Kerr Combs and Telecommunications Components for the Generation and High-Dimensional Quantum Processing of d-Level Cluster States

Large and complex optical quantum states are a key resource for fundamental science and applications such as quantum communications, information processing, and metrology. In this context, cluster states are a particularly important class because they enable the realization of universal quantum computers by means of the so-called 'one-way' scheme, where processing operations are performed through measurements on the state. While two-level (i.e. qubit) cluster states have been realized thus far, further boosting this computational resource by increasing the number of particles comes at the price of significantly reduced coherence time and detection rates, as well as increased sensitivity to noise. In contrast, the realization of d-level (with d > 2) cluster states offers the possibility to increase quantum resources without changing the number of particles, enables the implementation of efficient computational protocols, as well as coincides with a reduction in the noise sensitivity of the states. Here, we experimentally realize, characterize, and perform one-way processing operations on three-level, four-partite cluster states formed by two photons in the time and frequency domain. We make use of a unique approach based on integrated photonic chips and optical fiber communications components, enabling scalable, deterministic new functionalities.