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University of Waterloo Breakthrough Bypasses the “No-Cloning” Barrier
Researchers at the University of Waterloo have achieved a major breakthrough in quantum computing, unveiling the first known method to safely back up quantum information. The discovery offers an elegant workaround to one of the most fundamental constraints in quantum science—the so-called no-cloning theorem—and opens the door to secure, fully quantum cloud storage services.
Quantum computing has long been hailed as a transformative technology, promising dramatic advances in fields ranging from cybersecurity and materials science to medical research and large-scale optimization. Unlike classical computers, which store data as bits that are either 0 or 1, quantum computers use qubits. These qubits can exist in multiple states at once and can be physically realized using electrons, photons, atoms, ions, or even tiny electrical currents.
Governments, universities, and private companies around the world are investing billions of dollars to master the control of qubits and scale them into reliable quantum machines. Yet despite this momentum, a major obstacle has persisted: quantum information cannot be copied in the same way classical data can.
Why the No-Cloning Theorem Matters
At the heart of the challenge lies the no-cloning theorem, a foundational principle of quantum mechanics. It states that it is impossible to make an identical copy of an unknown quantum state. This limitation arises from the delicate nature of quantum information, where observing or measuring a qubit can fundamentally alter its state.
In classical computing, copying information is routine. Files are duplicated for sharing, redundancy, and backups with little thought. In quantum computing, however, the inability to copy data has made tasks such as backup storage and cloud-based services seem nearly impossible.
“For quantum computing to mature into a practical technology, we need ways to securely store and protect quantum information,” said Achim Kempf, professor in the Department of Applied Mathematics at Waterloo and the Dieter Schwarz Chair in the Physics of Information and AI. “This breakthrough is an important step toward building real-world quantum computing infrastructure.”
Encryption as the Key to Quantum Backup
The new method, co-discovered by Kempf and Koji Yamaguchi, sidesteps the no-cloning theorem by combining quantum mechanics with encryption. Rather than attempting to copy raw quantum information directly, the researchers found that encrypted quantum information can be copied safely.
“If we encrypt the quantum information as we copy it, we can make as many copies as we like,” explained Yamaguchi, who developed the technique as a postdoctoral researcher at Waterloo and is now a research assistant professor at Kyushu University. “Once one encrypted copy is decrypted, the decryption key automatically expires. That one-time-use property is what allows us to bypass the no-cloning restriction.”
While the idea of one-time decryption may sound limiting, it is more than sufficient for critical applications. In practice, it enables redundant and encrypted backups of quantum data—precisely what is required for secure quantum cloud services.
Kempf likens the concept to splitting a password between two people. Neither person can access the password alone, but when both parts are combined, the full information is revealed. Similarly, quantum information can be distributed across multiple qubits or servers in such a way that no single copy is usable on its own.
The Power of Quantum Entanglement
The breakthrough also highlights the extraordinary power of quantum entanglement. Individually, a single qubit carries limited information. When qubits are entangled, however, they can share information in ways that grow exponentially.
As Kempf explains, 100 qubits can represent information in 2¹⁰⁰ possible configurations simultaneously—a quantity so vast that it exceeds the storage capacity of all classical computers combined. This shared, non-local information is what makes quantum computing so powerful, but also what makes it so fragile and difficult to manage.
By enabling encrypted duplication, the new method allows researchers to protect this fragile information without violating the fundamental laws of quantum mechanics.
Toward Quantum Cloud Services
The implications of the discovery are significant. Secure quantum backups make it possible to imagine quantum versions of familiar cloud services—such as quantum Dropbox or quantum Google Drive—where sensitive quantum data can be stored redundantly across multiple servers.
Such capabilities are considered essential for the long-term viability of quantum computing, particularly as systems grow larger and more complex. They also strengthen Canada’s position as a global leader in quantum research and commercialization.
The Institute for Quantum Computing at Waterloo, where Kempf is an associate, has already helped launch more than 23 quantum startups focused on sensing, security, and computing, translating fundamental research into real-world applications.
A Milestone for Quantum Science
The research paper detailing the discovery, titled “Encrypted qubits can be cloned,” was published in Physical Review Letters, one of the world’s most prestigious scientific journals.
While many challenges remain before quantum computers become commonplace, this breakthrough removes one of the field’s most persistent roadblocks. By showing that quantum information can be safely backed up—without breaking the rules of quantum mechanics—Waterloo researchers have taken a crucial step toward making quantum computing a practical and resilient technology for the future.
