A Schrodinger Cat Living in Two Boxes
  Quantum superpositions of distinct coherent states in a single-mode harmonic oscillator, known as "cat states", have been an elegant demonstration of Schrodinger'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, Yvonne Y. Gao, Philip Reinhold, R. W. Heeres, Nissim Ofek,   Kevin Chou, Christopher Axline, Matthew Reagor, Jaco...
quant-ph