paper

Emission of photon multiplets by a dc-biased superconducting circuit

arXiv:2111.09604 · doi:10.1103/PhysRevX.12.021006

Abstract

We observe the emission of bunches of photons by a circuit made of a microwave resonator in series with a voltage-biased tunable Josephson junction. The bunches are emitted at specific values of the bias voltage, for which each Cooper pair tunneling across the junction creates exactly k photons in the resonator. The latter is a micro-fabricated spiral coil which resonates and leaks photons at 4.4~GHz in a measurement line. Its characteristic impedance of 1.97~k is high enough to reach a strong junction-resonator coupling and a bright emission of the k-photon bunches. We show that a RWA treatment of the system accounts quantitatively for the observed radiation intensity, from to , and over three orders of magnitude when varying the Josephson energy . We also measure the second order correlation function of the radiated microwave to determine its Fano factor , which in the low limit, confirms with the emission of photon bunches. At larger , a more complex behavior is observed in quantitative agreement with numerical simulations.

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