Generating nonclassical states for continuous-variable quantum computation Using Photon-Number Selective Phase Gates and Displacements

Efficiently controlling the quantum state of 3D cavity modes is an important ingredient for exploiting their long lifetimes and restricted decoherence channels for quantum information processing. Here we experimentally explore the use of Photon-Number Selective Phase (SNAP) gates and displacements to generate Wigner-negative states useful for continuous variable quantum computing. Our state-preparation protocol consists of a sequence of interleaved SNAP gates and coherent displacements. We use gradient descent algorithm to optimize the parameters of the sequence, and characterize fidelities to the target state by Wigner tomography. It has been shown theoretically that just a few of these blocks can be used to generate highly nonclassical states with high fidelity.