Executive Summary
The Story So Far
Why This Matters
Who Thinks What?
Google’s latest quantum processor, named Willow, has achieved a verified speed-up over the world’s most powerful supercomputers, marking a significant step towards practical quantum computing and intensifying concerns about its long-term threat to Bitcoin’s encryption. The breakthrough, detailed in a recent Nature study, demonstrates an experimentally confirmed quantum advantage with real hardware for the first time.
Verified Quantum Advantage
The study, published last Wednesday, reveals that Google’s 105-qubit Willow chip executed a physics algorithm approximately 13,000 times faster than classical simulations could manage. The task, which took Willow just over two hours, would have required roughly 3.2 years on Frontier, one of the world’s fastest publicly benchmarked supercomputers.
Google CEO Sundar Pichai stated on X that the result is verifiable, meaning its outcome can be repeated by other quantum computers or confirmed by experiments. This achievement is considered a significant stride toward the first real-world application of quantum computing.
How the Experiment Worked
Researchers conducted time-reversal experiments on Willow, observing how quantum information spread and refocused across the chip’s qubits. The process involved driving the system forward through quantum operations, disturbing a qubit, and then reversing the sequence to detect an “echo” of information.
This echo, appearing as constructive interference, confirmed quantum behavior in circuits too complex for classical computers to simulate precisely. Willow’s superconducting transmon qubits maintained high stability, enabling 23 layers of quantum operations across 65 qubits, surpassing current classical simulation capabilities.
Evolution of Quantum Processors
Unveiled in December 2024, Willow is Google’s most recent superconducting quantum processor, designed for enhanced stability and verifiability compared to its predecessors. It builds upon the 2019 Sycamore experiment, which demonstrated quantum supremacy but lacked consistent reproducibility.
Willow addresses this by incorporating improved error correction, allowing qubits to remain coherent for longer periods. This enables repeatable and verifiable experiments within the same device, transitioning quantum interference from theoretical concept to testable engineering.
Implications for Bitcoin
While Willow’s current capabilities do not pose an immediate threat to encryption, its verified progress signals a steady march toward quantum machines capable of breaking existing cryptographic standards. Bitcoin and other digital assets rely on elliptic-curve cryptography, which is currently impervious to classical computers but theoretically vulnerable to sufficiently powerful quantum systems.
Christopher Peikert, a professor of computer science and engineering at the University of Michigan, noted that quantum computation has a reasonable, albeit distant, probability of posing an “existential” long-term risk to cryptocurrencies. He emphasized that the technology still requires significant advancement before it can threaten modern cryptography in the next few years.
Transitioning to post-quantum signature schemes would involve trade-offs, such as larger keys and signatures. Peikert explained that this would significantly increase network traffic and block sizes for cryptocurrencies that depend on numerous signatures for transactions.
The Quiet Countdown
The vast performance gap—two hours for Willow versus several years for a supercomputer to simulate its circuits—represents the clearest experimental proof of device-level quantum advantage to date. This development underscores that post-quantum security is no longer a distant concern but an approaching challenge for cryptographers and developers in the digital asset space.
