Quantum transduction via frequency upconversion (invited)

We describe a method for efficiently and coherently converting photons from one wavelength to another through the process of nonlinear upconversion. By using an intense 1064 nm escort laser pulse and a periodically poled lithium niobate (PPLN) crystal, we demonstrate upconversion efficiency of 99% and coherence of 95% for 1550 to 631 nm light at the single-photon level, thereby qualifying it for use in manipulation of photonic qubits. We then show how to create photons in arbitrary superpositions of different energy states, thereby enlarging the accessible Hilbert space for quantum information applications.