P. Milman

Generating two continuous entangled microwave beams using a dc-biased Josephson junction

  1. A. Peugeot,
  2. G. Ménard,
  3. S. Dambach,
  4. M. Westig,
  5. B. Kubala,
  6. Y. Mukharsky,
  7. C. Altimiras,
  8. P. Joyez,
  9. D. Vion,
  10. P. Roche,
  11. D. Esteve,
  12. P. Milman,
  13. J. Leppäkangas,
  14. G. Johansson,
  15. M. Hofheinz,
  16. J. Ankerhold,
  17. and F. Portier
We show experimentally that a dc-biased Josephson junction in series with two microwave resonators emits entangled beams of microwaves leaking out of the resonators. In the absence
of a stationary phase reference for characterizing the entanglement of the outgoing beams, we measure second-order coherence functions for proving entanglement up to an emission rate of 2.5 billion photon pairs per second. The experimental results are found in quantitative agreement with theory, proving that the low frequency noise of the dc bias is the main limitation for the coherence time of the entangled beams. This agreement allows us to evaluate the entropy of entanglement of the resonators, and to identify the improvements that could bring this device closer to a useful bright source of entangled microwaves for quantum-technological applications.
arxiv pdf

Quantum simulation of ultrastrongly coupled bosonic modes using superconducting circuits

  1. S. Fedortchenko,
  2. S. Felicetti,
  3. D. Marković,
  4. S. Jezouin,
  5. A. Keller,
  6. T. Coudreau,
  7. B. Huard,
  8. and P. Milman
The ground state of a pair of ultrastrongly coupled bosonic modes is predicted to be a two-mode squeezed vacuum. However, the corresponding quantum correlations are currently unobservable
in condensed matter where such a coupling can be reached, since it cannot be extracted from these systems. Here, we show that superconducting circuits can be used to perform an analog simulation of a system of two bosonic modes in regimes ranging from strong to ultrastrong coupling. More importantly, our quantum simulation set-up enables to detect output excitations that are related to the ground state properties of the bosonic modes. We compute the emission spectra of this physical system and show that the produced state presents single and two-mode squeezing simultaneously.
arxiv pdf