Radiative Properties of an Artificial Atom coupled to a Josephson Junction Array

  1. Kanu Sinha,
  2. Saeed A. Khan,
  3. Elif Cüce,
  4. and Hakan E. Türeci
We study the radiative properties — the Lamb shift, Purcell decay rate and the spontaneous emission dynamics — of an artificial atom coupled to a long, multimode cavity
formed by an array of Josephson junctions. Introducing a tunable coupling element between the atom and the array, we demonstrate that such a system can exhibit a crossover from a perturbative to non-perturbative regime of light-matter interaction as one strengthens the coupling between the atom and the Josephson junction array (JJA). As a consequence, the concept of spontaneous emission as the occupation of the local atomic site being governed by a single complex-valued exponent breaks down. This breakdown, we show, can be interpreted in terms of formation of hybrid atom-resonator modes with radiative losses that are non-trivially related to the effective coupling between individual modes. We develop a singular function expansion approach for the description of the open quantum system dynamics in such a multimode non-perturbative regime. This modal framework generalizes the normal mode description of quantum fields in a finite volume, incorporating exact radiative losses and incident quantum noise at the delimiting surface. Our results are pertinent to recent experiments with Josephson atoms coupled to high impedance Josephson junction arrays.

Studying Light-Harvesting Models with Superconducting Circuits

  1. Anton Potočnik,
  2. Arno Bargerbos,
  3. Florian A. Y. N. Schröder,
  4. Saeed A. Khan,
  5. Michele C. Collodo,
  6. Simone Gasparinetti,
  7. Yves Salathé,
  8. Celestino Creatore,
  9. Christopher Eichler,
  10. Hakan E. Türeci,
  11. Alex W. Chin,
  12. and Andreas Wallraff
The process of photosynthesis, the main source of energy in the animate world, converts sunlight into chemical energy. The surprisingly high efficiency of this process is believed to
be enabled by an intricate interplay between the quantum nature of molecular structures in photosynthetic complexes and their interaction with the environment. Investigating these effects in biological samples is challenging due to their complex and disordered structure. Here we experimentally demonstrate a new approach for studying photosynthetic models based on superconducting quantum circuits. In particular, we demonstrate the unprecedented versatility and control of our method in an engineered three-site model of a pigment protein complex with realistic parameters scaled down in energy by a factor of 105. With this system we show that the excitation transport between quantum coherent sites disordered in energy can be enabled through the interaction with environmental noise. We also show that the efficiency of the process is maximized for structured noise resembling intramolecular phononic environments found in photosynthetic complexes.