Google says it has turned one of the most promising concepts in quantum computing into a technology that can actually run on chips.

Google Quantum’s AI team published a paper on Science on Thursday, stating that a technique called “magic state cultivation” magic state cultivation reduced the error rate by about 40 times on their Willow processors.

Making quantum computers more affordable is of great importance not only for physics laboratories, as it would bring forward the day when they can perform useful tasks such as designing drugs and new materials, but it would also bring us one step closer to potentially cracking the encryption that protects bank login information and Bitcoin wallets.

Quantum computers operate based on quantum bits ( qubit ) – quantum bits can exist in a superposition state of both 0 and 1 simultaneously, allowing the machine to explore many answers in parallel. However, they are also extremely fragile: a small amount of heat or electrical noise can flip a quantum bit and ruin the computation. Therefore, the entire industry is focused on error correction, which involves distributing information across multiple quantum bits in order to detect and correct errors.

Error correction can handle simple calculations well, but truly useful programs require a different type of more complex calculations, which cannot be protected in the same way. To perform these calculations, the machine must first create a "magical state"; they are like disposable fuel cells for these calculations: each magical state is consumed the moment it is used.

Google claims that producing a clean quantum state has always been extremely costly. According to Google, some estimates suggest that this process could consume up to 95% of the total capacity of a quantum computer, leaving very limited space for actual computations.

Physicists Sergei Bravyi and Alexei Kitaev proposed a standard solution as early as 2004 – Magic State Distillation ( magic state distillation ), which involves purifying many noisy magic states into a few clean magic states. This method is effective, but it requires massive quantum bit “factories”, which do nothing else but this task.

In 2024, Google researchers proposed a cheaper approach, which they named "magic state cultivation." Unlike factories, this technique is more akin to a filter: a rough "magic state" is injected into a very small area of the chip, and then a series of checks are performed. Each attempt that is found to be defective is discarded, leaving only the survivors that continue to "grow." The paper even suggests that further refinement "may never be necessary in practice."

Google stated: "On Google Quantum's AI Willow processor, our protocol achieved an astonishing 40-fold reduction in error compared to the untrained state. We also obtained the T-state, with a logical fidelity record of 99.99%."

Only about 8% of the attempts pass all checks, which means that the chip discards more than nine-tenths of the attempts in order to maintain a clean state.

Cultivating technology is one of the key techniques in Gidney's estimates for 2025. This estimate suggests that RSA-2048 encryption can be cracked using less than 1 million noisy quantum bits, which is a 20-fold reduction from the 20 million estimated in 2019. Prior to this experiment, cultivating technology had only been tested in theory and computer simulations.

In March, Google further tightened this estimate. At that time, a white paper co-authored by Google's quantum researcher AI, Ethereum Foundation researcher Justin Drake, and Stanford cryptographer Dan Boneh stated that the cost of cracking Bitcoin's elliptic curve cryptography was less than 500,000 physical quantum bits. Elliptic curve cryptography is a mathematical mechanism that prevents anyone from deriving private keys from public addresses. This result builds upon Google's experiment in October last year Quantum Echoes – which was the first verified quantum acceleration on real hardware.

However, this does not mean that someone is stealing wallets. In this experiment, at most 54 out of Willow 105 quantum bits were used, and the paper points out that to break down a RSA-2048 key, a magic state with an error of about one part in a trillion is required, which is approximately a million times cleaner than the level just achieved by Google.

Google stated that the next step is to scale up the development of this technology. The team expects that if the underlying hardware noise of Willow is reduced by half, the magic-state error will drop to about two in a hundred thousand, as the errors in this process decrease with the cube of the chip's noise level.