The Cavity-embedded-cooper Pair Transistor

Nearly eight decades after Erwin Schrödinger proposed his famous cat paradox, the boundary between classical and quantum physics is becoming accessible to experimental study in condensed matter systems, in which macroscopic and microscopic degrees of freedom interact with each other. The cavity-embedded-Cooper pair transistor (cCPT) is an ideal candidate for such a study in that it is not only strongly and intrinsically nonlinear but also fully quantum mechanical. A novel technique, based on the circuit quantum electrodynamics architecture, is first introduced for applying a dc bias to a high-Q superconducting microwave cavity. The development and investigation of the cCPT system, in which a Cooper pair transistor acting as a single artificial atom is directly coupled to an on-chip dc-biased high-Q resonator, is then presented. Self-oscillations in the cCPT, internally driven by the ac Josephson effect, demonstrate the strong and phase coherent coupling between matter and light in the cCPT. Meanwhile, photons continually produced by the system are collected and characterized by quantum state tomography, which indicates the nonclassical nature of the emitted light and the nonlinear quantum dynamics of the cCPT system.