Implementation of unambiguous comparison for unknown pure quantum states with cavity-assisted interaction

We propose two effective schemes for local and remote unknown atomic state comparisons with a cavity-assisted single photon input--output process without any initial entanglement or auxiliary resource. The unambiguous state discrim- ination is considered using the state comparison process as the basic module. All the implementation schemes here just involve common quantum logic gates and the single qubit measurement. The analysis shows that our schemes are feasible under the current experimental conditions.