Private Database Queries Using Quantum States with Limited Coherence Times

TL;DR

This paper introduces a quantum-based method for private database queries that leverages limited coherence times, enabling users to privately access data and compute functions without revealing additional information, especially effective for small data items.

Contribution

The paper presents a novel quantum protocol for private database queries that functions effectively with limited coherence times, reducing cryptographic overhead.

Findings

Allows private access to one database item using quantum states

Enables computation of functions like XOR without extra information gain

Effective for small data items with limited quantum coherence

Abstract

We describe a method for private database queries using exchange of quantum states with bits encoded in mutually incompatible bases. For technology with limited coherence time, the database vendor can announce the encoding after a suitable delay to allow the user to privately learn one of two items in the database without the ability to also definitely infer the second item. This quantum approach also allows the user to choose to learn other functions of the items, such as the exclusive-or of their bits, but not to gain more information than equivalent to learning one item, on average. This method is especially useful for items consisting of a few bits by avoiding the substantial overhead of conventional cryptographic approaches.