Multidimensional Hyperentangled Photon Graph States: Creation, Validation and Application (HyperGraph)

At the heart of quantum physics and quantum technology lies the captivating phenomenon of entanglement, which society hopes to profit from in improved and completely novel technical applications within the second quantum revolution.

Entangled quantum states are extremely difficult to create and validate; only 50 years ago entangled states were shown to violate Bell’s inequalities, using two entangled quantized states of electromagnetic radiation, known as single photon states. For this achievement the 2022 Nobel Prize in Physics was awarded.

Ever since, entangled states have driven fundamental and applied research. Intriguingly, entanglement can theoretically be created between an arbitrary number of photons. Their creation, however, has been very challenging, and over the past years, the size of one-dimensional entangled photon states has been increased to 14 in 2022. The slow progress is mainly limited by the development of deterministic single photon sources.

Recently, I have designed a novel spin-photon interface in diamond with record-high emitter to detector efficiencies theoretically exceeding 99% and realistically reaching 90%. These record efficiencies are enabled by the Sawfish interface. Multiplexing of several of such interfaces will enable the creation of large 2D and even 3D photon graph states.

These states will be so complex, that new theoretical models are required for their understanding. The usage of states whose density matrix could never be computed on classical computers is indeed a conceptual problem in theory. In this regime, HyperGraph’s experimental research will stimulate concepts and new discoveries in theory. Moreover, because of the many degrees of interconnection between the individual qubits, I expect innovative concepts for error correction, novel and possibly improved protocols in fault tolerant quantum information processing, and even completely new application cases to be developed in parallel and beyond HyperGraph.