Direct Estimations of Linear and Nonlinear Functionals of a Quantum State
Direct Estimations of Linear and Nonlinear Functionals of a Quantum State
We present a simple quantum network, based on the controlled-SWAP gate, that can extract certain properties of quantum states without recourse to quantum tomography. It can be used as a basic building block for direct quantum estimations of both linear and nonlinear functionals of any density operator. The network has …