Experimental symmetric private information retrieval with measurement-device-independent quantum network

Retrieving information from a database, or information retrieval (IR), is a simple task with an expansive range of applications. However, oftentimes, the user and data centres involved in IR tasks would have privacy concerns. To this end, we require symmetric private information retrieval (SPIR), which possesses stringent system requirements that are challenging to meet in practice. This is especially so for SPIR with databases needing long-term security, for which the use of multiple data centres and a secure method of key distribution are necessary. In this paper, we report an experimental implementation of SPIR with information-theoretic secure keys generated by measurement-device-independent (MDI) QKD. In particular, we demonstrate the SPIR scheme on a simple fingerprint database, successfully retrieving a 582-byte fingerprint file from a database with 800 entries. Our simulation and experimental results show the feasibility of the proposed SPIR scheme, presenting a promising way for practical IR applications with privacy requirements.