Multi-user Quantum Private Query

Quantum private query is an encrypted communication protocol to protect both user privacy and database privacy.It is an extension of classic symmetric privacy information retrieval in quantum field.Compared with symmetric privacy query,the security of symmetric privacy query depends on the assumption of mathematical difficulties,while the security of quantum privacy query depends on the basic physical characteristics of quantum mechanics.Moreover,quantum privacy query has obvious advantages in communication complexity,computational complexity and reliability.The previous quantum privacy query protocols usually considered single user retrieval and need to repeatedly execute multiple times between each user and the database when multiple users want to retrieve information from the database.Thereby,it is worth researching that multiple users simultaneously retrieve information from the database.In addition,as the quantum devices are extreme expensive and only a few companies can afford it,it is worth concerning that decrease the quantum ability of the user and the database.Besides,since the noise environment has a negative impact on the process of quantum communication,it is vital that resisting the noisy environment.Therefore,the main contents of this thesis are as follows:1.A multi-user quantum privacy query protocol is proposed.This protocol focuses on a specific scenario of multi-user retrieval,where multiple users cooperate to complete a task and need to retrieve the same information from the database safely.On the premise of protecting the privacy of the users and the database,users can simultaneously retrieve database information by the entanglement swapping technology of multi-particle GHZ state.2.A multi-user quantum privacy query protocol with classic participants is proposed,where most quantum operations performed by users and databases are delegated to a quantum center.It makes the users and the database almost classical and only need to have the abilities of accessing quantum channels and rearranging quantum bits.3.A multi-user quantum privacy query protocol with classic participants over collective noise channels is proposed,in which the decoherence free state in the decoherence free subspace is used to construct the quantum resource state by the property that the logic multi particle GHZ state remains unchanged under the influence of joint noise.In conclusion,this thesis proposes a multi-user quantum privacy query protocol,which extends the quantum privacy query protocol of a single user to any number of users.On this basis,a multi-user quantum privacy query protocol with classic participants is proposed,which reduces the quantum capabilities requirement of the users and the database.Besides,a multi-user quantum privacy query protocol with classic participants over collective noise channels is proposed,which can resist joint noise environment.