  The generation, manipulation and fundamental understanding of entanglement
lies at very heart of quantum mechanics. Among various types of entangled
states, the NOON states are a kind of special quantum entangled states with two
orthogonal component states in maximal superposition, which have a wide range
of potential applications in quantum communication and quantum information
processing. Here, we propose a fast and simple scheme for generating NOON
states of photons in two superconducting resonators by using a single
superconducting transmon qutrit. Because only one superconducting qutrit and
two resonators are used, the experimental setup for this scheme is much
simplified when compared with the previous proposals requiring a setup of two
superconducting qutrits and three cavities. In addition, this scheme is easier
and faster to implement than the previous proposals, which require using a
complex microwave pulse, or a small pulse Rabi frequency in order to avoid
nonresonant transitions.
