S. Dambach

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

Antibunched photons emitted by a dc biased Josephson junction

  1. C. Rolland,
  2. A. Peugeot,
  3. S. Dambach,
  4. M. Westig,
  5. B. Kubala,
  6. C. Altimiras,
  7. H. le Sueur,
  8. P. Joyez,
  9. D. Vion,
  10. P. Roche,
  11. D. Esteve,
  12. J. Ankerhold,
  13. and F. Portier
We show experimentally that a dc biased Josephson junction in series with a high-enough impedance microwave resonator emits antibunched photons. Our resonator is made of a simple micro-fabricated
spiral coil that resonates at 4.4 GHz and reaches a 1.97 kΩ characteristic impedance. The second order correlation function of the power leaking out of the resonator drops down to 0.3 at zero delay, which demonstrates the antibunching of the photons emitted by the circuit at a rate of 6 10^7 photons per second. Results are found in quantitative agreement with our theoretical predictions. This simple scheme could offer an efficient and bright single-photon source in the microwave domain.
arxiv pdf