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arXiv:1705.05272 · Physical Review Letters

Correlations and Entanglement of Microwave Photons Emitted in a Cascade Decay

Simone Gasparinetti, Marek Pechal, Jean-Claude Besse, Mintu Mondal, Christopher Eichler, Andreas J. Wallraff

Published Oct 4, 2017• 44 citations
arXivHTMLPDF

Abstract

We use a three-level artificial atom in the ladder configuration as a source of correlated, single microwave photons of different frequency. The artificial atom, a transmon-type superconducting circuit, is driven at the two-photon transition between ground and second-excited state, and embedded into an on-chip switch that selectively routes different-frequency photons into different spatial modes. Under continuous driving, we measure power cross-correlations between the two modes and observe a crossover between strong antibunching and superbunching, typical of cascade decay, and an oscillatory pattern as the drive strength becomes comparable to the radiative decay rate. By preparing the source in a superposition state using an excitation pulse, we achieve deterministic generation of entangled photon pairs, as demonstrated by nonvanishing phase correlations and more generally by joint quantum state tomography of the two itinerant photonic modes.

DOI
10.1103/physrevlett.119.140504

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Abstract A dynamical control of the coupling strengths between dressed states and probe photon states is demonstrated with a transmon-like artificial atom coupled to two closely spaced resonant modes. When the atom is driven with one mode, the atom state and driving photon states are superposed, forming the dressed states. Dressed states with 1st, 2nd and 3rd excited states of the atom were prepared and probed via the strong coupling to the other resonant mode. Spectroscopy reveals that the coupling strengths are ``dressed" and can be modulated by the power and sideband index of the driving. The transmission of the probe tone is modulated by the driving microwave amplitude with a Bessel behavior, displaying multi-photon process associated with the inter-atomic level transitions.
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