Quantum computing technologies, such as superconducting circuit-QED systems, have allowed the exploration of novel physical phenomena. These include strongly nonlinear light-matter interactions. In this context, we analyze the properties and dynamics of generalized squeezed vacuum states, i.e. states obtained by applying a high-order squeezing operator to the vacuum state. Our numerical simulations suggest that, in stark contrast to displacement and two-photon squeezing, higher-order squeezing leads to oscillatory dynamics. The state is squeezed in the initial stages of the dynamics but the squeezing reverses at later stages, and the state reverts almost completely back to the initial state. Further investigation reveals that the simulation results depend strongly on whether the state space in the simulation contains an even or odd number of states. This result indicates that the infinite-size limit is not well defined, and it raises questions regarding whether the simulation results are physically meaningful. We show that the squeezing Hamiltonian must be complemented with additional regulating terms to make the results truncation-size independent and physically meaningful.

Sahel Ashhab, Senior Researcher, National Institute of Communication Technology, Japan

Host: Ian Low