Quantum Private Query With Perfect Performance Universally Applicable Against Collective-Noise

Almost all of the previous quantum private query (QPQ) protocols are always based on an ideal environment without any noise. Nevertheless, due to the defects of the channel, channel noise inevitably exists in the actual transmission process, which will give rise to transmission error and reduce the probability of successful quantum transmission. An eavesdropper may disguise her actions as channel noise to avoid being detected by legitimate parties during security checks. To solve this problem, we present a QPQ protocol with perfect performance universally applicable against collective noise. Concretely, the protocol encodes bits in noiseless subspace and thus can function over a quantum channel subjected to an arbitrary degree of collective noise, as occurs, for instance, due to polarization rotation in an optical fiber. Furthermore, Bob cannot get the information about Alice's choice at all by taking fake entangled attack and by taking fake photon attack, the probability Bob can get the information about Alice's choice is only approximately 6.7%, which is far less than the probability of 25% in Yang et al.'s protocol. Moreover, the conclusiveness of the user Alice's measurement results is subject to quantum randomness rather than allowing Alice to choose by herself to obtain a conclusive result in Wei et al.'s protocol, which prevents Alice's intuitive attack and meanwhile makes it arduous for Bob to perform the joint-measurement attack. Our protocol uses only one state, which reduces the communication complexity, and is, therefore, an effective QPQ solution with the high-security level.