In a development that could eventually reshape digital security, researchers at MIT and the University of Innsbruck have demonstrated a quantum computer that uses just five atoms to factor the number 15—a task that previously required around twelve qubits. The system, described in the journal Science, achieved the correct factors with a confidence level exceeding 99 percent, marking a significant step toward practical quantum computing.
The work directly addresses a challenge set in 1994 by MIT professor Peter Shor, who devised an algorithm capable of finding prime factors of large numbers more efficiently than classical computers. The number 15 is the smallest figure that meaningfully demonstrates Shor's algorithm, and the new system is the first to do so with only five qubits, each represented by a single atom.
What sets this system apart is its potential for scalability. The researchers note that the architecture allows for the addition of more atoms and lasers, which would enable the construction of larger quantum computers. The stability of the system relies on laser pulses that hold the atoms in an ion trap, a technique that can be extended as more components are added.
Why Scalability Matters
Scalability is crucial because it determines whether quantum computers can eventually handle the large numbers used in modern encryption. Current encryption methods, such as RSA, rely on the difficulty of factoring large numbers. If quantum computers can be scaled up, they could potentially break these codes, a prospect that has prompted governments and corporations to explore quantum-resistant cryptography.
Professor Isaac Chuang of MIT, a co-author of the study, emphasized that the demonstration proves Shor's algorithm is realizable in a practical way. "We show that Shor's algorithm, the most complex quantum algorithm known to date, is realizable in a way where, yes, all you have to do is go in the lab, apply more technology, and you should be able to make a bigger quantum computer," he said.
However, Chuang cautioned that building a large-scale quantum computer remains a formidable engineering challenge. "It might still cost an enormous amount of money to build—you won't be building a quantum computer and putting it on your desktop anytime soon—but now it's much more an engineering effort, and not a basic physics question," he added.
Looking Ahead
The team expressed optimism about the future, with Chuang noting that they "foresee it being straightforwardly scalable, once the apparatus can trap more atoms and more laser beams can control the pulses…We see no physical reason why that is not going to be in the cards."
The findings, published in Science, represent a proof-of-concept that could guide future research. While the current system is far from threatening real-world encryption, it provides a clear path forward for building more powerful quantum computers.
Researchers at MIT and the University of Innsbruck have built a five-atom quantum computer that can factor the number 15 with over 99% confidence, demonstrating a scalable approach to quantum computing that could eventually challenge current encryption methods.
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