of quantum mechanics in computation.
Does quantum advantage mean quantum computers are ready for real-world use?
Not yet. While quantum advantage is an impressive milestone, most demonstrations focus on narrow, specialized tasks. Practical quantum computers must still achieve fault tolerance and programmability to solve everyday challenges.
What are the limitations of Jiuzhang 4.0?
Jiuzhang is highly specialized for photonic experiments and cannot be programmed for general-purpose tasks. It also suffers from noise and photon loss, limiting its reliability for practical applications.
Can classical computers still catch up to Jiuzhang’s results?
Yes. In the past, new algorithms allowed classical computers to replicate Jiuzhang’s achievements faster than expected. Experts believe further advances in classical computing could challenge its current claims.
What are potential applications of Jiuzhang’s capabilities?
Although GBS itself is not practical, Jiuzhang’s methods may eventually support breakthroughs in machine learning, chemistry simulations, and image recognition. These remain early-stage possibilities.
Conclusion
The achievement of quantum advantage by Jiuzhang 4.0 represents a remarkable step in the journey of quantum computing. By processing over 3,000 photons in a fraction of a second, the photonic system demonstrates capabilities far beyond even the world’s fastest supercomputers. Yet, this milestone does not signal that practical, general-purpose quantum computers are ready. Limitations such as noise, photon loss, and lack of fault tolerance still stand in the way of widespread application. Even so, each breakthrough fuels progress—pushing researchers to refine hardware, invent smarter algorithms, and expand the boundary between classical and quantum computation. Whether Jiuzhang’s feat holds up against future classical advances or not, it deepens our understanding of what quantum systems can achieve.
