Full two-photon downconversion of just a single photon

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We demonstrate, both numerically and analytically, that it is possible to generate two photons from one and only one photon.

• We characterize the output two photon field and make our calculations close to reality by including losses.
• Our proposal relies on real or artificial three-level atoms with a cyclic transition strongly coupled to a one-dimensional waveguide.
• We show that close to perfect downconversion with efficiency over 99% is reachable using state-of-the-art Waveguide QED architectures such as photonic crystals or superconducting circuits.