Quantum databases open an exciting new frontier in data management by offering privacy guarantees that classical systems cannot match. Traditional engines tackle user privacy, which hides the records being queried, or data privacy, which prevents a user from learning more than she has queried. We propose a quantum database that protects both by leveraging quantum mechanics: when the user measures her chosen basis, the superposition collapses and the unqueried rows become physically inaccessible. We encode relational tables as a sequence of Quantum Random Access Codes (QRACs) over mutually unbiased bases (MUBs), transmit a bounded number of quantum states, and let a single, destructive measurement reconstruct only the selected tuple. This allows us to preserve data privacy and user privacy at once without trusted hardware or heavyweight cryptography. Moreover, we envision a novel hybrid quantum-classical architecture ready for early deployment, which ensures compatibility with the limitations of today's Noisy Intermediate-Scale Quantum devices.

翻译：量子数据库通过提供经典系统无法比拟的隐私保障，为数据管理开辟了一个令人兴奋的新前沿。传统引擎要么处理用户隐私（即隐藏被查询的记录），要么处理数据隐私（即防止用户获取超出其查询范围的信息）。我们提出了一种利用量子力学同时保护两者的量子数据库：当用户测量其选定的基时，叠加态坍缩，未查询的行在物理上变得不可访问。我们将关系表编码为一系列基于相互无偏基的量子随机访问码，传输有限数量的量子态，并通过一次破坏性测量仅重构选定的元组。这使得我们无需可信硬件或重量级密码学即可同时保护数据隐私和用户隐私。此外，我们设想了一种适合早期部署的新型混合量子-经典架构，确保与当前含噪声中等规模量子设备的限制兼容。