On December 9th, 2024, Google Quantum AI unveiled its latest quantum chip, Willow, which marks a monumental step forward in the development of quantum computers. Willow is a result of over 10 years of research and innovation, and it solves two of the most fundamental challenges in quantum computing: error correction and performance scaling. Willow demonstrates a significant breakthrough in quantum computing, showcasing major advancements in error correction, scaling, and computational power.
Exponential Error Reduction: A Historic Achievement
One of the most significant challenges in quantum computing has been the high error rate associated with qubits—the fundamental units of computation in quantum systems. Quantum computers are highly susceptible to errors because qubits are extremely sensitive to their environment, leading to information loss during computations. As the number of qubits increases, the error rate typically increases exponentially, making it hard to maintain the quantum nature of the system as it scales. This phenomenon has hindered the practical application of quantum computing for decades.
However, Willow introduces an innovative and successful approach to quantum error correction, breaking through what was once considered an insurmountable barrier. The research team at Google demonstrated that the more qubits they added to Willow’s system, the more they reduced the error rate, instead of seeing it increase. Using a variety of error-correction techniques, they managed to halve the error rate with each incremental increase in the number of qubits, a process known as exponential error reduction.
This achievement is so significant because it demonstrates that quantum error correction can scale effectively with larger qubit arrays, moving quantum systems toward the ability to compute larger and more complex tasks. This milestone is referred to as being “below threshold” in quantum computing, a term that signifies the system can maintain coherence and reduce errors even as the system grows, an essential requirement for building practical, large-scale quantum computers.
For context, quantum error correction had been a key challenge for almost 30 years, dating back to when Peter Shor first introduced the concept of error correction for quantum systems in 1995. The ability to scale up qubits while reducing errors exponentially is a historic accomplishment and a game-changer in quantum technology.
Astonishing Benchmark Performance: A Step Beyond Classical Limits
In addition to the advances in error correction, Willow has demonstrated astonishing computational power, surpassing even the world’s fastest classical supercomputers. The team used the random circuit sampling (RCS) benchmark, a particularly challenging test that assesses whether a quantum computer can perform computations that are intractable for classical systems. This benchmark is considered one of the toughest tasks for quantum computers to solve.
Willow’s performance on the RCS benchmark is nothing short of revolutionary. The quantum chip was able to complete a computation in under five minutes, a task that would take a classical supercomputer 1025 years—a number so vast (10 septillion years) that it exceeds the age of the universe by many orders of magnitude. This difference highlights just how far ahead quantum processors can outperform classical computers in specific areas. Willow’s success on this benchmark reinforces the notion that quantum computing operates on a fundamentally different level of speed and parallelism, capable of solving problems that classical systems could never approach.
The Path to Practical Quantum Computing
While Willow’s performance on benchmarks and error correction is a historic achievement, the ultimate goal of quantum computing is to tackle practical, real-world problems that go beyond what classical computers can solve. Google’s team is keenly aware of this transition, and they are focused on moving from theoretical performance to real-world applications.
For decades, quantum computing has been confined to theoretical demonstrations and small-scale experiments. However, Willow moves us closer to the practical application of quantum computers in fields such as drug discovery, material science, climate modeling, and artificial intelligence. The first stage of this journey involved showing that quantum systems can beat classical systems at certain tasks. The next stage is to demonstrate that quantum systems can solve useful, commercially relevant problems.
Google’s quantum team believes that Willow’s progress provides the foundation for these real-world applications. The team’s next challenge is to demonstrate a “useful, beyond-classical” computation—a quantum computation that solves a practical problem that classical systems cannot address. Willow’s performance brings the team closer to that goal, but significant work remains to ensure that quantum computers can be used for everyday applications in science, business, and technology.
Quantum Error Correction: Real-Time and Beyond
The achievement of reducing error rates exponentially as qubits scale up was accompanied by other significant scientific “firsts.” Willow is one of the first quantum systems to demonstrate real-time error correction. This means that Willow’s error correction is happening continuously during the computation, and any errors are corrected immediately before they can ruin the computation. This real-time correction is vital for large-scale, fault-tolerant quantum computing because, without it, errors would accumulate too quickly for any useful computation to occur.
Moreover, the Willow system has achieved a “beyond breakeven” demonstration, where the lifetime of the logical qubits (the error-corrected qubits) is longer than the individual physical qubits. This milestone is a sign that the error correction is not just preventing failure but actually improving the overall longevity and reliability of the system.
System Engineering: The Backbone of Willow
The success of Willow is not just a result of improved quantum algorithms but also the result of advanced system engineering. Willow was fabricated in a new, state-of-the-art fabrication facility in Santa Barbara, one of the few facilities globally designed specifically for quantum chip production. Building a quantum system involves the integration of various components—such as qubit gates, reset mechanisms, and readout systems—and each of these must work harmoniously. If any component lags or fails to integrate smoothly with the others, the performance of the entire system would degrade.
The system engineering excellence behind Willow ensures that all these components are working together seamlessly, maximizing system performance at every stage. This holistic approach to system design is one of the key reasons Willow has achieved such outstanding results in both error reduction and computational performance.
Quantum Computing: A New Era
The achievement of Willow brings quantum computing closer to fulfilling its immense potential. With exponential improvements in error correction and the ability to vastly outperform classical computers on certain tasks, Willow sets the stage for the future of quantum technologies. While there is still much to be done before quantum computers can perform commercially useful computations, Willow marks the most convincing prototype for a scalable, fault-tolerant quantum computer to date.
Google’s quantum team remains optimistic that, with continued advances, Willow will help drive commercially-relevant quantum algorithms and practical quantum applications. As the field progresses, Willow will play a key role in shaping the future of quantum computing, enabling breakthroughs that were once thought to be impossible.
Willow is a breakthrough in the quantum computing journey, with its ability to exponentially reduce errors as it scales and solve problems that classical supercomputers could never even begin to address. This milestone marks a historic moment in the ongoing quest to unlock the power of quantum mechanics for real-world applications. With Willow, Google has set the stage for the next generation of quantum technologies, promising not only a revolution in computation but also the potential for transforming industries and tackling some of the world’s most pressing challenges.
