  Entanglement between large numbers of quantum modes is the quintessential
resource for future technologies such as the quantum internet. Conventionally
the generation of multimode entanglement in optics requires complex layouts of
beam-splitters and phase shifters in order to transform the input modes in to
entangled modes. These networks need substantial modification for every new set
of entangled modes to be generated. Here we report on the highly versatile and
efficient generation of various multimode entangled states with the ability to
switch between different linear optics networks in real time. By defining our
modes to be combinations of different spatial regions of one beam, we may use
just one pair of multi-pixel detectors each with M photodiodes in order to
measure N entangled modes, with a maximum number of N=M modes. We program
virtual networks that are fully equivalent to the physical linear optics
networks they are emulating. We present results for N=2 up to N=8 entangled
modes here, including N=2,3,4 cluster states. Our approach introduces
flexibility and scalability to multimode entanglement, two important attributes
that are highly sought after in state of the art devices.

Quantum Physics