Weaving independently generated photons into an arbitrary graph state

The controlled Z (CZ) operations acting separately on pairs of qubits are commonly adopted in the schemes of generating graph states, the multi-partite entangled states for the one-way quantum computing. For this purpose, we propose a setup of cascade CZ operation on a whole group of qubits in sequence. The operation of the setup starts with entangling an ancilla photon to the first photon as qubit, and this ancilla automatically moves from one entanglement link to another in assisting the formation of a string in graph states. The generation of some special types of graph states, such as the three-dimensional ones, can be greatly simplified in this approach. The setup presented uses weak nonlinearities, but an implementation using probabilistic linear optics is also possible.Comment: 6 pages, 7 figures. Accepted by Phys. Rev.

Searching for a stop-pair sample from top counting experiments at hadron colliders

The light stop pair if produced in hadron colliders and decaying through the likely decay chain stop->chargino + b followed by chargino->neutralino + f f', can mimic closely a top quark event when the mass of the stop is close to that of the top quark. Because of the much lower production rate, the stop event can be buried under the top quark event sample. In order to uncover the stop event, specific selection cuts need to be applied. Through Monte Carlo simulation with suitable kinematic cuts, we found that such stop event can be extracted from the top quark sample and detected by the top quark counting experiments in the upcoming upgraded Tevatron and LHC. However, because of the small statistics of the Run 1 of the Tevatron, the stop signal remains hidden at Run 1.Comment: 17 pages, 4 figure