Non-classical states of light such as single photons and entangled photons are key ingredients for chips dedicated to quantum computation, quantum sensing, quantum measurement, etc. Fabrication of a traditional chip is hard, but with billions of dollars of specialized equipment (and guys in white bunny suits) it can be done. Fabrication of a quantum chip is even harder. In addition, sources of non-linear light are needed, and making these light sources fabricable is essential.
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Source: Phys.org