Frequency hopping in quantum interferometry



We have realized the nonlinear frequency conversion of optical quantum superposition states in a new kind of Mach-Zehnder interferometer which is terminated at two different frequencies. The information-preserving character of the relevant unitary transformation represented by the nonlinear process has been experimentally demonstrated in the cases of input qubits and ebits. The theoretical expression of the quantum efficiency of the process is compared with the experimental results. Besides its own intrinsic fundamental interest, the new scheme is expected to find important applications in modern quantum information technology.