We observed a remarkably broad sum frequency generation quasi-phasematching bandwidth in periodically poled KTiOPO4, consistent with theory. This is key to large-size quantum computing registers by generating continuous-variable cluster states in quantum optical frequency combs.
We report on our research effort to generate large-scale multipartite optical-mode entanglement using as few physical resources as possible. We have previously shown that cluster-and GHZ-type N-partite continuous-variable entanglement can be obtained in an optical resonator that contains a suitably designed second-order nonlinear optical medium, pumped by at most O (N 2) fields. In this paper, we show that the frequency comb of such a resonator can be entangled in an arbitrary number of independent 2 × 2 and 2 × 3 continuousvariable cluster states by a single optical parametric oscillator pumped by just a few optical modes.