Deterministic freely propagating photonic qubits with negative Wigner functions

Engineering the quantum states of freely propagating light is of paramount importance for quantum technologies. As yet, the experimental generation of photonic states with negative Wigner functions has relied intrinsically on probabilistic schemes, heralded by the projection of a quantum measurement. Here we describe the fully deterministic preparation of freely propagating quantum states of light with negative Wigner functions, obtained by mapping the internal state of an intracavity Rydberg superatom onto an optical qubit encoded as a superposition of 0 and 1 photons. This approach enables us to reach a 60% photon generation efficiency in a well-controlled spatiotemporal mode while maintaining strong photon antibunching. By changing the qubit rotation angle, we observe an evolution from quadrature squeezing to Wigner negativity. Our experiment demonstrates this new technique as a viable method for deterministically generating non-Gaussian photonic resources, lifting several major roadblocks in optical quantum engineering. Non-Gaussian Wigner-negative freely propagating optical quantum states are deterministically generated with a 60% photon generation efficiency. An evolution from quadrature squeezing to Wigner negativity is observed by changing the qubit rotation angle.

Automated summary

Freely propagating optical quantum states with negative Wigner functions are deterministically generated with a 60% photon generation efficiency by mapping the internal state of an intracavity Rydberg superatom onto an optical qubit. The evolution from quadrature squeezing to Wigner negativity is observed by changing the qubit rotation angle. This experiment overcomes major roadblocks in optical quantum engineering.