Christopher Wilson, Chalmers University of Technology Sweden
Abstract
It recent years, it has been realized that the strong, dissipationless nonlinearity provided by superconducting Josephson junctions can be used to generate nonclassical states of light in the microwave regime. This has led to the rapid development of the fledgling field of microwave quantum optics. Here we describe a series of experiments in this field. In the first set of experiments, we investigate the possibility of generating photons from the vacuum using nonadiabatic perturbations of the electromagnetic field. In particular, we investigate the dynamical Casimir effect, an effect first predicted over 40 years ago. We change the electrical length of an open transmission line using the tunable inductance of a SQUID that terminates the line. By modulating the SQUID at ~10 GHz, we change the electrical length of the line at a substantial fraction of the speed of light. We observe broadband photon generation in quantitative agreement with theory. We are also able to observe broadband two-mode squeezing of the emitted radiation. In the second experiment, we have embedded an artificial atom, a superconducting "transmon" qubit, in a 1D open space and investigated the scattering of incident microwave photons. When an input coherent state, with an average photon number much less than 1, is on resonance with the artificial atom, we observe extinction of up to 99% in the forward propagating field. We also study the statistics of the reflected and transmitted beams, which are predicted to be nonclassical states. In particular, we demonstrate photon antibunching in the reflected beam by measuring the g2 function.