Resource-Efficient Direct Entanglement Measurement of Werner State with Hybrid Spin-Photon Interaction System

We propose two resource-efficient schemes of direct entanglement measurement of two-qubit Werner states via hybrid interaction system with nitrogen-vacancy (NV) center coupled to micro-cavity. Based on the unconventional encoding mode on auxiliary qubits, our physical unit can realize the hybrid controlled phase gate and controlled-NOT gate between spin and polarization qubits. Utilizing only one copy of initial entangled state, we implement direct concurrence measurement of spin Werner states in NV centers and polarization Werner states of single photons. Both schemes can be transformed into remote ones with the initial entangled states possessed by spatially separated participants. Experimental feasibility analyses indicate that the presented schemes have reliable performance in the current available experimental conditions.