Quantum superpositions of distinct coherent states in a single-mode harmonic oscillator, known as “cat states”, have been an elegant demonstration of Schrödinger’s famous cat paradox. Here, we realize a two-mode cat state of electromagnetic fields in two microwave cavities bridged by a superconducting artificial atom, which can also be viewed as an entangled pair of single-cavity cat states. We present full quantum state tomography of this complex cat state over a Hilbert space exceeding 100 dimensions via quantum non-demolition measurements of the joint photon number parity. The ability to manipulate such multi-cavity quantum states paves the way for logical operations between redundantly encoded qubits for fault-tolerant quantum computation and communication.
Chen Wang is a postdoctoral associate at the Yale University, where he works in the group of Prof. Robert Schoelkopf on quantum information science using superconducting circuits. He is moving to University of Massachusetts-Amherst as an assistant professor in Department of Physics. Chen received his B.S. degree from Peking University in 2006, and his Ph.D. from Cornell University in 2012.