Flexible quantum private queries based on quantum key distribution

By adding a parameter theta in M. Jakobi et al's protocol [Phys. Rev. A 83, 022301 (2011)], we present a flexible quantum-key-distribution-based protocol for quantum private queries. We show that, by adjusting the value of theta, the average number of the key bits Alice obtains can be located on any fixed value the users wanted for any database size. And the parameter k is generally smaller (even k = 1 can be achieved) when theta < pi/4, which implies lower complexity of both quantum and classical communications. Furthermore, the users can choose a smaller theta to get better database security, or a larger theta to obtain a lower probability with which Bob can correctly guess the address of Alice's query. (C) 2012 Optical Society of America