Quantum computers don’t need to be as powerful as we think to break the world’s most secure encryption algorithms, scientists have warned.
A new study claims that quantum computers could render widely used cryptographic security systems obsolete with far fewer qubits, or qubits, than scientists widely predicted, putting sensitive data such as banking information and private messages that were thought to be protected by encryption at risk of being intercepted.
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An example of such a calculation is Shor’s algorithm. Designed by mathematician Peter Scholl in 1994, this quantum algorithm can efficiently factor large numbers. This was the first evidence that quantum computers could theoretically outperform classical computers on practical problems.
Virtually unbreakable by traditional means, it is the basis of RSA public key cryptography and is behind many of the world’s major encryption schemes.
Scientists had previously assumed that defeating Scholl’s algorithm using quantum computers would require a system with millions of qubits. This is very different from today’s best processors, which have only a few hundred qubits. But now a surprising new study, uploaded to the arXiv preprint database on March 31, warns that it may be possible to solve this algorithm in systems with just 10,000 qubits.
Even worse, the authors claim that a quantum computer with just 26,000 qubits could take just seven months to crack RSA-2048 encryption, the industry encryption standard used to secure most digital certificates on the Internet.
Building an error-free quantum computer
Scientists say improvements in the field of quantum error correction (QEC) and increased robustness of neutral-atom quantum computers are behind the shift from systems requiring millions of qubits to just tens of thousands of qubits.
Unlike classical bits, qubits are inherently “noisy” and have a much higher error rate: 1 in a million versus 1 in a thousand. This makes qubits much more likely to fail during calculations, and scientists say that future systems will need millions of qubits, rather than the hundreds built into today’s most advanced systems, to outperform classical computers.
One way to reduce the error rate is to use logical qubits. These are collections of entangled physical qubits that share the same data. This means that if one of the constituent physical qubits fails, the data resides elsewhere and the computation can continue to run uninterrupted.
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The QEC project aims to design qubits and software layers that make quantum computers less prone to errors. This means that fewer qubits are needed in a fault-tolerant system to achieve comparable performance levels.
Neutral atom quantum computers, on the other hand, operate by qubits, which are individual charge-neutral atoms (usually elements such as rubidium, cesium, or ytterbium) that are suspended by a focused laser beam (known as optical tweezers) and cooled to near absolute zero.
Neutral atomic quantum computers are an alternative to traditional superconducting qubits used in processors made by major companies such as IBM, Microsoft, and Google, and the study authors cite these systems as prime candidates for fault-tolerant quantum computing through advances in QEC.
Specifically, a physical qubit can participate in many logical qubits instead of just one, which theoretically reduces the number of qubits required for one logical qubit from hundreds or thousands to just five.
“Recent neutral atom experiments demonstrated universal fault-tolerant operation below error correction thresholds, computation on arrays of hundreds of qubits, and trapping arrays containing more than 6,000 coherent qubits,” the scientists wrote in the research paper, which has not yet been peer-reviewed.
“While major engineering challenges remain, our theoretical analysis shows that properly designed neutral atomic architectures can support quantum computation at cryptographically relevant scales,” they added. “More broadly, these results highlight the power of neutral atoms in fault-tolerant quantum computing in a wide range of scientific and technological applications.”
Solving the most difficult encryption algorithms
In the study, the scientists proposed several new architectures for fault-tolerant quantum computers and analyzed their performance with different error correction mechanisms.
Existing neutral atom machines with 500 qubits and 6,000 qubit arrays both demonstrate “subthreshold” operation. This means that when applying QEC, the error rate decreases exponentially as you increase the number of qubits. Therefore, the larger the system, the more error correction compounds there are to make the quantum computer fault-tolerant. This is the opposite of not applying error correction techniques, where the error rate increases exponentially as the number of qubits in a quantum computer increases.
In this study, researchers estimated the power of existing quantum computing systems and predicted how powerful they would need to be to pose a threat to cryptographic systems. They considered three major cryptographic algorithms. One is Scholl’s algorithm, which is currently the performance benchmark for quantum computing. ECC-256 is a modern but less complex form of encryption used to secure internet traffic and protect cryptocurrencies. and the widely used RSA-2048.
In their research, they showed that without error correction, a state-of-the-art quantum computer would need 1 million qubits per week to crack RSA, but only 500,000 qubits, or tens of minutes, to crack ECC.
Based on the study’s calculations, Scholl’s algorithm is solvable in a system with just 11,961 qubits. A 10,000-26,000 qubit system can crack ECC-256 within 10 days, and an 11,000-14,000 qubit machine can solve RSA-2048 within three years.
The researchers also predicted that a parallel architecture with about 102,000 qubits would be able to break the RSA-2048 cipher within 97 days.
Scientists say that future quantum processors with thousands of logical qubits “will enable a variety of applications with significant scientific and economic value,” but these findings suggest that urgent steps need to be taken to move away from standard cryptography. Google engineers, for example, say the world will transition to post-quantum cryptography within three years.
It is worth noting that this study focuses only on current QEC, leaving open the possibility that smaller systems can achieve the same results if other techniques improve. The scientists noted that increasing the fidelity of physical qubits (designing physical qubits that are inherently less error-prone) or algorithmic compression (further reducing the number of physical qubits required) are among the breakthroughs likely to be achieved in the coming years. This means that the number of qubits needed for future cryptographic destruction systems will be halved.
“These findings have important implications. Although they require considerable expertise, experimental development effort, and architectural design, our theoretical analysis suggests that it is possible to construct neutral atomic systems that can implement Scholl’s algorithm,” the researchers wrote. “This conclusion highlights the importance of continued efforts to transition widely deployed cryptographic systems to post-quantum standards designed to be secure against quantum attacks.”
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