  We theoretically investigate the dynamical Casimir effect in electrical
circuits based on superconducting microfabricated waveguides with tunable
boundary conditions. We propose to implement a rapid modulation of the boundary
conditions by tuning the applied magnetic flux through superconducting quantum
interference devices (SQUIDs) that are embedded in the waveguide circuits. We
consider two circuits: (i) An open waveguide circuit that corresponds to a
single mirror in free space, and (ii) a resonator coupled to a microfabricated
waveguide, which corresponds to a single-sided cavity in free space. We analyze
the properties of the dynamical Casimir effect in these two setups by
calculating the generated photon-flux density, output-field correlation
functions, and the quadrature squeezing spectra. We show that these properties
of the output field exhibit signatures unique to the radiation due to the
dynamical Casimir effect, and could therefore be used for distinguishing the
dynamical Casimir effect from other types of radiation in these circuits. We
also discuss the similarities and differences between the dynamical Casimir
effect, in the resonator setup, and downconversion of pump photons in
parametric oscillators.
