Google Says It Just Cracked One of Quantum Computing's Biggest Bottlenecks
In brief
- Google Quantum AI said Thursday that a technique called magic state cultivation cut errors about 40-fold on its Willow chip, producing magic states with 99.99% fidelity.
- Magic states are single-use resources needed to run useful quantum programs, and Google says some estimates put the cost of making them at up to 95% of a quantum computer's capacity.
- Cultivation is one of the tricks behind Google's 2025 estimate that RSA-2048 encryption could fall to under a million noisy qubits, though code-breaking would need magic states with errors near one in 10 billion.
Google says it has turned one of quantum computing's most promising paper tricks into something that actually works on a chip.
In a paper published in Science on Thursday, the company's Quantum AI team showed that a technique called magic state cultivation cut errors by about 40 times on its Willow processor.
Making quantum computers cheaper to build matters far beyond physics labs, because it brings forward the day they do useful work, like designing drugs and new materials, and also the day one could break the encryption that protects bank logins and Bitcoin wallets.
Quantum computers run on qubits—quantum bits that can hold a blend of 0 and 1 at once, letting them explore many answers in parallel. They are also absurdly fragile: a little heat or electrical noise can flip a qubit and wreck a calculation, which is why the whole industry is obsessed with error correction (spreading one piece of information across many qubits so mistakes can be caught and fixed).
Error correction handles the simple operations well, but a genuinely useful program also needs a class of harder operations that can't be protected the same way. To run them, the machine first has to manufacture magic states, which work like single-use fuel cells for those operations: each one is consumed the moment it's used.
Producing clean magic states has always been brutally expensive. Some estimates put the bill at up to 95% of a quantum computer's entire capacity, according to Google, leaving very little room for the actual computing.
Physicists Sergei Bravyi and Alexei Kitaev laid out the standard fix in 2004 with magic state distillation, which takes many noisy magic states and boils them down into a few clean ones. It works, but it demands sprawling qubit "factories" that do nothing else.
→In 2024, Google researchers proposed a cheaper route they named magic state cultivation. Instead of a factory, this technique behaves like a filter, injecting a rough magic state into a tiny patch of the chip to then run a chain of checks on it, throw out every attempt with a detected flaw, and keep growing the survivors. Their paper went as far as suggesting further distillation "may never be needed in practice."
“On Google Quantum AI's Willow processor, our protocol achieved an extraordinary 40-fold reduction in errors relative to un-cultivated states. And we got T-states with a record logical fidelity of 99.99%,” Google said.
Only about 8% of attempts passed every check, meaning the chip discards more than nine out of every 10 tries to keep one clean state.
Cultivation is one of the tricks behind Gidney's 2025 estimate that RSA-2048 encryption could be broken with under a million noisy qubits, a 20-fold drop from the 20 million he estimated in 2019. Until this experiment, cultivation had only been tested in theory and computer simulations.
Google kept tightening the screws in March, when a Quantum AI whitepaper co-authored with Ethereum Foundation researcher Justin Drake and Stanford cryptographer Dan Boneh put the cost of breaking Bitcoin's elliptic curve cryptography (the math that stops anyone from deriving your private key from your public address) at fewer than 500,000 physical qubits. That follows the company's Quantum Echoes experiment last October, the first verified quantum speedup on real hardware.
Nobody is draining wallets with this. The experiment used at most 54 of Willow's 105 qubits, and the paper notes that factoring an RSA-2048 key would require magic states with errors around one in 10 billion, roughly a million times cleaner than what Google just achieved.
Google says the next step is running cultivation at a larger scale. The team projects that halving Willow's underlying hardware noise would push magic state errors down to about two in 100,000, because errors in the process shrink with the cube of the chip's noise level.
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