  Linear bosonic modes offer a hardware-efficient alternative for quantum
information processing but require access to some nonlinearity for universal
control. The lack of nonlinearity in photonics has led to encoded
measurement-based quantum computing, which rely on linear operations but
requires access to resourceful ('nonlinear') quantum states, such as cubic
phase states. In contrast, superconducting microwave circuits offer
engineerable nonlinearities but suffer from static Kerr nonlinearity. Here, we
demonstrate universal control of a bosonic mode composed of a superconducting
nonlinear asymmetric inductive element (SNAIL) resonator, enabled by native
nonlinearities in the SNAIL element. We suppress static nonlinearities by
operating the SNAIL in the vicinity of its Kerr-free point and dynamically
activate nonlinearities up to third order by fast flux pulses. We
experimentally realize a universal set of generalized squeezing operations, as
well as the cubic phase gate, and exploit them to deterministically prepare a
cubic phase state in 60 ns. Our results initiate the experimental field of
universal continuous-variables quantum computing.
