A flying Schrödinger cat in multipartite entangled states

  1. Zhiling Wang,
  2. Zenghui Bao,
  3. Yukai Wu,
  4. Yan Li,
  5. Weizhou Cai,
  6. Weiting Wang,
  7. Yuwei Ma,
  8. Tianqi Cai,
  9. Xiyue Han,
  10. Jiahui Wang,
  11. Yipu Song,
  12. Luyan Sun,
  13. Hongyi Zhang,
  14. and Luming Duan
Schrödinger’s cat originates from the famous thought experiment querying the counterintuitive quantum superposition of macroscopic objects. As a natural extension, several „cats“ (quasi-classical objects) can be prepared into coherent quantum superposition states, which is known as multipartite cat states demonstrating quantum entanglement among macroscopically distinct objects. Here we present a highly scalable approach to deterministically create flying multipartite Schrödinger cat states, by reflecting coherent state photons from a microwave cavity containing a superconducting qubit. We perform full quantum state tomography on the cat states with up to four photonic modes and confirm the existence of quantum entanglement among them. We also witness the hybrid entanglement between discrete-variable states (the qubit) and continuous-variable states (the flying multipartite cat) through a joint quantum state tomography. Our work demonstrates an important experimental control method in the microwave region and provides an enabling step for implementing a series of quantum metrology and quantum information processing protocols based on cat states.
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