Experimental preparation of generalized and multipartite cat states for flying microwave photons

Preparing Schrödinger's cat states has attracted wide research interest from testing quantum foundations to demonstrating the increasing controllability of modern quantum systems. In recent years, Schrödinger's cat states have been successfully prepared in various physical systems, including vibrational states of a trapped ion, propagating photon modes and microwave photons confined in superconducting cavities coupled with either Rydberg atoms or superconducting qubits. Here, we demonstrate a versatile and highly-scalable scheme to deterministically create generalized and multipartite flying cat states in the microwave domain, by reflecting coherent states photons from a microwave cavity containing a superconducting qubit. The full control over the superposition and entanglement of the prepared states is realized by the coherent control of the qubit state. We have performed full quantum state tomography on the generated states to reveal the distinct non-classical feature in the statistical properties of photon field, and verify quantum entanglement with up to four photonic modes. Our work presents a powerful toolbox for researching quantum metrology and many quantum information processing protocols based on cat states.