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Researchers Enable Secure Data Retrieval from Single Server Using NISQ Devices

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October 2, 2026 by Ivy Delaney

Protecting sensitive data during remote access remains a key challenge in cryptography; existing methods often require multiple servers or rely on unproven computational assumptions. Symmetric private information retrieval now allows secure extraction of single bits without revealing their location, using only a single server and today’s noisy intermediate-scale quantum (NISQ) devices. This breakthrough overcomes a long-standing barrier previously considered impossible for parties with unrestricted quantum capabilities.

A new method for secure data retrieval uses quantum technology with only one server, overcoming previous limitations suggesting such single-server private information retrieval was impossible when facing powerful adversaries. The advancement relies on noisy intermediate-scale quantum (NISQ) devices, today’s early generation of quantum computers, which lack long-term quantum memory and immediately measure received qubits. Researchers at the University of Toronto and The University of Hong Kong have achieved a breakthrough in secure data retrieval with implications for cloud computing and confidential databases.

Symmetric private information retrieval allows extraction of single bits of data without revealing their location, using only today’s limited noisy intermediate-scale quantum (NISQ) devices and a single server; previously considered impossible when facing powerful adversaries. This advancement relies on encoding information onto individual photons, much like sealing letters with wax to detect tampering, before transmitting them via a quantum channel.

Information-theoretic security underpins this new method by use of the fundamental laws of physics instead of mathematical complexity. The team overcame limitations stemming from the inability of current quantum computers to store qubits for extended periods; each received photon is measured immediately.

Quantum privacy attained via photonics surpasses classical limitations

Database privacy exceeding 10-6 was achieved for a 104-bit database; this represents an improvement over prior methods which necessitated either multiple databases or reliance on unproven computational assumptions to attain comparable security levels. Encoding data onto photons and utilising BB84 states alongside random permutation into blocks effectively scrambles the data to prevent eavesdropping.

Minimal additions to existing equipment are required for implementation, specifically passive linear-optical measurement employing one ancillary mode is sufficient. Approximately one thousand qubits constitute a suitable block length for secure operation with their 104-bit database; this figure directly correlates to achieving a privacy level exceeding 10-6 against potential eavesdroppers attempting to discern information from the data itself.

Simulations demonstrate that the established security bound remains nearly tight, indicating minimal wasted resources in practical application and validating protocol efficiency under realistic conditions. Furthermore, the method extended database privacy to encompass decoy-state weak coherent pulses, a technique used to mitigate photon loss during transmission, showing adaptability beyond ideal single-photon sources.

Secure database access via symmetric private information retrieval utilising near-term quantum processors

This demonstration offers a potential route towards strengthening data security in an era where cloud computing and vast databases are increasingly vulnerable; however, immediate measurement requirements currently present a practical hurdle for wider adoption. Noisy intermediate-scale quantum (NISQ) devices necessitate this approach due to their limited ability to store qubits reliably, yet it clashes with emerging architectures exploring longer coherence times, devices that *can* retain quantum information for extended periods.

It is important to acknowledge the current need to measure qubits immediately limits application to specific types of quantum computers. BB84 states, encoding data onto individual photons alongside random scrambling techniques created a new protocol durable against even powerful eavesdroppers attempting to intercept and decipher transmitted information.

This research demonstrated secure retrieval of one bit from a 104-bit database using only noisy intermediate-scale quantum (NISQ) devices without long-term memory. The method achieves information-theoretic security by measuring each qubit upon arrival and employing a block length of approximately one thousand qubits for operation. This approach provides privacy for both the user requesting the data and the database itself, protecting it from an all-powerful eavesdropper. Authors suggest future work will focus on adapting this technique alongside advancements in longer coherence times within quantum computing architectures.

👉 More information
🗞 One-Way Quantum Symmetric Private Information Retrieval Protocol From A Single Database Server Using NISQ Devices
✍️ Xiang Zou (University of Toronto); H. F. Chau (The University of Hong Kong)
🧠 ArXiv: https://arxiv.org/abs/2610.02093

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Ivy Delaney

Ivy Delaney has been working with neural networks and machine learning since the mid-nineties, back when a couple of hidden layers and a long afternoon of training counted as ambitious. She has watched the field go from academic curiosity to the thing quietly running underneath everything, and she brings that long view to quantum computing. For Quantum Zeitgeist she covers the ground where the two fields meet. That means quantum machine learning and the variational algorithms it leans on, and it also means the less glamorous but more interesting story of classical machine learning already doing real work inside quantum machines, decoding error-correcting codes, calibrating noisy hardware and learning the error models that simulators depend on. She writes about the hardware those algorithms have to run on too, and about the post-quantum cryptography scramble that the same hardware has set off. Her stories typically start with the paper, whether that is peer-reviewed work, conference proceedings or an arXiv preprint, with the source linked so you can hold a claim up against the research it came from. She is unimpressed by benchmarks that will not say what they beat, and by demonstrations that only work in the press release.

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