A near deterministic linear optical CNOT gate

quantum information, deterministic linear optical gates, conditional measurements, hybrid systems We show how to construct a near deterministic CNOT using several single photons sources, linear optics, photon number resolving quantum non-demolition detectors and feed-forward. This gate does not require the use of massively entangled states common to other implementations and is very efficient on resources. Only two ancilla photons are required for the operation of the gate and these are not destroyed in the conditioning process. The key element of this gate are non-demolition detectors that use a weak cross Kerr nonlinearity effect to conditionally generate a phase shift on a coherent probe, if a photon is present in the signal mode. These potential phase shifts can then be measured using highly efficient homodyne detection.