Knitting entanglement: assembling photonic states with delay lines

The generation of entanglement between more than two particles is a major challenge for all physical realizations. It is required for the realization of many quantum information protocols, including quantum computing. Single photons are one of the most promising realizations of quantum bits (qubits), as they are easily manipulated and preserve their coherence for long times. Quantum information can be stored in many different degrees of freedom of the photons. Only recently, eight photons were entangled in a single state through their polarization degree of freedom. The main difficulties in increasing this number are the elaborated setups required and the low rates of state production.

I will present two novel and simple schemes that can in principle generate entanglement between any number of photons from a single fixed setup. Because of some special symmetries of these setups and the fact that they combine photons in different paths as well as at different times, there are some surprising consequences that challenge our understanding of non-locality and the measurement of quantum states. A roadmap for future photon entanglement sources that are suitable for quantum computation will also be presented.

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