  Schr\"odinger cat states, quantum superpositions of macroscopically distinct
classical states, are an important resource for quantum communication, quantum
metrology and quantum computation. Especially, cat states in a phase space
protected against phase-flip errors can be used as a logical qubit. However,
cat states, normally generated in three-dimensional cavities, are facing the
challenges of scalability and controllability. Here, we present a novel
strategy to generate and store cat states in a coplanar superconducting circuit
by the fast modulation of Kerr nonlinearity. At the Kerr-free work point, our
cat states are passively preserved due to the vanishing Kerr effect. We are
able to prepare a 2-component cat state in our chip-based device with a
fidelity reaching 89.1% under a 96 ns gate time. Our scheme shows an excellent
route to constructing a chip-based bosonic quantum processor.
