Friday, July 5, 2019 1:00 pm
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1:00 pm
EDT (GMT -04:00)
Two-photon and Three-photon Parametric Interactions in Superconducting Microwave Circuits
Sandbo Chang
Parametric processes in a microwave system are a source of nonclassical radiation with a number of potential applications in quantum information processing. We have implemented and experimentally verified a source of entangled microwave fields. Implementing a tunable, multimode microwave resonator with 3 modes in the common 4-8 GHz range, we performed two-mode parametric down-conversion between pairs of modes and observed the induced correlations in their voltage quadratures. With the system gain and noise calibrated using a shot noise tunnel junction, we have verified pairwise entanglement among the frequency modes. By introducing a second pump tone, we have demonstrated that it is also possible to generate genuine tripartite entanglement between all three modes.
Further, advancing to higher-order parametric processes has been an on-going challenge. In particular, a long-sought goal in quantum optics has been third-order spontaneous parametric down-conversion (SPDC), where photons are directly created in triplets. We report the generation of microwave signals from third-order SPDC in a multimode parametric cavity when pumping both a single mode and three coupled modes. By pumping at the triple frequency of a single mode, we observe a phase-space distribution with a non-Gaussian profile which shows strong skewness in the quadrature amplitude distribution. By pumping at the sum frequency of three modes, we observe non-zero coskewness between the quadrature amplitudes of the modes. These phase-dependent three-mode correlations are observed even though the two-mode covariance between any two of the modes is zero. This suggest the existence of a nontrivial three-mode continuous variable interference. These types of non-Gaussian states have been suggested as a resource enabling universal quantum computation with continuous variables. The multimode states may also be useful for three-party quantum communication protocols such as quantum secret sharing.